by
Pedro G. Padlan1
FAO Aquaculturist
Pilot Project for Intensified Aquaculture Production
El Zawya, Kafr El Sheikh Dir., Egypt
Inter-tidal zones are coastal areas which are under water during high tides and exposed during low tides. They comprise the beaches, mud flats and swamps, often-times supporting stands of various species of halophytic plants. The extent of these belts may be from a few meters wide to stretches reaching many kilometers inland.
By tidal energy, sea water is pushed inland either directly over the land mass itself or through creeks, estuaries and rivers where mixing with fresh water from the interior regions dilutes it to brackishwater condition.
Nowhere in the world have such vast portions of these areas been converted into fishponds as in the Far East. As of 1976, four countries - Indonesia, the Philippines, China (Taiwan) and Thailand - had close to 400 000 ha of brackishwater ponds producing some 185 000 metric tons of fish and shellfish and contributing from 4 percent to 8 percent of their total fish production (SEAFDEC, 1978).
Milkfish (Chanos chanos) and shrimps (Penaeidae) make up the major part of the yield using both mono- and polyculture methods. Mullets, tilapia (T. mossambica), crabs (Scylla serrata) and other finfishes which come in with the water during their early stages of growth are the miscellaneous components of the harvest. In some cases, crabs are intentionally added. The females with developed gonads command high market prices.
Yields of over two tons of milkfish and from 250 to 800 kg of shrimps per hectare per year without supplemental feeding have been attained in traditional ponds. These potentials, the increasing demand for cheap protein and a fair rate of internal return from well managed farms have provoked interests in the utilization of coastal land, with the centuries-old fish farming industry being reborn where resources are present.
Economy in construction, low risk factor and ease in management and supervision are the major considerations in the selection of site. On these bases, many criteria have been advanced, the most important being briefly described hereunder.
These two factors determine water adequacy with tidal energy being the free and main force for filling and draining, utilized with almost precise predictability. A tidal range of between 2–3 m is the most desirable (Jamandre and Rabanal, 1975). Complimentary to the range of tide, land elevation remains the key as to whether there will be ample time for watering or dewatering and whether there will be problems of lack or excess of soil materials for diking and other purposes.
For milkfish farming, experience and observations have shown that the best elevation is one where from 0.2 m of sea water to 1 m of fairly low salinity waters (10–20 ppt) which may be brought in by freshets during the rainy season could be easily maintained, yet readily drained any day or for most part of the year (Padlan, 1977). Shrimps require a minimum of about 0.4 m as long as wide internal canals are provided (Cook, 1976). Depths up to 1 m are considered optimum.
Clay loam soils make strong, water retentive dikes and impermeable bottoms. They are also highly responsive to fertilization and get quickly stabilized. Studies in Taiwan have shown that loam soils produce the highest weight of benthic algae (Tang and Chen, 1967).
Acid sulfate soils are most often encountered where there are excessive roots of Rhizophora. It takes years to improve such type of soil, often necessitating constant flushing, leaching and treatment with lime and fertilizers to neutralize the upper layer and encourage the formation of a favourable substrate. An estimate of the acid potential can be obtained by incubating moist soil 1 cm thick in a thin plastic bag and testing for pH after 30 days. A pH lower than 4 indicates high acid reserves (Camacho, 1977).
Level areas are most ideal but these are quite rare to find except in small young deltas. More often, the terrain is irregular, occasionally dotted by mounds of the crustacean Thallasina scorpionoides and traversed by tidal creeks. Pond layout is frequently dictated by the topography of the land. Prospective pond owners, in making their development plan, fit the elevation requirements of the different ponds to the areas which match them in order to minimize leveling expenses.
Various kinds of mangroves can grow into big trees which form canopies over tropical swamps. Species of Rhizophora, Sonneratia and Avicenia may form thick stands in low areas while Xylocarpus, Heritiera, Bruguiera, etc. may dominate the middle higher areas. Trees do not have much value inside ponds and consequently have to be removed. Those more than 30 cm in diameter are difficult and expensive to cut and uproot.
