Previous Page Table of Contents Next Page


Sergio S. Felix

In Southeast Asia there are so many lakes, rivers and reservoirs and vast coastal and estuarine areas suitable for developing the fishpen/cage industry. In the Philippines, there are 70 lakes with an aggregate area of 200 000 hectares and 30 000 hectares of reservoirs, rivers and swamps. The Philippines has 7 100 islands, big and small, such that we are endowed with vast areas of sheltered coves, lagoons, coastal areas and estuaries which could be utilized for the fishpen and cage industry. However, the success and failure in aquaculture development depend primarily on the selection of sites. It should be noted, however, that no matter how rich a body of water in natural food is as Laguna Lake for instance, not all areas are suitable for the fishpen/cage industry. There are so many factors to be considered in the selection of sites. Among the factors are:

1. Area sheltered from high wind or typhoon

It is advantageous that the site is sheltered from high wind. In Laguna Lake for example, these are the areas with buffer zone like Talim Island and the mountain ranges from Binangonan to Cardona. In coastal areas, coves and lagoons, these are the areas sheltered from high wind and strong water current (Figs. 1–4). If the site is sheltered from high wind and strong water current, damage to nets and poles and even loss of stock can be minimized.

2. Depth of the water

Generally, the depth of the water in the fishpen is not less than two meters but should not exceed seven meters. However, for fish cages the deeper the water the better. The stocking rate in fish cages is very intensive, hence, water circulation should be free to provide more oxygen content. In deep waters the organic deposits plus the faeces of the fish stock may not affect the water quality and the ecological condition of the lake water or coastal water. With high temperature and high dissolved oxygen, feeding of fish is enhanced, hence fast rate of growth is expected. In inland seas or coastal areas no less than five meters at low tide is suitable.

1 Bureau of Fisheries and Aquatic Resources, Manila, Philippines

3. Prevailing wind direction and fish food distribution

One of the principal causes of horizontal distribution of plankton, the natural food of milkfish, Chinese carps or Crucian carp, is the wind acting upon the surface waters. This is true in big lakes like Laguna Lake. As stated, wind action produces an actual drift of surface waters. In such condition of drifting waters, plankton becomes concentrated in the vicinity of the shore facing the direction of the wind. Plankton drifts are common in Laguna Lake during the dry season, that is between the months of November and June. Such plankton drifts when accumulated in small coves become so thick and change the color of the water. Plenty of algal scums are suspended in the water and algal coats cover the rocks and other solid objects. The average suspended organic matter composed of plankton and the detritus produced by the plankton in the waters of Laguna Lake is 9.5 mg/1 (on an ash-free dry basis). This is equivalent to approximately 2 400 kg/ha (by wet weight) of standing crop of primary production in the lake waters. It appears then that the plankton accumulations in the region of the exposed shores would yield much more than the average. Therefore, in selecting fishpen or fish cage sites in the lake, plankton drift caused by wind action should be given careful consideration.

Data on the prevailing wind direction, the average velocity of the wind, and the estimated velocity of surface water movement in different areas of Laguna Lake throughout the year are given in Table 1. In any body of water, tracing the meteorological and biological history is very important for site selection.

4. Lake water circulation

It is widely known that the presence of enough dissolved oxygen to keep the fish actively feeding is one of the limiting factors in fish production. An indicator of the swiftness of water current in the lake is the growth of vegetation. Normally, aquatic weeds are unable to grow heavily in environments where water currents are strong.

In areas where the fishpen belt is already established (Fig. 5) the site should be adjacent to the open water, or to the traditional passage-ways or sea lanes (buffer areas) to ensure water circulation, and enough dissolved oxygen and natural food of fishes for higher stocking rate and fast growth.

5. Availability of fish fingerlings at reasonable price

Before going into the fishpen venture, the availability of fish fingerlings as to kind and number at all times should be assured. Otherwise, the venture may be a losing one.

6. Accessibility to land and water transportation and to market

The selected site should be accessible to the market, the source of pen materials and source of fish fingerlings.

7. Water condition

Water with stable pH or slight variation is best. Turbid and polluted waters are avoided.

8. Lake bottom soil

For fishpens, soft mud, clay and clay-loam soils are the best types of bottom soil. Areas with much silt and decomposing organic matter must be avoided. For cages in inland seas or coastal areas with a depth of five meters and greater, muddy, sandy, rocky or gravally bottoms are good sites.

9. Peace and order condition

Poaching and vandalism may be rampant in certain areas. The social problems have to be considered because there are villages whose residents are peace-loving and cooperative and there are people who are really troublesome.

10. Labor

Cheap labour in the locality must also be considered.

Table 1. Wind data for the Laguna Lake area1
MonthPrevailing directionAverage velocity
Velocity of horizontal current
Number of typhoons that passed within the Lake area

1 Based on observations ranging from 8 to 47 years.

Figure 1

Figure I - The prevailing direction and velocity of horizontal currents during the period between October and January in Laguna de Bay

(Arabic numbers indicate the velocity in feet per minute)

Figure 2

Figure 2 - The prevailing direction and velocity of horizontal current during the month of February in Laguna de Bay

(Arabic numbers indicate the velocity in feet per minute)

Fig. 3

Fig. 3 - The prevailing direction and velocity of horizontal currents during the period between March to May in Laguna de Bay

(Arabic numbers indicate the velocity in feet per minute)

Figure 4

Figure 4 - The prevailing direction and velocity of horizontal currents during the period between June and September in Laguna de Bay

(Arabic numbers indicate the velocity in feet per minute)

Alejandro E. Santiago


The success of the fishpen industry in Laguna de Bay has attracted people in other countries to assess the potential of their lakes for fishpen development. This assessment involves an investigation of the most important water quality parameters or characteristics that affect fish growth and survival. Equally important is an understanding of the lake behaviour throughout the year.


2.1 Physico-chemical parameters

There are at least six (6) physico-chemical characteristics that affect fish. These are temperature, dissolved oxygen, pH, ammonia, turbidity and some toxic substances such as oil, arsenic, copper, cyanide and pesticides.

2.1.1 Temperature

The temperature of the water influences profoundly the lives of all aquatic organisms. Many fishes reproduce, feed or migrate only within certain temperature limits which may be narrow or broad according to the species.

Temperature also changes the solubility of gases like dissolved oxygen (DO). Temperature affects not only the amount of available DO but also the rate of oxygen utilization by animals so that their effect on fishes must be considered together.

The “comfortable” temperature range established for fishes is generally between 25–34°C.

Temperature is easily measured with an ordinary thermometer although a more sophisticated one like the Whitney TC-5H thermistor or YS1 54 thermistor can measure temperature in situ and at different depths.

1 SEAFDEC Aquaculture Department, Binangonan Research Station, Binangonan, Rizal, Philippines

Another important use of temperature readings especially for deep lakes is to determine if the lake exhibits stratification. This can be monitored by temperature measurements from surface to bottom. Deep lakes normally exhibit thermal stratification known as epilimnion for the mixed warm surface layer, metalimnion for the middle layer that exhibits 1°C difference and the hypolimnion for the bottom layer. In most stratified lakes there is a well-oxygenated epilimnion and an anoxic hypolimnion with toxic gases. In this case temperature readings will show when the lake will overturn. This information is essential to prevent fishkills.

2.1.2 Dissolved oxygen (DO)

Next to temperature, the DO content of the water is probably the most commonly measured parameter. Oxygen is essential to almost all life so its shortage or absence limits the distribution of plants and animals.

The daily trend of oxygen concentration is essential in determining the highest and lowest levels in a body of water. The comfortable range (without stress to fish) of DO is 5.0 ppm and above. It is reported in the literature that good fish fauna are found in streams with DO over 5.0 ppm and that fish feed poorly and starve at 2.0 ppm DO concentration.

Analysis of DO in water is by the Winkler titrimetric method but recently electronic gadgets have been developed to measure DO continuously. Procedures may be found in standard reference books.

2.1.3 pH

pH is the measure of hydrogen ion concentration or acidity and alkalinity of water. The pH and its changes must be assessed since it may reflect biological activity and changes in natural chemistry of water. Ideal pH for fish growth is 6.3–9.0. Values lower than 4.5 and higher than 10 are detrimental to fish. pH is measured by a pH meter.

2.1.4 Ammonia

Ammonia is present generally as the end product of decomposition of nitrogenous organic matter. It may also be introduced from discharge of industrial wastes. It is highly soluble in water and is converted to the ammonium ion (NH4+) which is not toxic to fishes.

Ammonia is measured by the colorimetric method using indophenol blue. Ammonia concentration in water for fish culture should not exceed 1.0 ppm. Higher concentration decreases the ability of the hemoglobin to combine with DO of blood and hence fish suffocate.

2.1.5 Turbidity

Turbidity due to inorganic material such as silt reduces light penetration. This affects natural food production.

The Secchi disc (a white circular disc, 20 cm in diameter) is a practical gadget that determines the turbidity or transparency of water. A Secchi disc reading of more than 50 cm usually indicates a body of water with low natural food production.

Another instrument that measures turbidity is a turbidimeter. Results are expressed as turbidity units. Good fish population has been found at turbidity equivalent to approximately 1.2 units.

2.1.6 Toxic substances

There are a number of toxic elements that may exist in lethal concentration in water. These are: arsenic, chlorine, copper, cyanide and pesticides. Their analyses, however, need special techniques that may be resorted to if needed.

2.2 Biological productivity

Productivity is defined as the rate at which biological production occurs. Primary production means the formation of new biomass and is the most fundamental of ecological processes. Solar energy is transformed into chemical potential energy that can be utilized by all of the members of the food chain. The rate at which food is produced in an ecosystem determines to a great extent the amount of organisms that can exist there.

2.2.1 Methods of estimating primary productivity Standing crop method

Standing crop is that part of the production which is physically present in the system and does not include what is lost in respiration. This is determined by the following:

  1. Phytoplankton number and biomass determination using microscope. A biomass of more than 10 g/m3 is good for fish culture.

  2. Chlorophyll (plant pigment) measurement. Chlorophyll is extracted and read in a spectrophotometer. A rich water contains 5–100 mg/m3.

  3. The dry weight method - Harvesting of plankton is done and their dry weight is measured. Uptake of nutrients

This is an indirect method that estimates rate of production by measuring the elements (carbon dioxide, phosphorous, and nitrogen) removed in a given aquatic system and calculating the equivalent biological production from the absorbed amount. Dissolved oxygen method

In moderately to highly productive aquatic environments, it is feasible to measure dissolved oxygen produced in short-term incubations. Initial oxygen concentration is measured in the water sample before and after incubation in both light and dark bottles. The net and gross productivity is then calculated:

Net photosynthesis = Light bottle DO - Initial DO

Gross photosynthesis = Light bottle DO - Dark bottle DO Carbon - 14 method

This method is similar to the oxygen method except that the photosynthetic capacity of phytoplankton production is measured by the amount of fixed carbon. Lake water sample is added with a known strength of C14 and after incubation the uptake of C14 is related to the total uptake of carbon during this period. Impulses can be measured by a Geiger-Muller counter or a liquid scintillating spectrophotometer. The calculation of the assimilated carbon in milligrams per hour per cubic meter of water is:

As a general rule, measurement of water quality and productivity should be done at different depths but for shallow lakes (2–3 m) pooling of water samples can be done. Primary production of about 5 gmC/m2/day seems to be the minimum value for good fish growth.