Big waves generated by heavy winds during storms almost always cause breaks in the dikes fronting the sea. Similarly, resulting floods of long duration weaken levees, eventually breaching them. The accompanying heavy rains alone can drastically change salinity in shallow ponds within a short time and cause deterioration of natural food conditions which had been previously established and maintained. Land areas inside typhoon belts should be avoided as much as possible.
The brackishwater ponds of the Far East were constructed mainly by manual labour. Experienced workers who could toil waist deep in water on dike construction jobs have appeared in localities where the industry has become established. In newly developed areas, they may be difficult to find. Local hands could be trained but considering that working time is limited by tidal conditions, construction could suffer delays and could become very expensive if not completed while circumstances are favourable. The seasonal demands of other industries in the locality will also have to be weighed carefully. Imported skilled labourers generally press for higher wages and create logistic problems.
Lately, hydraulic cranes and back-hoes mounted on barges have proved versatile and much cheaper to operate in the long run provided the equipment is well maintained. Swamp dozers are also being used for interior earthworks once the ponds are enclosed and can be thoroughly dried.
Further considerations have to be taken on such matters as pollution sources and availability of supplies and materials needed for construction and operations, roads, navigable waterways, ice plants, markets, etc. The ease with which such inputs could be acquired and brought to the pond site as well as the marketing of the fish product should make management easier and more profitable.
Well planned conventional farms for milkfish culture almost always consist of nursery ponds, holding ponds, production ponds and common water supply and drain canals (Fig. 1). Recent addition to the nursery ponds in the Philippines are small acclimation tanks built as in Taiwan.
The nursery ponds range from 5 to 50 ares.1 They are also the shallowest and most elevated ponds, being consequently situated as close to the water source as possible unless otherwise called for.
Holding ponds are larger areas where the fingerlings from the nursery ponds are transformed for further rearing. Actually they function as reservoirs from which the production ponds draw their stock. When not in use, marketable fish are held here for a few days while waiting for marketing conditions to improve.
Production ponds range from 1 to 20 ha or more. It is not uncommon to see big units of up to 100 ha in farms where operations are on an extensive scale.
Catching ponds are sometimes incorporated in the layout. These are small compartments where the fish can be herded and easily harvested.
Water supply canals facilitate filling or draining of ponds independently of each other. They could also confine fish for short periods. In Taiwan a more extensive canal system is maintained for acclimatizing the stock before they are transferred into the more saline production ponds. Extra wide deep canals, called wintering ponds, are also provided to over-winter the yearlings (Fig. 2).
Sluices control water intake and drainage. They have single or multiple openings, being constructed of wood, masonry or concrete and fitted with wooden flush boards and screens.
Quite lately, the progressive type layout (Fig. 3) has become popular in the Philippines. It consists of a series of successively larger ponds where the fish are shifted at regular intervals until they reach the biggest pond where they attain marketable size. The area ratio of the production ponds is usually 1:2:3 or 1:2:4.
1 1 are = 100 sq.meters = 0.01 ha
The traditional milkfish ponds of the Philippines and Indonesia are also utilized for polyculture of shrimps and milkfish. In Thailand, however, fish farmers have come up with a design for rearing shrimps alone. The layout (Fig. 4) consists of two or three production ponds abutting a common head pond which serves as the nursery pond. A drain canal can empty the production ponds during low tide. Philippine fish farmers, particularly in sectors where private small scale shrimp hatcheries are being set up, envisage layouts similar to the sketch shown in Fig. 5.
An improved layout for monoculture of shrimps with daily partial water exchange and intensive feeding is now widely used in Taiwan. Among its important features are facilities to control salinity. Sea water is piped in and mixed with ground water to reduce salinity to 8–20 ppt, the range considered best for the grass shrimp, P. monodon.
Figure 1: Layouts of conventional milkfish farms in the Philippines.
A : simple layout for areas up to 10 ha
B : layout with long water supply canal (areas 20–40 ha)
C : layout with short water supply canal (areas 20–40 ha)
| Legend: | |||
 | — | - | Dike |
| • | - | Sluice | |
| □ | - | Acclimation tank | |
| CP | - | Catching pond | |
| NP | - | Nursery pond | |
| HP | - | Holding pond | |
| PP | - | Production pond | |
| WSC | - | Water supply canal | |
 | - | Catch pond for nurseries | |
 |  |
Figure 2: Schematic layout of a milkfish farm in Taiwan (Lin, 1966), with secondary canals (SC), wintering ponds (WP) and acclimatization tanks (a).