In July 1970, the Laguna Lake Development Authority pioneered in fishpen culture by enclosing 38 hectares of a shallow cove in Barrio Looc, Cardona, Rizal. The idea of introducing milkfish (Chanos chanos) in fishpens was made possible by the following features of Laguna de Bay:

  1. The common economic species in Laguna Lake, the freshwater perch or Therapon plumbeus, the white goby or Glossogobius giurus, the freshwater catfish or Arius sp. and the snakehead or Ophiocephalus striatus are not true plankton feeders. Only Therapon approaches the closer link to the primary consumer group of fish by feeding on some diatoms and algae. Therefore, milkfish being a plankton feeder is an ideal species for culture in Laguna Lake.

  2. Laguna Lake exhibits a yearly occurrence of algal blooms especially in summer which indicates abundance of natural food. The average cell count per ml is about 100 000 or roughly equivalent to 30 g/m3 biomass. Primary productivity is 0.5–9 gC/m2/day.

  3. The lake has an average depth of about 3.0 m and the bottom is mostly muddy-silt, except in some parts of the East Bay where it is rocky and sandy, which makes construction of pens easy.

  4. The average monthly water temperature of the lake varies from 23.5 to 33°C.

  5. The water is generally mixed; thermal stratification may appear in short durations during the periods of low wind velocity and little water turbulence.

  6. The pH varies from 7.6 to 8.5 in summer. Although a peak of pH 10 was recorded during an algal bloom.

  7. The average concentration of DO varies from 5 to 10 ppm or 60–160% saturation. Highest fluctuation occurs during the summer months as a result of algal blooms and die-offs.

The early operation of the fishpen industry without typhoon damage and poaching was successful and highly profitable. An average yield of four tons per hectare per year (highest reported yield is ten tons per hectare) was recorded.

The early success of the fishpen operation has caused the proliferation of fishpens in all parts of the lake. The problem now is determining the carrying capacity of the lake. This needs at least an assessment of the annual phytoplankton biomass produced by the lake and the proper determination of conversion factor from algal biomass to fish flesh.

In this connection it is necessary to evaluate the ecological role of sea water intrusion in the lake. During periods of strong wind velocity, the lake being shallow has a high inorganic turbidity that limits natural food production. Density of plankton is very low. In the dry season, however, lake level falls below the mean sea level of Manila Bay so that during high tide inflow of seawater takes place. The seawater intrusion causes the inorganic turbidity to flocculate and settle to the bottom. This results in improved light penetration that stimulates the production of natural food. Thus, the backflow of saline water becomes indirectly an important factor that affects the natural food production in the lake.

The fishkill phenomenon in Laguna de Bay is a problem related to changing water quality conditions. During periods of calm weather condition, the lake stratifies for about two weeks or more depending on the prevailing climatic condition. This stratified condition causes a depletion of oxygen at depths below one meter suffocating the fish and resulting in mass mortality of fish.

It is necessary that a continuous ecological study be conducted on any lake for fishpen development for proper stock assessment and management.

Vicente N. Alferez


Pen and cage culture were first introduced in the country in 1965 by the Bureau of Fisheries and Aquatic Resources (BFAR) using common carp, “tawes” and goby (biyang puti) in the lakeshore of Laguna de Bay, Philippines. This was later followed by another set-up in the culture of tilapia in Sampaloc and Palakpakin lakes in San Pablo City, also in the Philippines. In 1970, an experimental fishpen for milkfish culture was constructed by the Laguna Lake Development Authority (LLDA) at Looc, Cardona, Rizal. At present, the Laguna de Bay has approximately 8 000 ha of fishpen in operation producing about 40 000 tons of milkfish yearly.

In 1979, the Philippines signed a loan agreement with the Asian Development Bank (AsDB) to finance a 2 500 ha fishpen development project to be reloaned to about 1 550 small fishermen families. It is estimated to produce 10.5 mt of bangus and 5.5 mt of tilapia yearly.

The Southern Philippines Development Authority is developing 400 ha for milkfish pen culture in Lake Buluan, Sultan Kudarat, Mindanao, Philippines. It is estimated to produce 3 850 mt yearly. The project is envisioned to benefit 1 152 families.

In Japan, pen and cage culture of octopus and yellow tail are well-developed industries. Other countries in Asia and Eastern Europe are in various stages of development in these aquaculture activities.

Undoubtedly, pen and cage systems, as used in the culture of finfishes, have attracted many developing countries, that it is high time that a systematic packaging of the various technologies being adapted be prepared. To this end, this lecture series on Pen and Cage culture of Finfish is very much welcomed.

1 Consulting Fishpen Engineer, LLDA-AsDB Fishpen Development Project. Consulting Engineer, Bio-Resources International, Inc.


The fishpen as developed in the Philippines consists of the enclosure net and the supporting framework. The enclosure net is simply a fence where the bottom edge is embedded about one meter into the mud and held up above water by the framework. The latter is made up of vertical poles closely arranged to form either a square, rectangular or circular configuration. Apart from these elements, certain changes have been evolved through the years. One of these is the attachment of a series of floats along the head rope of the enclosure net. Another innovation is the provision of barrier structures to protect the enclosure net from floating vegetation like the water hyacinth or other flotsam. The supporting framework has also been improved from one-side bracing to two-side bracing. In some instances, this framework design has been adopted for the barrier structure and a widely spaced supporting system is used instead to hold the enclosure net in shape.

The traditional materials used in fishpen construction are bamboos, wooden posts or both, for framework, and polyethylene or nylon netting for the enclosure net. Stones or concrete blocks are used as sinkers.

Another important element in the fishpen is the nursery compartment whose design and construction are similar to the pen enclosure itself. The size of the compartment is about ten percent of the total area of the pen. The net used, however, is either fixed permanently inside the pen or detachable.

Before going further, it is suggested that a standard definition of some terms be adopted. Many times, the term net pens and cages are being used to mean the same thing, when in fact, this should not be the case. Although the dictionary defines pen as enclosure, such as a cage, in aquaculture, the term pen refers to a fence-like structure made of plastic nets, bamboo matting, or steel wire mesh embedded into the mud bottom. It has no flooring nor any covering. While the term cage refers to a system whose configuration is that of an inverted mosquito net which may be made of plastic net or steel wire mesh. In terms of size, a pen ranges from 1/2 ha to 1 000 ha in area, while a cage ranges from one sq m to perhaps 1 000 sq m. The reason for this limitation in size is obvious. Firstly, quantity-wise for the same culture area, the pen requires less materials compared to a cage because of the absence of a flooring of the former. Secondly, construction methods are different. Thirdly, harvesting methods are different.

In summary, pen culture should be treated differently from cage culture.


In order to be successful in the planning and implementation of any fishpen project, certain design considerations are to be met. These considerations are presented in a form of a chart (Fig. 1) to show their inter-relationships with each other.

The flow chart indicates that prior to any preliminary design calculation of the system being considered, basic questions as to biological constraints, design limitations, and physical-environmental constraints have to be determined, in addition to the general information as to species, site location, timetable and life of system. The final selection of the design is dependent upon whether the project cost is within the means of the proponent and whether enough logistical support is available. Otherwise, the design will have to be toned down to meet these constraints.

3.1 Fishpen design

3.1.1 Design criteria

There are two basic criteria in the design of any structure. These are: the strength criterion in which a member or a structure resists a given force; and the rigidity or stiffness criterion in which the member sustains deformations due to the given force. A third criterion which is time dependent, is durability. Material selection plays an important role in the overall life of the system. Effects of wetting and drying, and excessive exposure to sunlight affects the durability of the materials.

3.1.2 Existing framework designs

As mentioned earlier, there are two basic framework systems adopted in Philippine fishpen designs (Fig. 2). Type I, as shown in the edge view, consists of vertical pole and a bracing fastened near the top. The bracing is effective when the direction of the forces acting on the whole structure is opposite to it. It is less effective in the other direction because of possible uprooting.

Type II is an improvement of Type I since it has now two bracings, one on each side of the pen. There is difficulty, however, in the harvesting of the stock when the drag seine (pukot) is used. In addition, it would be difficult to prevent escaping of the fish when the water level rises above the intersection of the braces as the enclosure net is attached under the bracing.

To solve this problem, a third type was evolved. Type III utilizes two framework systems. One acts as the barrier structure which may be single or double-braced. The other acts as the supporting system for the enclosure net to maintain its shape.

The main anchorage system of all three types is their being embedded deep into the mud bottom creating a fixed-support condition which makes the framework structure very stable. However, in some cases, the mud bottom is not so deep or the embedment is not done properly so that the fixed-support condition does not occur. When this happens, the constant swaying of the structure due to the external forces will tend to loosen its foothold in the mud.

3.1.3 Innovative framework systems

Three framework systems are presented in Fig. 3: (1) triangular framework; (2) rectangular framework; and (3) skewed framework. Each of these types has its own advantages and disadvantages described as follows:

(i) Triangular framework

The system lends itself to the traditional system in terms of shape. One difference is the horizontal member connecting the vertical and bracing members. With this additional member, the whole framework becomes statically stable and indeterminate to the first degree due to an extra support. This framework system may not be attractive to fish farmers because of the added cost of netting due to its slanting position. Construction cost is relatively cheaper.

(ii) Rectangular framework

The system is basically a portal system although the joints are considered hinges. Portal action is provided for by the bracing. It is statically stable and determinate. It has the advantage over the triangular framework in that the netting is vertical. Harvesting of the stocks is relatively easy. Provisions of a catwalk can be made at the top of the pen. The whole pen made of this type of framework can therefore be guarded or secured by means of foot patrols instead of water patrols. Construction cost is only a bit higher than that of the triangular framework.

(iii) Skewed framework

The system is similar to the rectangular framework. However, the positioning of the basic framework is skewed to the center line of the pen to provide lateral support not only transversely but also longitudinally thus, minimizing on braces. It is also statically stable and determinate. Its advantages are similar to the rectangular framework. Construction cost is about the same as that of the triangular framework.

Selection of a particular framework system largely depends on the cost, its functionality and ease of construction. The cost savings obtained in a triangular framework over the others may be offset by the cost of extra netting to be provided in the slanting position of the net. Also, functional requirements suggest conversion of the top of the rectangular or skewed framework into a catwalk.

As compared to the traditional framework system, these are more stable, rigid, and can stand alone as basic structures. Cost-wise, these are more expensive but the difference in initial cost is offset by durability and strength.

In any event the use of these systems is not limited to bamboo. Other materials like G.I. pipes and timber piles may be used except that the cost is prohibitive.

3.2 Forces sustained by fishpens

In designing structures, it is important that forces are properly determined. These forces are either man-made or natural. They are induced either laterally or vertically. In fishpen structures, lateral forces are either caused by wind, waves, or water current. These natural phenomena, aside from their inherent characteristics, also cause floating vegetation and other flotsam to drift. Vertical loads are live loads which are almost insignificant and therefore may not be considered.

3.2.1 Wind force

  1. Acting on a solid structure

    Fw = 0.946 AV2

    whereFw = wind force (N), N= .102 kg force
      = .22 lb force
     A = projected area of the solid perpendicular to wind direction (m2)
     V = wind velocity (m/s) 
  2. Acting on a fish net

    Fw = 0.182 AV2

    whereFw =wind force (N)
     A =projected area of the net (net area of ropes and bars only) to a plane perpendicular to the wind direction (m2)
     V =wind velocity (m/s)

    Pw = 1/2 k ρ V2

    where Pw =wind pressure, N/m2 
    ρ =density of air kg/m3 
    V =air velocity, m/s 
    k =resistance coefficient= (1-B)/B2
    B =blockage coefficient= 1-d/L2
    d =twine diameter (m) 
    L =nominal mesh size 

3.2.2 Wave force

  1. Horizontal and vertical forces on a net structure

    Fh = 2.15 Vh

    Fv = 1.8 Vh

    where Fh =horizontal force (N)
    Fv =vertical force (N)
    Vh =maximum horizontal water particle velocity in a wave (m/s)
    Vv =maximum vertical water particle velocity in a wave (m/s)

3.2.3 Current force

  1. On a net structure due to flow at right angles to the net (Method 1)

    Fc = 4.9 ρ V2 A Cd

    where Fc =force applied to net by current, N
    Cd =coefficient of drag of mesh
    ρ =density of water, kg/m3
    V =current velocity, m/s
    A =projected area of net ropes/bar = 2 ad, m2
    a =nominal mesh size, m
    d =diameter of net twine/bar, m
    for a knotted netCd = 1 + 3.77 (d/a) + 9.37 (d/a)2
    for a knotless netCd = 1 + 2.73 (d/a) + 3.12 (d/a)2
  2. Net drag (Method 2)

    Dpanel = (CD90° sin × 0.005) S 1/2 ρ V2Asurface

    where CD90°
    Ap =(AkK) + (Abb)= area of panel
    Ak =1/4 π Dk2= cross-sectional area of knot
    Ab =DbLb= area of bar
    x =angle of attack (direction of current with respect to net

3.3 Materials and construction

The effects of typhoons, and vegetation drifts can be minimized not only by good design but also by proper selection of materials, good construction methods and a lot of common sense. The latter can be best appreciated by proper selection of shape like a circular configuration which is best for any wind direction or a square provided its diagonal is parallel to the prevalent/most dominant wind directions. Between a rectangle and a square, the latter has a shorter perimeter and therefore less expensive for the same structural framework and netting.

Depending on the magnitude of the project and availability of resources, fishpen sizes considered small-scale are 2 ha to 10 ha. For large-scale projects, the size could range from 50 ha or more.

3.3.1 Materials for construction

Efforts should be geared toward the use of indigenous as well as locally available materials whenever possible to reduce the cost of the fishpen.

For enclosing the fish stock, the use of synthetic fiber material for netting is becoming more and more popular compared to natural fibers, because the latter rot in water easily. Other netting products such as G.I. wire mesh or steel expanded wire mesh are very expensive and easily corroded.

The most commonly used synthetic fibers are nylon, polyester, polyethylene, and polypropylene. There are factors that must be considered in the selection of netting materials such as economy, strength, and durability in its resistance to deterioration by solar radiation (Table 1).

Netting yarns and netting must be clearly specified according to international or national standards when placing an order to a manufacturer. The following physical features must be indicated in purchasing netting: kind and type of fiber; size of netting yarn; whether twisted or braided; whether knotted or knotless; size of mesh; size of netting; direction of stretching; and after treatment.

For framework structure, many kinds of materials can be used such as bamboo, wooden poles, G.I. pipes and PVC pipes to name a few. Bamboo appears to be the most suitable as it is the cheapest, more resilient and easily available. Its major disadvantage, as in other natural products, is its susceptibility to fungi attack in addition to deterioration due to constant wetting and drying. Another disadvantage is the very unreliable supply.

There are several species of bamboo that can be used in fishpen construction, foremost of which is the spiny bamboo or Bambusa blumeana. Other species are Giganthocloa levis or “kawayang bo-o”, “botong” (Visaya), “boho” (Tagalog); Dendrocalamus merrillianus or “bayog” (Ilocos), “kawayanbayog” (Pangasinan).

For fastening/tying the various members to form a composite structure, polyropes (PP or PE), rubber tire strips, G.I. wire, steel plate connectors and nylon monofilament are used.

3.3.2 Construction of fishpen nets

First of all, the perimeter of the fishpen is computed and the depth of water and mud is measured. Historical data of the water levels is also obtained from either the Weather Bureau or from old folks residing in the vicinity who have first hand information on flood levels over the years.

Once these are available, the net dimensions are next computed and cut. The following formulas can be used:

For length of netting:

where r= hanging ratio (usually 0.3 for best results to obtain a stretch of 70% of mesh size
Ls= length of stretched netting, m
Ld= desired length, m

For depth of net:

where D= desired depth, mm
Ds= depth of stretched netting, mm

More often, the length is determined in terms of stretched length in meters. Whereas the depth of the net is expressed in terms of number of meshes called mesh depths (MD). A mesh is that portion of the netting formed by the bars or twines of the netting. The depth in meters may be converted into number of meshes by the formula:

where MD= total number of meshes
ml= mesh length, obtained by measuring the distance between two opposite knots or bar intersections, mm

Before assembling the nets, make sure that a working area measuring not less than 20 m by 50 m is available. It must be a relatively flat ground, and free of twigs, bushes and debris.

A typical net assembly and preparation used in the LLDA-AsDB Fishpen Development Project is presented as an example.

(i) Enclosure net assembly

The enclosure net is made up of two materials; namely, PES and PE. Fifty mesh depths (MD) of PES is longitudinally connected to a 350 MD PE by braiding a half mesh using the single weaver's knot (Fig. 6).

The following steps may be followed in assembling the enclosure net:

Step 1 -Unroll or unfold the nets and insert a 6 mm Ø PE rope through the first row of meshes (Fig. 7). The length of the rope inserted must be equal to one-fourth the perimeter of the pen plus 2 m.
Step 2 -Fasten the PE rope by stitching a 1 mm Ø PES twine using a clove hitch secured with an overhand knot (CHOK) at 47 mm on centers (see inset of Fig. 9 for CHOK).
Step 3 -After doing steps 1 and 2 for both the PES and PE nets, they are rolled separately until a 50 m long free end is left (Fig. 10).
Step 4 -Six sets of bamboo pegs spaced at 10 m on center are driven from the free end. The pegs in each set are separated 6.50 m from each other (Fig. 10).
Step 5 -Attach the edge with the rope of both nets to the pegs and stretch tightly the rope securing the ends at the outer pegs. (Fig. 10).
Step 6 -Stretch the nets so that the free edges of both barely touch each other. Maintaining the stretched position is not a problem since the nets are coated with stiffening agents.
Step 7 -Starting from the free end, the edges are connected by braiding a half mesh using a single weaver's knot (Fig. 8).

Upon reaching the rolled end of the nets, steps 3, 4, 5, 6 and 7 are repeated until the whole section is connected.

(ii) Freeboard net assembly

Steps 1 and 2 of enclosure net assembly are used except that both second row of meshes from the edges of the net are inserted with a 6 mm Ø rope and stitched with a CHOK spaced 47 mm at every intersection of two bars. (Fig. 9).

(iii) Barrier net assembly

Like the freeboard net assembly, steps 1 and 2 are used except that the rope used is 10 mm Ø and the stitching is spaced at 105 mm, respectively. (Fig. 9).

(iv) Nursery net assembly

Having a finer mesh, the insertion of a 6 mm Ø rope through the meshes requires a tapered tool which forces the mesh to enlarge allowing the rope to pass. This could be made of bamboo. The rope is inserted about 20 mm from the edge of the net. Since the net length is stretched, the stitching must be such that the net so stitched is 30 percent longer than the spacing of the CHOK (Fig. 12).

(v) Floats and sinkers attachment

The attachment of the floats is done after connecting the free-board net and the PES enclosure net. The sinkers are attached on site during installation of the nets.

The resulting pen enclosure assembly is shown in Fig. 12. Tables 2, 3 and 4 show additional information on the LLDA-AsDB fishpens.

(vi) Framework preparation and construction

Since there are many kinds of materials that can be used for fishpen framework, discussion will be limited to the use of bamboo as it is the most economical and readily available.

Prior to installation, the bamboo poles must be cleaned of sharp edges of the nodes to avoid damage to the net. They must also be slotted at the node diaphragm either by the use of chisel removing the diaphragm at the nodes from the outside (Fig. 13). The size of the bamboo poles must not be less than 10 cm diameter at the trunk and 3 cm at the tip and 10–12 m long. It is not advisable to use young bamboo poles even if they meet the size specification as this will easily deteriorate in water.

The bamboo poles will be erected by means of an erection guide (Fig. 15). A corner of the module shall first be located. A string shall be used to align the first set of poles. Using the erection guide, the 2nd, 3rd, 4th pole shall be driven into the mud. This must be followed by fastening the longitudinal and transverse horizontal stays to prevent misalignment. The next set of poles shall be erected by transferring the guide to the next position. This shall be done until the last pole on that side of the pen being worked on is completed. The bracings shall be installed after the third transfer of the guide to avoid overcrowding of workers in the same area.

Two teams will be employed. One team of three to four persons shall take care of the driving and the other team also of the same number shall take care of fastening the horizontal stays as well as the bracings.

When shallow mud strata is encountered, an improvised anchorage system to increase mud foothold of the bamboo pole may be used (Fig. 14).

After all these activities shall have been accomplished, the overall success of any fishpen project can only be achieved by proper operation and maintenance. Constant and periodic inspection of the fishpen nets and framework and their immediate repair when necessary should not be neglected.