Figure 3: Layout of a progressive type milkfish farm in the Philippines (Denila, 1977).
Figure 4: Layout for a shrimp farm using a monocultural system in Thailand (Cook, 1976).
Figure 5: Layout for a shrimp farm as proposed in the Philippines (Santos, 1978).
Construction work is generally timed to start when the higher high tides occur at night thereby allowing the workers to have longer working hours when water levels are low during the day. This period is from September through March in the Far Eastern region.
The perimeter dike is first laid. To provide strong bonding with the ground and to eliminate future leaks, all trees along its path are cleared, big roots extracted and a puddle trench dug in the centre along the entire length. Where the dike will traverse creeks the latter are first dammed and the dike raised sufficiently to avoid washout of the new fill when tide waters rise or recede.
Dikes are constructed with soil cubes cut out with flat blades and piled layer by layer until the desired dimensions are reached. The various manners of dike construction are roughly illustrated in Figures 6 and 7.
The main sluice is set in place while perimeter dike construction is going on. By the time the dike is completed, water level can be regulated for more efficient performance of the workers. General development and improvement ensue.
Milkfish ponds require flat bottoms with a slight declination towards the sluices. Shrimp ponds, on the other hand, may not be levelled provided the interior canals can easily be drained. Pond soils should be throughly worked over up to a depth of 15 to 20 cm to hasten oxidation processes.
Cranes and back-hoes mounted on barges are brought to the site. Since they need water to be operational, construction activities start when tide conditions are high during the day. Working from within they excavate soil material for the main levee forming canals as they move along. The canals serve as channels for floating the equipment.
Uprooting trees is easily accomplished with motor or hand powered winches and capstans using stout cables. But for the big ones it may be necessary to detach the main roots partially from the soil before their removal. The use of high pressure pumps for this purpose has been found quite effective. Small stumps can be pulled out with a small winch conveniently mounted on a flatboat.
Swamp dozers are getting popular and are now being utilized where the ground can be sufficiently hardened to hold them. Work time, however, is limited to the dry season.
The farming of milkfish in brackishwater ponds of Indonesia, Taiwan and the Philippines has been described in great detail by various authors (Chen, 1976; Lin, 1966; Rabanal, 1974; and Schuster, 1952). It consists basically in shallow water fish culture with depths seldom exceeding 40 cm to keep the benthic algal pastures flourishing. Lately it has been observed that raising this level gradually to about 1 m with low salinity water and maintaining a dense bloom of phytoplankton (Anabaena, Scenedesmus, Microcystis, etc.) by regular use of chemical fertilizers or a combination of both inorganic and organic fertilizers, very high yields can be produced also.
In the integrated system, one starts with the stocking of the nursery ponds with fry, growing them to post-fingerling size through the holding ponds and rearing them to marketable size in the production ponds.
Figure 6: Dike construction for intertidal ponds by manual labour (Denila, 1978).
Figure 7: Tips on dike construction by manual labour (Denila, 1978)
The fry are caught wild along the beaches. A conglomeration of fishing equipment are used to collect them. Very common in the Philippines aside from seines and push nets are traps consisting of two wings forming a V at the convergence of which a fine mesh bag is attached. These traps are set facing the sea to catch the fry that are brought towards the shore by the incoming tide. The wings are of flattened whole length bamboos. In Indonesia lures made of dry banana leaf strips secured to long lines are hung in the fry grounds. A triangular fine mesh hand net is passed under the lures to catch the fry. In Taiwan motorized boats tow nets up to 1 km from the shore to augment whatever catches there are from the beach. The fry seasons are April – July and September – November in Indonesia and the Philippines. In Taiwan it starts in spring and lasts until August.
Stocking of the nursery ponds is done at one time after adequate microbenthic algae (predominantly diatoms and blue-greens) have been cultured. The fry are carefully acclimatized in a tank before they are released to the more saline water of the nursery ponds. Normal stocking rates vary from 20 to 50 fry/sq.m.