Table 1. Effects of various factors on commonly used netting materials
FactorsNylon (PA)Polyester (PES)Polyethylene (PE)Polypropylene (PP)
Effects of ageVirtually noneVirtually noneVirtually noneVirtually none
Effects of sunlightLoss of strength on prolonged exposureOnly slight loss of strength on prolonged exposureLoss of strength after prolonged exposureSlight loss of strength after prolonged exposure
Effects of chemicalFormic acid with concentration of about 80% will dissolve the fiberResistance of a high orderRemarkable resistance to acids, solvents, organic saltsRemarkable resistance
Resistance to alkaliOutstandingOnly fair resistanceRemarkable resistanceRemarkable resistance
Resistance to fungi and bacteriaResistance to attack of microorganismsResistantResistantResistant
Resistance to insectsNo known instanceResistantResistantResistant
Resistance to abrasionHighest resistance to abrasionRanks second to nylon onlyVery goodVery high
Wet condition10% loss of strengthAs strong as nylon when immersed 5% increase in strength
Water absorption65% RH - 4.8% 100% RH - 7–9%65% RH - 0.4%
100% RH - 0.5%
Practically nonePractically none
Table 2. Perimeter and stretched length of net
Pen Size Pen enclosure Barrier Nursery
Perimeter Stretched length of net Perimeter Stretched length of net Perimeter Stretched length of net
2.5 ha 633 823 712 926 200 260
5.0 ha 894 1 163 980 1 274 283 368
10 ha 1 265 1 645 1 344 1 747 400 520

Table 3. Typical net dimensions and sizes
Type of netMesh length
No. of knots per 6"Size of yarnMDNominal hanging depth
Enclosure net - PES2214 K28 tex × 39 fil500.85
Enclosure net - PE2214 K43 tex × 15 fil3506.00
Barrier net - PES1523 K28 tex × 120 fil253.00
Freeboard - PES517 K28 tex × 36 fil271.0
Nursery - PE1031 K43 tex × 3 fil6004.5
Cage nets - PES6.547 K28 tex × 85002.5
Cage nets - PES6.547 K28 tex × 88504.25

Table 4. Length of rope
Pen sizePerimeter
1 m
Enclosure net
Length of rope per section
+ 2 m
Freeboard net rope
Length per section
+ 2 m
Barrier perimeterBarrier net rope length per section
+ 2 m
Float rope length
+ 2 m
Nursery perimeterNursery rope length
+ 2 m
2.5 ha633160160712180160200202
101 2653183181 344338318400402

Fig. 1

Fig. 1. Pen culture system design flow chart

Fig. 2

Type II. Double-side Bracing

Fig. 2. Schematic diagram of traditional fishpens and forces of members under load

Fig. 3

Fig. 3. Innovative framework systems

Fig. 4

Fig. 4. Indicative design for fishpen wall as defined by LLDA

Fig. 5

Fig. 5. A floating fish net barrier design for providing large enclosures for milkfish farming in Laguna de Bay (Milne, 1974)

Fig. 6

Fig. 6. Single sheet bend joint PES to PE NET

Fig. 7

Fig. 7. Headrope of enclosure net.

Fig. 8

Fig. 8. Freeboard and enclosure net connection.

Fig. 9

Fig. 9. Head and foot rope installation for barrier net

Fig. 10

Fig. 10. Enclosure net connection

Fig. 11

Fig. 11. Nursery net assembly

Fig. 12


Fig. 13


Fig. 14


Fig. 15

Fig. 15. Pole erection diagram

R. D. Guerrero III


Fishpens are usually built in shallow lakes with fertile waters. Much of the nutrients required for fish growth in pens is derived from natural food. The choice of species for stocking in commercial pens is largely dictated by two basic requirements: (1) the adaptability of the species in confinement to the lake conditions, and (2) the ability of the species to take advantage of the lake's productivity. Aside from biological and economic factors for species selection, the availability of fish seeds for stocking is also a major consideration in the operation of fishpens.

The different species cultured in the fishpens of Laguna de Bay and the sources of fish seeds are discussed in this paper.


The general criteria applied for the selection of fishes for pond culture also apply for pens. The desired features of the species are: (1) fast growth, (2) good consumer acceptance, (3) high tolerance to a wide range of environmental conditions, (4) resistance to disease, and (5) ease of culture or management. In the Philippines, the milkfish, tilapias and carps have been found suitable for pen culture.

2.1 Milkfish

The milkfish (Chanos chanos) is a euryhaline species native to the Philippines and other countries in the Pacific basin. It is extensively cultured in brackishwater ponds throughout, the country and in the Laguna de Bay fishpens.

The milkfish is an herbivore that feeds on benthos and plankton. In Laguna de Bay, the bulk of its diet consists of phytoplankton (e.g., diatoms, green and blue-green algae).

The growth rate of milkfish is in the range of 1–3 g/fish/day depending on management and time of the year. The fish is relatively hardy and has no known important disease and parasite.

1 Consultant, Laguna de Bay Fishpen Development Project, Los Baos, Laguna, Philippines.

Fry of milkfish are available in the wild in most months of the year. Collection of the fry and the production of fingerlings are major industries in the Philippines. Success in the induced spawning of milkfish breeders (sabalo) and the spontaneous maturation of the species in captivity have been attained by the SEAFDEC Aquaculture Department. Techniques, however, for hatchery management are still being refined.

2.2 Tilapias

Although not commonly cultured in pens at present, tilapias have been found to be a good substitute for milkfish by many fishpen operators. The Nile tilapia (Tilapia nilotica), introduced in 1972, has gained much popularity over the Mozambique tilapia (Tilapia mossambica) mainly because of its faster growth. It is not unusual to find 2–4 kg/size Nile tilapia cought in fishpens.

The Nile tilapia is an efficient phytoplankton feeder. It has the unique ability of digesting blue-green algae by acid action in its stomach. The fish also breeds readily in the lake throughout the year.

Tilapias can tolerate as low as 0.1 mg/1 concentration of dissolved oxygen in the environment. They survive within the pH range of 3.5–12. Like milkfish, the Nile tilapia has no serious parasite and disease problem.

One problem in the culture of tilapia in fishpens is difficulty in harvesting. The fish burrows into the mud bottom and avoids capture. Improvement of the harvesting methods is therefore needed.

2.3 Carps

Two imported carp species have become established in Laguna de Bay. These species are the common carp (Cyprinus carpio) and the Crucian carp (Carassius carassius). No deliberate stocking of the pens for carps is done. The fishes grow to sizes big enough to get caught in pens. In recent years, a few hatcheries have produced fingerlings of silver carp (Hypopthal-michthys molitrix) and bighead (Aristichthys nobilis). As a result, culture of these fishes in fishpens to a limited extent has ensued.

The common carp is a bottom feeder while the silver carp and bighead are plankton-feeders. Growth rates of the species in the lake are very encouraging. The survival of the fishes is good.

Carps, unfortunately, are less preferred by Filipino consumers compared to milkfish and tilapia. The price in the market for carps is usually only half the price for the latter species.


The supply of fish seeds for stocking in pens must be assured in terms of quality and quantity for commercial operations. The sources or suppliers should therefore provide the needed volume and kind of fry or fingerlings.

For milkfish seeds, the main sources of supply are the brackishwater nurseries in the towns bordering Manila Bay. The fingerlings transported to the fishpens mainly by live fish boats via the Pasig River have been reared from fry gathered from the wild in many coastal areas of the country.

Because of great losses incurred during transport and acclimation of the fingerlings from brackishwater to freshwater, efforts to rear milkfish fry to fingerlings in freshwater ponds and net cages in the lake have been attempted by the private sector. From available information, it appears that milkfish fingerling production in freshwater nurseries is a profitable enterprise.

Tilapia seeds are produced by fishpen operators in net cages beside the pens or procured from freshwater nursery operators. The fingerlings are transported to the fishpen site in plastic bags with oxygenated water.

A few hatcheries in the country produce carp fingerlings. The need for special skills in the induced spawning of the Chinese carps, with the exception of the common carp, has limited production of their fingerlings only to one government hatchery and a private farm.

Andres M. Mane


Laguna de Bay with an area of 90 000 ha is located a few kilometers south of Metro Manila. It is the only lake known in the Philippines or probably in Southeast Asia where pen culture of fish has been extensively developed.

In 1980, there were about 7 000 ha of developed fishpens estimated to have produced from 25 000–30 000 tons of milkfish valued at about 200–250 million.

The fishpen industry in the lake is still expanding in view of the interest given to it by the Philippine Government and the private sector.


The culture of fish in pens in Laguna de Bay was first attempted by the Philippine Fisheries Commission in 1965 using various species of freshwater fishes. The project did not make much headway and was finally abandoned.

In 1967, small-scale commercial fishpen culture was started in Sampaloc Lake, San Pablo City, after a consultation meeting between the City Mayor, a group of residents around the lake, and representatives of the Philippine Fisheries Commission. It was decided that ten fishpen modules, each with an area of 2 400 sq m, be constructed. The culture of milkfish, tilapia and carps was undertaken. The culture of tilapia proved very successful to the extent that it is still being continued to the present. The culture of the other species was abandoned.

The biggest development in the culture of fish in pens took place in Laguna de Bay after the Laguna Lake Development Authority (LLDA) had demonstarted the profitability of the venture in its Fishery Station at Cardona, Rizal in 1970. It was established that the production of milkfish in fishpens was more than four (4) times that of brackishwater fishponds.

1 Former Commissioner, Philippine Fisheries Commission and presently Project Advisor of the Laguna de Bay Fishpen Development Project, LLDA, Los Baos, Laguna. Philippines.

As a result of this demonstration, milkfish pen construction proceeded by leaps and bounds although it suffered a number of setbacks due to destruction/damages caused by typhoons, especially in the years 1974, 1976 and 1978.


The business of culturing milkfish in pens is a very risky venture in view of the hazards brought to bear on it by uncontrollable factors including harsh weather and climatic conditions, rapid changes in the ecology of the lake inimical to the life of fish, and socio-economic problems.

However, properly managed, it is sure to pay dividends. In fact the fishpen operators in the lake had evolved management systems for fishpens which make them confident and feel secure in their business. These are discussed subsequently.

3.1 Location of pens

The areas in the lake where the fishpen is to be constructed are selected very carefully as the success of milkfish culture depends on it to a great extent. The following criteria are used in selecting the site for fishpens:

  1. Should preferably be located in sheltered areas where the effect of strong winds and typhoons is minimal;

  2. The bottom mud is firm so that the bamboo and wooden poles supporting the pen framework can be driven deep enough in order to stand as much as possible rigorous weather conditions.

  3. Should be in a place with sufficient water current that will bring into the pen natural food organism and water laden with dissolved oxygen;

  4. Should be outside the navigation routes and path of drifting water hyacinths and other floatsam;

  5. Should be within the fishpen belt established by the LLDA; and

  6. Should be easily accessible from land.

Most fishermen know more or less the best sites for fishpens. However, preliminary surveys should be undertaken before a final decision is made.

3.2 Fishpen construction

This subject is discussed in detail in a separate lecture on fishpen construction. However, a few statements are here given which has relevance to the management of the pen culture units.

3.2.1 Time of construction

The construction and setting of pens in water is usually undertaken in the months of March to June when there is the prevalence of calm and gentle winds. In other months of the year, violent winds and stormy weather occur making it difficult and expensive to construct the pens.

3.2.2 Fishpen materials

The success of the culture of fish in pens depends on how the fish can be contained in them. This will need a very careful selection of materials that can stand harsh weather and climatic conditions and for economic considerations.

The common materials used for fishpen posts is the bamboo. There are several species of bamboo but the fishpen operators use the spiny bamboo (Bambusa spinosa). Because of its rigidity, it lasts long in water. However, proper selection should be made to see to it that only mature bamboos (more than one year old) are used. Young and immature bambooes last only for about a year.

Lately, wood posts and trunks of a plam tree species (anahaw) have been used interspersed with the bamboo to give more strength to the pen framework. Only wood from the mature trees are used.

The fencing materials used are the synthetic nets (polyethylene, nylon and kuralon). As there are no regulations prescribing the quality of these nets in the market, damaged or weak nets are often mixed with good quality nets which make the pen fence unstable. The weak and damaged nets wear easily resulting in holes and other avenues for the fish to escape. Rigid inspection of the nets purchased becomes necessary and a must.

The government regulation prescribing the holdings of fishpen operators (owners) is as follows: (1) five hectares for individuals, and (2) fifty hectares for partnership, association, cooperatives and corporations.

Various shapes of the fishpen module are to be found in the lake. The fishpen shape can be circular, polygonal or rectangular. The shape of the pen module that best fits the culture of fish has not yet been studied and standardized.

The fishpen module consists of two types of compartments: (1) the nursery compartment and (2) the growout compartment. The netting materials of the nursery compartments are of fine mesh which would not allow small milkfish fingerlings to pass through. It is a mistake of some fishpen operators to use wide mesh nets for the nursery units which results in the escape of fingerlings and the cause of big losses in the business operations. The nets of the growout compartments are of wider meshes to contain the fingerlings after they have been released from the nursery compartment. Using bigger mesh nets allow easy entrance of fish food into the fishpen.

3.3 Culturing of fish in the pen compartments

3.3.1 The pre-rearing of seed stock

The pre-rearing of milkfish seeds is mainly a land-based operation. This is a well-established industry in Malabon, Metro Manila and in towns of Bulacan Province bordering Manila Bay. Almost all the milkfish seeds of the pens in the Laguna de Bay come from these places.

The season for the production of milkfish seeds is from the months of March to September with the peak of production in May and June. The fry used for seed production comes from almost all places in the Philippines with sandy shorelines. The fry makes its appearance as early as the later part of February and lasts up to August or the early part of September.

About 300 million fry are needed every year to stock the fishpens of Laguna de Bay.

The nursery ponds for rearing milkfish fry to fingerlings range in size from 200 to 1 000 sq m. The natural food of the fish is first grown in the ponds before they are stocked with fry.

The nursery ponds are first drained fry to expose the surface to sunshine until the soil becomes sunbaked. Small amounts of sea water is then admitted just to make the soil water soaked. Fertilizer (e.g., chicken manure) is added and later tobacco dust is broadcast on the surface of the soil to kill the predators. When the growth of the plankton organisms has covered the entire soil surface of the ponds, the depth of water is increased to about 2 ft and more food of fish is produced. At this point the ponds are ready to receive the fry for rearing to fingerling sizes.

The milkfish fry coming from places like Mindanao and the Visayas are transported by plane in plastic bags with oxygenated water contained in styrofoam boxes. These are consigned to fry dealers in Malabon and Bulacan from whom the nursery operators obtain their fry needs. Fry coming from Luzon are usually transported by land vehicles.

The fry are reared in the nursery ponds from 21 to 30 days after which time they grow the fingerlings with sizes from 2–1/2 to 3 inches long that are ready for stocking in fishpens.

3.4 Stocking fishpens with fingerlings

3.4.1 Time of stocking

The time to stock fishpens requires a well considered decision on the part of the operator. Wrong timing may lead to big losses/setbacks in the production of fish.

The best time to stock fishpens is during the months of March to June which is the best period for rearing the fish. This period coincides with the occurrence of highest abundance of natural fish food (phytoplankton and zooplankton). The temperature of water is high -30–33°C favouring fast growth of fish. Stocking fish in these months would enable the fish to grow to marketable size and be harvested before the onset of the typhoon season (September-October) which is generally avoided to assure good fish harvest.

Late stocking in the months of July and August would make the rearing of fish pass through the typhoon season which is very risky as the fishpens most often suffer damages/destruction that enable the fish to escape. The rearing of fish will go through the northeast monsoon season (November to January) when strong winds of long duration prevail, making the water in the lake turbid or very muddy. Production of natural food in these months is at its lowest and together with the low temperature of the water (as low as 23°C) brought about by the cold weather season retards the growth of the fish. Thus, the rearing period is extended to about eight or more months.

3.5 Procurement and transport of fish fingerlings

At the start of the fingerling season, the price of the fish seeds is quite high due to competitive bidding of fishpen operators to enable them to catch up with the best period in culturing fish in the pens. Some operators have to advance money (before the fingerling season) to be assured that they get their seed fish on time.

Negotiation for payment of the fingerlings is made before the delivery. A day before the actual procurement of the fish seeds, the nursery operator concentrates them in a catching pond prior to counting. The fish is placed on a hanging net (bitinan) from where a sample is then taken and placed in a basin partially filled with water and then counted one by one. The total fish counted is the basis for the number of scoops to be made without anymore counting the fish in them to cover the amount of fish purchased.

Fish seeds are usually transported from the pond nurseries to the fishpens by means of live fish boats. These boats are partially filled with clean sea water before receiving the fish seed from the ponds after counting. Transporting the fish with the use of live fish boat is done during calm days in order to lessen the injuries and stresses on them. Transporting the fish during rough weather results in high mortalities. It is not uncommon to realize from 50–60 percent mortalities after stocking them in the pen when transported during unfavourable weather conditions. Transport of fish is also done using land vehicles (trucks, jeeps, etc.). The fish seeds are placed in plastic bags with oxygenated water and contained in buri bags. They are taken to the nearest spot where the pen is located and transhipped by means of motorized bancas (dugouts).

3.6 Stocking and rearing fingerlings in the nursery compartment of the pen

The nursery compartment is inspected for any damage or weak nets to prepare it to receive the fingerlings. The predator fishes are removed by seining and gill netting. Among these predators are the snakehead (Ophicephalus striatus) and the catfish (Clarias batrachus) which are trapped in fencing the nursery.

The live fish boat containing the fingerlings is anchored near the nursery for about 20 minutes to acclimatize fish by replacing water in the boat with the lake water.

The fingerlings are then concentrated in a net inside the boat by means of pail and poured inside the nursery.

The fish seed stocked in the nursery compartment are fed twice a day with rice bran until they become active and forage freely for the natural food.

The rearing period of fish seed in the nursery is about one month when they have grown to a size big enough (about 5 inches in length so as not to pass through the bigger meshes or the net of the grow-out compartment.

3.7 Culture of fish in the grow-out compartment

Before the fingerlings are released from the nursery, the grow-out compartment is cleaned thoroughly of predator fishes. The same method used in the cleaning of the nursery is applied. The fence nets are carefully checked for holes and other damaged parts that will allow the escape of the fish.

Release of the fingerlings from the grow-out compartment is effected by lowering the side of the nursery net until all the fish have gone out.

It takes about four months of rearing for the fish to reach the marketable size (4–5 pieces to a kilo). The operator may choose to allow the fish to grow bigger (2–3 pieces) before marketing the produce in which case the rearing period is extended to about 5–6 months.

3.8 Maintenance and repair of fishpen

The fishpen has to be well maintained and immediate repairs have to be done when needed in order to contain the fish being cultured. Improper/ inadequate maintenance has been the cause of tremendous losses in fishpen business. The pens are exposed to harsh conditions of weather and climate and other factors that are destructive so that full attention should be given for its maintenance and repair.

For proper maintenance, infrastructure facilities and equipment needed should be provided. These include among others the caretaker's house and watch houses for laborers, motorized banca, lighting equipment, diving equipment and tools and materials needed for repair work.

Frequent inspection is required to look for damaged parts of the pen especially the portion of the net underwater. Destroyed portions and even small holes on the net will serve as avenues for fish cultured to escape. Immediate repair/mending are necessary to prevent the fish from going out.

After each typhoon and long duration of strong winds, parts of fishpen get destroyed as the big waves generated push the water hyacinths and other floatsam to the nets and with continuous abrasion force the net to break.

Immediate repair should be done in order to save as much fish inside the pen as possible.

Constant patrol at nights should be done by rounding the pen to prevent poachers from pilfering the fish. Oftentimes these poachers, slash the nets, open and catch the escaping fish. These openings should immediately be closed when detected. Spotlights and flashlights are important equipment in patrolling.

After a few croppings (one or more years), the portion of the net that is within the range of the rise and fall of the water level of the lake gets brittle or worn out. These should be cut and changed by new ones. These can be done immediately after harvest by repairing the net in water or on land.

The ultimate need for the proper maintenance and repair of fishpens are competent men who have the experience and skill in this type of work.



When fishkills in pens occur, the fishfarmer affected may suffer heavy losses. This phenomenon happens when water quality deteriorates to a level inimical to fish, or when an epizootic occurs.

This paper will analyze the different factors involved in fishkills in pens and some preventive measures that may be practiced in order to prevent fishkills.


2.1 Physico-chemical factors

2.1.1 Water quality

The nature of water quality parameters such as DO, CO2, NH3, H2S and pH affect the growth and survival of fish.

Dissolved oxygen

The optimum dissolved oxygen requirements of fish are 5 mg/1 and more. Fish may survive with low oxygen content of the water, however, growth rate is adversely affected and the fish become susceptible to bacterial infection.

Carbon dioxide

The carbon dioxide level usually fluctuates from 0 mg/1 to 5 mg/1. Higher concentrations of CO2 may be tolerated provided DO concentration is high.


Unionized ammonia (NH3) becomes more toxic when DO concentration is low. Toxic levels of NH3 are from 0.6–2.0 mg/1.

1 Assistant Professor, College of Inland Fisheries, Central Luzon State University, Nueva Ecija, Philippines.

Hydrogen sulfide

This is highly toxic to fish and sudden exposure to high concentrations may cause mortality or poor growth rate if exposure is extended.


The acid and alkaline death points for most fishes are approximately pH 4 and pH 11, respectively.

2.1.2 Pesticides

Most pesticides are toxic to fish. Mortality of fish usually occurs at pesticide doses of 5–100 mg/1.

2.1.3 Physical factors

Overturns or thermal destratification

During cold months or the rainy season, the oxygen deficient hypolimnetic water mixes with epilimnetic water causing an anoxic condition. Overturns also occur during cloudy and windy periods when photosynthetic activity is almost nil.

Phytoplankton die-offs

This is due to the sudden death of phytoplankton (e.g. Microcystis and Anabaena) followed by rapid decomposition. Die-offs usually occur when the thick blooms of blue-green algae on the surface are overturned. Do concentration during the period sometimes falls to as low as 0 ml/1.


The death of large amounts of vegetation in the lake (e.g., Eichornia crassipes) may result in low DO concentration because of decomposition.

2.1.4 Measures to prevent fishkills

Identification of the problem

Visual survey of water - When the green colour of the water changes to gray a die-off may be occurring. Scum appearing on the surface is another indication of low DO level. Fishes gasp for air on the water surface.

Secchi disc visibility - During phytoplankton blooms the visibility is less than 30 cm.

Odor of the water - Decaying organic matter gives off H2S and other noxious gases.

Measures to be used

Aeration - use of mechanical aerators or pumpboats

Early harvest of fish - the fish are harvested in pens before the occurrence of fishkills.

2.2 Biological factors

2.2.1 Bacterial infection

Pseudomonas and Aeromonas bacteria are known to cause mass fish mortality in ponds. They are also present in fishpens with very low DO concentration.

2.2.2 Parasites

External parasites such as anchor worms and protozoans are found in fishes but usually do not cause mass mortalities. However, the appearance of the fish may be affected and their market value decreased.

Andres M. Mane


Harvesting, post-harvest technology and marketing of the fish produced in pens are very important undertakings which if not done properly, could result in poor financial returns from production efforts and investments.

The fish in the pen is as good as fish in the can through right timing and proper harvesting, good care and handling of the harvested fish and following the right procedure of marketing. These operations are quite established in the fishpen industry and should be known to investors or would-be investors in order to get the maximum benefit from their investment.

1 Former Commissioner, Philippine Fisheries Commission and presently Project Advisor to the Laguna de Bay Fishpen Development Project, LLDA, Los Baos, Laguna, Philippines.


2.1 Time to harvest

The fish can be harvested for the market when they have attained a size of about 100 g each (10 to a kilo). The common sizes of fish reaching the market range from 200 to 500 g per fish (5 to 2 fish a kilo). Bigger ones, one kilo or more, are a rarity.

There is a decided advantage in marketing bigger fishes as bigger returns are realized from the harvest. For example, marketing 1 000 fish weighing 100 g each at 8.00 (US$1) to a kilo will amount to 800 (US$100). However, if allowed to grow to 500 g each the same number (1 000) will weigh 500 kilos and at the same price of 8.00 a kilo value of sale will be 4,000.

It takes only about twice as much time to grow the fish from 100 g to 500 g but the returns that may be realized is more than four times.

Harvesting is timed when the prices of fish are at high levels which depend on the availability and abundance of fish in the market. In Metro Manila which is the principal market for the produce of fish from pens and the catch from deepsea fishing, the price of fish fluctuates very greatly. During new moon nights, big catches from the sea are landed which more often cause market glut bringing down the price of fish at their lowest levels. During full moon nights, however, not much fish are landed from deepsea fishing so that their prices are at high levels. This is the best time to harvest fish in the pens.

During stormy days and prolonged strong winds of the northeast and southwest monsoons, most fishing boats are tied at the docks so that there is scarcity of fish in the Metro Manila markets. Immediately after these strong winds have subsided and before the fishing boats could go out fishing and land their catch, the fish in the pens are harvested to take advantage of high prices.

2.2 Methods of harvesting

There are three principal gears used in harvesting the produce from the pens, namely, (1) the seine, (2) the gill net, and (3) the cast net.

2.2.1 Harvesting of fish by seining

Seining is the most common method of harvesting fish in the fishpen. The bigger seines can cover an area of about five hectares in one haul. The outfit consists of the seine net, a motorized boat used for towing the net to and from the pen to be fished and dragging the net in operation, the boat for loading the net and several small non-motorized bancas (dugouts) for the fishermen to ride on during the seining operation. From 15 to 20 fishermen are needed to operate the seining outfit.

The seine is a long rectangular net to the top of which (float line) are attached wooden or plastic floats and at the bottom line are stringed the lead sinkers. Thus, when the net is dropped in water it forms a curtain from the surface to the bottom of the lake.

The operation starts by dropping one end of the net (the fore end) and tying it securely on a bamboo pole stuck deep into the mud. The rest of the net is laid out to encircle an area. The hind end of the net is then tied to the motorized boat which pulls and drags the net reducing the enclosure little by little and finally driving the fish into the preset bag net. The bag net is then raised and the catch is collected by bailing.

2.2.2 Harvesting by gill netting

The fish in small pens are harvested with the use of gill nets. Gill nets are also used to complete the harvest of the remaining fish after seining.

The gill net outfit consists of a small dugout of about one half to one ton capacity (usually motorized) and gill nets. The gill nets are made of fine monofilament threads which can entangle easily the fish that pass through. The net with floats on top and sinkers below is spread like a curtain in water.

The gill net is divided into segments each about 50 m long. There are about from 20 to 30 segments used in harvesting the fish in pens.

In operation the segments are first joined end to end. The net is paid out from the banca that is being rowed slowly. The nets are either laid in a circle or in a straight or zigzag manner.

The net is made to stand in water for about an hour or so before it is hauled back into the boat. The fish caught are untangled as the nets are being loaded.

Harvesting by gill netting may last from five or more hours before a boat load (about one half to one ton) could be made.

2.2.3 Harvesting by cast netting

The cast net is conical in shape to the baseline of which is attached to lead sinkers that sink the net down to the bottom of the lake in a matter of seconds. To the apex of the net is tied a short rope for the operator to hold on. The length of the net is about 5 m.

In operation, the net is thrown in the water from the boat/ banca and spreads in a circular form before touching water. The apex of the net is held securely as the net sinks. As soon as it is felt the net has touched bottom, it is then pulled little by little contracting the bottom line until the lead sinkers are lumped together. At this position, the net is then hauled up to collect the fish catch.

The operation is continued until the desired amount of catch is made. It takes about five or more hours to catch a boat load of about one half ton.


Milkfish is generally marketed fresh. The fish should be carefully handled and properly treated in order to keep the quality as high as possible. It is a delicate fish which spoils very easily. Spoilage sets in after death and without treatment the fish becomes stale in less than one day.

Icing is the most common method of preserving the quality of the fish. This is applied immediately after the fish is drawn out of the water until it is finally packed for marketing.

3.1 Treatment of fish transported on land vehicles

Fish caught by seining are chilled to death in the fish carrier boat. In this way the setting of spoilage is retarded thus prolonging the freshness of the fish.

On reaching land, the fish is immediately washed of slime and blood and packed in containers. The most common containers are the galvanized iron tub, styrofoam boxes, wooden boxes and bamboo or rattan baskets.

In packing, a layer of crushed ice is first laid at the bottom of the container followed by a layer of fish, and again by a layer of ice, and then a layer of fish and finally capped by a thick layer of ice.

The proportion of fish to ice depends on how the fish was caught. For fish caught by seining and cast netting wherein the fish did not struggle very much, the proportion of fish to ice is one to four (1:4). Fish caught by gill netting struggle in trying to free themselves from entanglement and usually die before they are hauled in the boat. Spoilage must have already set in before they are iced. In packaging these fish, more ice is needed as much as one to one proportion of ice and fish is used.

3.2 Treatment of fish transported on water craft

Another way of transporting fish to the market is through the use of live-fish boats. The boats loaded with ice, stand and wait while the fish is harvested.

The harvested fish are loaded on the boat which immediately leaves for the fish landing in Manila without packaging. Much ice is added during transport in order to keep the fish in chilled condition.

On reaching the fish landing, the fish is placed in containers after being washed ready for sale.


4.1 Methods of sale and outlet

After the fish has been packed in containers at the landing place, they are ready for the market. They are either picked up by the purchasers or the producers deliver them to the purchasers.

The type of outlet includes brokers, wholesalers, wholesaler-retailer, retailers, exporters and consumers. The marketing channel is either one or a combination of the following channels of trade:

  1. producer to broker to exporter

  2. producer to broker to wholesaler-retailer to consumer

  3. producer to broker to wholesaler to retailer to consumer

  4. producer to wholesaler-retailer to retailer to consumer

  5. producer to wholesaler to retailer to consumer

  6. producer to retailer to consumer

  7. producer to consumer

4.2 The sale of fish

The fish are sold either by weight or by measure of containers. In weight measure there is more accuracy in the amount of fish being negotiated. However, the fish have to undergo a lot of handling in weighing and much time is needed before actual sale is consummated thus exposing the fish to easy spoilage.

In container measure negotiation, uniform containers are used to load the fish. Selling/purchasing of fish is done by lots. Negotiation is fast with the least time in handling the fish. There is lesser exposure of fish to spoilage.

Actual sale of fish is consummated after the price has been fixed. The price fixing is done through oral negotiation or through secret bidding.

In oral negotiation, the seller sets the price to purchasers and after some haggling the fixed price is agreed upon.

In secret negotiation or auction sale, the purchasers approach the auctioner one after the other whispering their bid prices. The winning bidder is the one who offers the highest bid.

The payments for the fish are made directly after the negotiations, but more often payments are on deferred basis usually after the fish have been sold by the purchaser.

R. D. Guerrero III


Laguna de Bay, the largest freshwater lake in Southeast Asia, has an area of approximately 90 000 hectares. It has an average depth of 2.8 m, a predominantly muddy bottom, and a single outlet to the sea (Manila Bay), the Pasig River. Some parts of the lake become slightly saline (>1 ppt) during the dry season because of seawater incursion.

The fisheries of the lake is one of the richest in the world. Fish catch from the open water is estimated to be 120 000 metric tons annually or about 1.33 tons/ha.

Fishpens were introduced by the Laguna Lake Development Authority in 1970. With the hypereutrophic condition of the lake, the fishpens stocked with milkfish have an average annual production of 4 metric tons/ha.

Several environmental problems affect fishpen production. The backflow of the heavily-polluted Pasig River and the high nutrient inflows from domestic, industrial and agricultural activities have contributed to plankton blooms, die-offs and fishkills. Damage to the fishpens by the piling up of water hyacinths during typhoons causes about 50 percent of fish losses.

This paper will discuss the impact of the fishpen industry on the lake environment and the related administrative problems.

1 Consultant, Laguna de Bay Fishpen Development Project, Los Baos, Laguna, Philippines.


No in-depth studies on the effects of fishpens on the lake ecology have been done. Therefore, the following observations made by fishpen operators and open water fishermen are cited:

2.1 Beneficial effects of fishpens

One significant effect of the fishpens has been the increase in the population of the Arius sp, a native catfish locally known as Kanduli. Prior to the introduction of the fishpens, this species was heavily exploited. The fishpens have apparently encouraged the recovery of the species by providing shelters and breeding grounds.

The build-up of snail populations (e.g. Lymnea and Amnicola) within the fishpens has also been observed. The snails are exploited by local gatherers for duck feed. Again, the sanctuary provided by the fishpens has benefitted the snails. The accumulation of fish excreta on the fishpen bottom is believed to be conducive for snail growth.

On the whole, the stocking of milkfish in pens has enhanced the fisheries of the lake in terms of quality and quantity. The loss of fish in pens destroyed by typhoons is not a total loss. The local fishermen directly benefit from such economic misfortune of fishpen operators by catching the fish that escape to the open water.

2.2 Adverse effects of fishpens

The objection against fishpens has emanated from the fishermen and snail gatherers in the lake. It is claimed by these groups that the fishpens have deprived them of what used to be their traditional fishing grounds. This problem, however, seems to be only localized in San Pedro and Muntinlupa, Rizal, two areas that have high population densities. While the conflict between fishermen and fishpen operators does exist, the solution is perhaps administrative in nature.

The LLDA is tasked with the responsibility of regulating the fishpen industry and its impact on the other industries in the lake. To effect such regulation, a “fishpen belt zone” has been demarcated by the authority. The LLDA issues permits to approved applications of prospective fishpen operators. No fishpen is allowed to be built closer than 200 meters from the shoreline of the lake to provide for navigational lanes and other activities. A maximum area of 5 ha for an individual and 50 ha for a corporation is granted.


The fishpen industry of Laguna de Bay is afflicted by two major administrative problems. These are illegal fishpens and poachers.

3.1 Illegal fishpens

Fishpens built outside the “fishpen belt” and exceeding the allowed size limit are considered illegal. The LLDA is empowered to demolish such illegal fishpens. In the enforcement of regulations, however, the LLDA has encountered difficulties. For one, the agency lacks the necessary logistics to monitor the fishpen activities in the lake. Secondly, some municipal governments have authorized the construction of fishpens in their municipal waters without coordinating with the LLDA.

3.2 The poaching problem

Rampant pilferage of fish stocked in pens by poachers is a serious problem in most fishpen districts in Laguna de Bay. Heavy losses by operators have been reported. It is even said that a crime syndicate is involved. Operators have counteracted such forces by adopting deterrent measures. The posting of night guards and frequent patrolling have added to the high operational costs of commercial fishpens.

Aida R. Librero and Elizabeth Nicolas


From the 1970's to date, fishpens had proliferated in Laguna Lake which is the biggest lake in the country. In 1973, there were 993 fishpens in the lake ranging from less than a hectare to more than 100 ha with a total area of 4 802 ha. The Laguna Lake Development Authority (LLDA), a government agency which pioneered in fishpen culture of milkfish in Laguna Lake, claims that the industry can grow to perhaps 15 000 to 20 000 ha. This would mean a lake fishery production of about 80 000 metric tons annually. The LLDA, BFAR and other concerned agencies have identified an area designated as “fishpen belt” totalling 15 580 ha. However, this growth could only be achieved if fishpen investors observe and maintain recommended practices for optimum production. Otherwise, any ecological imbalance in the lake due to mismanagement could result in massive adverse effects not only for fishpens but for the lake in general. Consequently, fishermen in the lake could be affected. Ecological, biological and socio-economic considerations need to be taken into account in decisions to expand fishpen operations.

This study aims to assess the present technology in fishpen culture, its level of productivity and profitability

In the Philippines, fishpens are operated mainly in Laguna de Bay (or Laguna Lake). Laguna de Bay lies east and generally south of Manila. Somewhat brackish, the lake has an area of 91 136 ha and an average depth of 2.8 m. The northern portion of the lake is in the province of Rizal and the southern portion in Laguna. About 80 percent of the fishpens are located in Rizal and 20 percent in Laguna.

A sample of 174 fishpen operators comprising 17.5 percent of the fishpens located in the lake were surveyed. Data presented in this study refer to the period 1974–1975. The cost and returns analysis, however, was adjusted to approximate 1980 price levels by using relevant consumer price indices for milkfish and for inputs.

1 Director and Research Associate, respectively, Socio-Economics Research Division, Philippine Council for Agriculture and Resources Research, Los Baos, Laguna, Philippines.


Fishpen owners usually reside elsewhere, hence almost three-fourths of the respondents were caretakers. On the average, an operator was male and 43 years old with owners slightly older than caretakers. He reached second year high school but was not able to finish it. Moreover, 5 percent were not able to study. It was observed that operators with higher education tended to work in other occupations in addition to fishpen operations. Owners spent almost one half of the 12-month potential time on fishpen operations and 6.4 months in other occupations such as business, fishing and farming. These occupations, earned for them an annual income of 10,049. Caretakers, on the other hand, were employed almost all throughout the year.

Fishpen as a method of fish culture in lakes was introduced in 1970, hence, the respondents were relatively new in the operation. They had only 2.6 years of experience in fishpen operation at the time of the survey.

The household of a fishpen operator was composed of about 7.2 members with only one other member being able to help in the fishpen and/or contribute to family income. This member had about 10 years of schooling and spent his time as follows: 1.7 months in the fishpen, 9.2 months in other occupations and one month not gainfully employed.


Fishpen aquaculture in Laguna de Bay was introduced in 1970 by the Laguna Lake Development Authority (LLDA) when it constructed a pen at Looc, Cardona, Rizal. During the same year three of the respondents for this study started their fishpen operations with a total area of 12 ha or about 4 ha per operator. Fishpens did not proliferate until 2 years later, in 1972, when 15 percent in Rizal and 17 percent in Laguna started cultivating fish in pens (Table 1). The greatest influx in Rizal came in 1973 and one year later for Laguna. By 1974, 55 of the sample fishpens with a total area of 415 ha were just starting their operations.

It was reported that the pen area peaked at 7 000 ha in 1974 but has declined thereafter leaving only about 2 600 ha in 1977, 2 000 ha in Rizal and 600 ha in Laguna1.

1 Fisheries of Laguna de Bay. Comprehensive Water Quality Management Program, Vol. 8, May 1978.


Milkfish was the predominant species cultured in fishpens in Laguna Lake, 96 percent cultured pure milkfish, while 2 percent had milkfish with other species like tilapia and carp. The former had an average area of 6.64 ha while the latter had 4.33 ha. Three pens cultured purely tilapia in an average area of 2.33 ha.

In 1974, an individual was allowed a maximum area of 10 ha and 50 ha for corporations, associations, partnerships or cooperatives. These maximum areas, however, could be increased or decreased by the Minister of Natural Resources for reasons of public interest such as: (1) the financial capacity and/or qualifications of the applicant; (2) the socio-economic importance of the project; (3) the existence of other applicants in the place where the area applied for is located.

Majority (61 percent) of fishpens in Laguna Lake were managed by single proprietors; 22 (17 percent) were owned by partners and corporations.

The size of fishpens varied from less than 1 ha to more than 100 ha. In a 1973 report of the LLDA, the median size of fishpens was 5–10 ha, in Laguna. Rizal fishpens were concentrated in the 10–20 and 20–50 ha brackets reflecting larger investments in fishpen per unit of ownership in Rizal. Based on the sample for this study, almost 50 percent of the pens in Laguna Lake had areas ranging from 1–5 ha. In Laguna, majority of the pen areas ranged from 1.0–30 ha or an average of 5.52 ha. In Rizal, most pens had areas ranging from 0.16–45 ha averaging 6.65 ha.

In general, the principal materials used in constructing a fishpen were bamboo and nets. They were mostly rectangular or square in shape. However, studies show that the circular/oval-shaped pen has more advantages: (a) less material and labour input in constructing the enclosure, (b) dirt, obstacles and water hyacinths carried by wind and waves do not stay in one corner but find a way out of the wells of the pens; and (c) during strong wind and rains the fish do not get trapped in the corners but swim around in schools1.

Before stocking, nurseries were temporarily constructed in a small portion of the pen area. The nursery acclimatizes the fingerlings or makes possible the rearing of fry or fingerlings to suitable sizes. It therefore affords close supervision of the fingerlings during the initial stage of their growth until such time that they are big enough for release to the entire pen. More than three-fourths of the sample pens had nurseries. The Rizal pens had a larger nursery area of 4 300 sq m and a capacity of 219 thousand pieces while the Laguna pens had 1 800 sq m and a capacity of 166 thousand pieces of fingerlings.

1 Felix, Sergio. Developments in fishpen and cage culture. BFAR.

Rearing pens were subdivided into smaller compartments mainly for more effective management and to minimize the risk of great losses. The study showed that the number of rearing compartments and area per compartment increased with total pen size. In this regard Rizal pens differed from the Laguna pens. In Rizal, the number of rearing compartments did not increase proportionately with farm size. Rather, the area per compartment was enlarged to cope up with the increase in farm area. The area of rearing compartments in Laguna did not vary much with farm size but rather the number of compartments was increased to cope up with bigger farms. Thus, the average number of compartments in Laguna was twice that in Rizal while the average compartment area in the former was less than one half that of the latter.


5.1 Idling of fishpens

After harvesting, pens are laid idle to wait for the next stocking period. The fishpen is laid idle at least one month a year so that excess food and other organic matters can be completely decomposed before stocking with new fingerlings1. Three-fourths laid their pens idle for an average period of 15 weeks mostly in November, December, January or February.

5.2 Pen preparation

This includes checking and repairing of the pen and nursery structures, cleaning and elimination of predators. Fishpens, being constantly subjected to various environmental hazards in the lake like inclement weather would naturally require periodic changes and repairs depending on the quality and durability of material used. Many of the fishpen structures were relatively new, hence, about three-fourths had not been changed. For those who did, 9 percent in Laguna Lake changed their pens every year, while the rest changed their pens after two to three years at most. Checking of pens above and below water is a daily routine although some checked every other day to weekly.

5.3 Pest/predator eradication

All the sample pens cultured either milkfish, tilapia, carp or a combination of these species. Other fish species like biya, bid-bid, carp, tilapia (locally called “tilapiang tigre”), ayugin, bulan-bulan, kanduli were considered as pests or predators.

To eliminate these undesirable fish species, they were caught and either killed or eaten. If elimination of predators is done before stocking sometimes “electric shock” was employed.

1 Felix, Sergio S. “Bangos Culture in Fishpen”. Bureau of Fisheries and Aquatic Resources, May, 1975 (mimeo).

5.4 Fertilizer use

LLDA had asserted that “there must not be any addition of any kind of chemicals or organic fertilizer or animal wastes such as chicken droppings. Such wastes can trigger or support the occurrence of algal bloom which can very seriously affect water quality and can lead directly to fish mortality”. Most pens followed except for three who used chicken droppings.

5.5 Stocking practices

Fish stocks for Laguna Lake pens were obtained predominantly (98 percent) by purchasing fingerlings from Dampalit, Malabon, Rizal. In Rizal, the average quantity of fingerlings purchased per pen was 179 000 pieces compared with 95 000 pieces in Laguna. On a per hectare basis, Rizal operators bought 25 000 pieces while Laguna purchased 16 000 pieces. About two-thirds purchased fingerlings only once a year which was usually timed when fingerlings were abundant. From the source, stocks were commonly transported in a large motorized boat locally called “pituya”. The fingerlings were directly placed in this boat which was then filled with nursery pond water, thus acclimating the fingerlings during transport. Freshwater from the lake is gradually poured into the banca to replace the pond water that goes out of an outlet. Thus, water circulation is maintained. When other means of transportation, e.g., bus and jeeps were used, fingerlings were placed in plastic bags with water and oxygen. Average mortality rate of fingerlings in transit ranged from 3.5–8.6 percent or an average of 7.3 percent, that is, 73 out of 1 000 fingerlings die on the way from the source until they are finally stocked in the pens. Mortality rate is directly related to the distance of the source.

5.6 Rearing practices

It took about six months from stocking to harvesting, hence, the number of rearing ranged only from one to two a year. Size of fish primarily determined the date of harvesting. Other factors considered were demand for stock, weather condition, and availability of natural food. Harvesting in Laguna Lake was more commonly done by seining.


6.1 Stocking pattern

6.1.1 Milkfish

Extensive stocking of bangos fingerlings was done in Laguna Lake pens from January to May. Approximately, three-fourths of the total requirement of the sample fishpens were stocked during these months. In quantity terms, stocking was heaviest in May and least in November and December. The annual stocking rate of bangos fingerlings was about 241 000 pieces per pen or 36 000 per ha. A direct relationship existed between stocking rate per pen and farm size naturally that is, the amount of stock per pen increased as the pen area increased (Table 2). On the other hand, an inverse relationship between stocking rate per ha and farm size was observed. This means that large farms are stocked less intensively than small farms.

Most fishpen operators are now stocking their pens more intensively1. This of course depends on the location of the pen or carrying capacity of the pen site. In other words, the carrying capacity of the pen site depends on the depth of water and availability of sufficient natural food.

6.1.2 Other species

Only five out of 174 fishpens studied in Laguna Lake cultured tilapia. Of these, three were cultured with tilapia alone and the other two in combination with bangos or carp. No discernible pattern of stocking seemed to exist in tilapia pens. The largest volume of fingerlings was stocked in March and April representing 43 percent of the total quantity stocked during the year. On the average, one ha was stocked with 32.2 thousand fingerlings in one year.

6.2 Yields

A fishpen in Laguna Lake yielded an average of about 26 000 kgs of milkfish or 3 798 kgs/ha (Table 3). Rizal fishpens were 70 percent more productive than Laguna pens. Compared with ordinary fishponds, yield per ha in fishpens was 6.5 times greater2. The eutrophic nature of the lake favours high production for pen culture even without supplemental feeding and fertilizer application. The Rizal side of the lake which is reportedly more abundant in natural food is even more productive than the Laguna side.

For tilapia, an average output of 4 151 kg/farm or 1 037 kg/ha was produced per year. The annual production per pen increased with farm size but at a decreasing rate. Thus, productivity per hectare decreased as the pen area increased. Highest production per hectare was obtained by pens with 1–5 ha area.

1 Felix, Sergio. Developments in fishpen and cage culture. BFAR.

2 See A.R. Librero, “Resource Productivity in Milkfish Culture in the Philippines”, in A.R. Librero and W. Collier (eds.) Economics of Aquaculture Sea Fishing and Coastal Resource Use in Asia, Proceedings of the second Biennial Meeting of the Agricultural Economics Society of Southeast Asia, 3–6 November 1977.


This section discusses first, the capital investments in the fishpens, second, the receipts derived and the costs of production, third, some measures of profit and finally, a comparison of the costs and returns and profits for different size groups. The original data in 1974 was adjusted to approximate 1980 price levels with the use of changes in milkfish prices for output and wholesale price index for inputs. Between 1974 and 1980, milkfish price per kilo increased by 83.72 percent while the wholesale price index used for inputs rose by 91.92 percent.

7.1 Capital investments

Assets in a fishpen consist of (1) the pen itself or the materials used in the construction plus the construction costs; (2) buildings which include a house/shed provided for the caretakers/workers/guard and possibly a shed for equipment; (3) transportation facilities including a motor boat or a banca plus other land transport facility used for the business; (4) nets; (5) containers like bags, basins, baskets; and (6) others including bolos, scales, rafts, etc. Six respondents reported having refrigerating facilities for their milkfish catch. On the average, the capital investment per fishpen in Laguna Lake amounted to 96 423 of which 80 percent is the value of the pen itself. Per hectare, the investment was 14 776. It should be noted that these are values of capital investment after depreciation has been accounted for, rather than values of newly-purchased assets.

7.2 Farm receipts

Cash receipts were derived almost wholly from sales of fish. Non-cash farm receipts include the value of fish consumed at home, given away as gifts or paid in-kind for services. Annual cash receipts averaged 35 471 per hectare while the non-cash receipts amounted to 307 per hectare (Table 4). Total farm receipts therefore was 35 778 per hectare. Farm receipts obtained by Rizal operators was 63 percent higher than Laguna operators. One factor which could account for this is the significantly higher yield obtained by the former (4 005 kg/ha) compared to the latter (2 353 kg/ha). A fishpen operator therefore obtained a gross cash and non-cash income of 232 944 per year.

7.3 Farm expenses

It took more than 28 000 to operate a hectare of pen in Laguna de Bay with approximately 93 percent in cash and 7 percent non-cash (Table 5). The cost of fingerlings was the primary item of expense comprising 66 percent and 48 percent of the total cost for Rizal and Laguna, respectively. It is important to stress at this point that the big difference in the cost of stock between Rizal and Laguna was due mainly to the wide discrepancy in the price paid for their fingerlings. Rizal operators paid a much higher price than Laguna operators, thus although the stocking rate were more or less the same, the total cost differed. The two other major items of expenses were the cost of labour and equipment purchased. Other cash expenses included supplementary feeds, oil, repairs, light, handling, and interests on loans. Non-cash expenses, on the other hand, included the imputed value of family labour, decrease in inventory and payments inkind for services.

On the whole, one fishpen operator spent about 183 000 per year for the whole area used for fish culture.

7.4 Net returns

Two measures were used to determine the profitability of fish culture in pens: (1) net cash farm income gives an indication of the cash return from the operations, and (2) total net farm income which includes both cash and non-cash net income. A fishpen in Laguna Lake earned a net cash income of 59 775 (Table 6). With an average rearing area of 6.5 ha, this is equivalent to 7 635 per hectare. Due to higher non-cash expenses, total net farm income amounted only to 49 704 per or 7 635 per hectare, a rate of return of 27 percent over operating expenses or 33 percent of fixed capital investment. In terms of both net cash income and total net farm, Rizal pens profited more than the Laguna pens. Income figures indicate that about 22 centavos is earned for every peso spent in Rizal while it was only 11 centavos in Laguna.

7.5 Costs and returns by farm size

By farm size, highest profit was obtained in farms with areas of 1.01– 5.0 ha (Table 7). Both the net cash income and the total net farm income were almost twice that of the average for all farms. Moreover, about 44 centavos are returned to the operator for every peso invested to operate his pen. Net returns per hectare increased with size of pen until 5 ha after which it started to decline. The least profit per hectare was obtained by large farms with area of more than 10 ha. Some caution, however, should be exercised in making conclusions based on the costs and income for different pen sizes. It is possible that in collecting data from various respondents incomes may have been underestimated by large farms.


A crucial decision that has to be made by a producer is the quantity of input that should be used in the production process in order to obtain the maximum net income subject to the resources available to him. One framework for such decision-making is the production function analysis. A production function is a relationship between input, (e.g., labour or fingerlings), and output, (e.g., kilograms of fish). This is illustrated by the Total Product curve on Fig. 1.

Total Revenue is the value of output obtained by multiplying the price of the output by the volume of output. If the producer is small enough that he cannot influence the price of output, then the shape of the total revenue function is the same as that of the total product curve.

To determine the optimum level of input, that is, one that will yield maximum profits (given the level of other inputs used) the condition is that the value of marginal product must be equal to the price of the input1 The marginal product (MP) is the quantity of additional output generated by an additional unit of input. Multiplying MP by the price of the output gives the value of marginal product (VMP). Thus, the VMP represents the amount by which total revenue changes when an additional unit of input is added. In other words, the VMP is the additional income derived for every additional unit of input. On the other hand, the price of the input is the additional cost of each unit of input. The maximum profit therefore is that point where the additional income is just equal to the additional cost. This is represented by point A in Fig. 1. Applying a level of input less than 4.8 units means that the amount of income the producer could get is greater than the amount he has to spend. But if he operates beyond this point, he will be spending more money than what he could expect to receive.

1 Only the basic concepts are presented in this paper. There are other conditions and assumptions which cannot be discussed here. The trainees are referred to basic textbooks in microeconomic theory.

Applying this analysis to the fishpen data1, the production function was estimated using the quantity of fish produced per year as output and the following as inputs: fishpen area, fingerling expense, labour expense, and other operating costs. The analysis showed that fishpen operations have not yet reached the optimum level, that is, the value of marginal product is greater than the price of the various production factors used. This implies that income could still be raised by increasing the levels of the said inputs.

1 Ramirez, Jimmy. Productivity and returns to inputs of fishpen aquaculture in the Philippines. Unpublished M.S. Thesis, U.P. at Los Baos, College, Laguna. 1978.


One of the limiting factors in fishpen aquaculture is the substantial initial capital investment. One measure of the earning efficiency of investment is through benefit-cost analysis. The present value of the stream of annual benefits and cost is compared over the economic life span of the investment. The present analysis is based on the assumption that the period covered by the survey is normal, the output of the investment remains constant throughout the economic life of the fishpen, which is considered to be 3 years, and a 12 percent per annum discount rate as the opportunity cost of capital.

Table 8 shows the summary of the benefit-cost analysis done on the sample fishpens. The Net Present Worth (NPW) was computed by subtracting the stream of present value of costs from the stream of present value of benefits. Due to a higher initial investment in the base year, fishpen operations showed a negative Net Present Value implying that benefits are not enough to recover all costs at the initial year of the investment. However, over a 3-year period an average fishpen culturing milkfish had an NPW of 32 744.

The Benefit-Cost Ratio (BCR) between the two locations did not differ significantly. Both Laguna and Rizal fishpens had BCR greater than unity, averaging 1.07. The criterion set for viability of a project is a BCR equal or greater than unity. Hence, the fishpen business in Laguna Lake was considered profitable. The internal rate return (IRR) was another criterion in judging profitability. The criterion is to select the project whose IRR is greater than the opportunity cost of capital assumed in this study as 12 percent. The desired IRR is reached by applying a series of discount rates to the stream of benefits and costs until the benefits and costs equal or the NPW is zero. The average IRR was estimated to be around 35 percent.

A benefit-cost analysis was done for small pens (less than 5 ha) and large pens (5 ha or bigger). The test showed that investing in small or large pens were both viable with small pens having a BCR of 1.10 and large pens, 1.05. The magnitude of the internal rate of return, 35 percent, was the same for both groups.

Previous Page Top of Page Next Page