The fish stay for a maximum of 30 days in the nursery ponds after which they are shifted to the holding ponds. If there was a previous lack of stocking material the early fingerlings are directly transferred to the production ponds.
Production ponds are stocked with uniform size fingerlings or with multi-size groups at quantities reaching up to 6 000/ha at one time. At appropriate periods thinning is done. Additional fingerlings are introduced after each partial harvest if food is still sufficient. Otherwise the remaining fish are totally harvested after the food runs out.
The progressive system requires periodical transfer of the stock to the next larger pond in the series until they reach the biggest pond where they attain marketable size. A regular schedule of pond preparation, stocking and cropping with 4–6 weeks of rearing in each pond makes from four to six harvests in a year possible.
The natural food more preferred by milkfish in ponds are the benthic algae developed on the bottom by a technique involving the right amount of drying, adequate fertilization with organic and inorganic fertilizers and controlled water flow. Rice bran, peanut and soybean cakes are supplementary feeds commonly given to the fish during the later part of the rearing season.
Fortunately milkfish are almost entirely free of diseases. Pests, however, are more serious problems in the ponds. Snails (Cerithidae) and chironomid larvae compete heavily with milkfish for food. In Indonesia triphenyltin acetate is still used to control snails. Organophosphate pesticides, particularly Diazinon, Abate and Sumithion are effective against chironomid larvae but they are very specific to shrimps.
The fish are harvested by utilizing their natural instinct to go against the current, drawing them into the supply canal or catching pond where they are seined with little effort. In Taiwan selective gill nets are dragged all over the pond.
Shrimp culture is very often done in association with milkfish rearing. The substantial income derived from this highly priced commodity has encouraged many fish farmers to strive for greater productions, some even willing to relegate milkfish to the background when conditions were optimum (ASEAN, 1978).
Six shrimp are most common: Penaeus monodon (grass shrimp), P. merguiensis (banana shrimp), P. indicus (white shrimp), Metapenaeus ensis and M. monoceros (sand shrimps) and M. brevicornis (yellow shrimp).
The fry come in with tide waters as the ponds are being filled. But ingenious methods of intensifying natural recruitment have been devised by fish farmers. In Thailand propeller and dragon wheel pumps (Figs. 8 and 9) bring water with the fry to the raised nursery pond (Jamandre, 1977 and Schuster, 1952). In the Philippines branches are staked near the main sluice to attract the fry to periphyton that eventually develop on them. Some ponds have wide low gates where much water can overflow during high tides. As the tide recedes and the excess water drains back many fry remain behind.
Of the six species mentioned above grass shrimps and sand shrimps are considered the most important, the former because they are the fastest growing, reaching 30–60 g in 4–6 months. Sand shrimps attain marketable size of 5–10 g in 60–90 days. More interest has been shown by fish farmers for these two species. Where natural fry grounds are known, collectors gather the post larvae for stocking purposes.
The fry of P. monodon are caught with milkfish fry along the shore. In tidal creeks and estuaries well developed post larvae are found clinging to twigs. Catchers use this characteristic to advantage by setting dead branches or wreaths of long creeping grasses along the banks. At regular intervals hand nets are slipped under these lures and the fry collected.
Pond owners shifting to P. monodon as the major crop, stock their ponds with the shrimp fry one to two months ahead of milkfish. On the other hand sand shrimp juveniles bought from shrimp fishermen using push nets are released any time during the milkfish growing season provided that at least 2 months are available to grow to marketable size.
In such polyculture system the shrimps are grown without much care except to ensure that the gates are provided with fine screens to prevent entry of predators during water exchanges. Occasionally entrails and skins of freshly slaughtered animals are tossed into the pond to provide additional food for P. monodon.
Fish farmers have observed that in ponds containing moderate growths of filamentous green algae (Chaetomorpha sp. and Cladophora sp.) higher yields have been obtained from natural recruitment. This could perhaps be due to the fact that as algae develop they attract more animal organisms which the shrimps can readily use as food. In fertilized ponds, periphyton attached to the algal filaments could be twice as thick as the filaments themselves.
The monoculture of shrimps in Taiwan may not be readily adaptable in developing countries but in Thailand, shrimp farmers have developed their own technology of raising shrimps alone. After pumping water into the nursery pond for 30 days, tea seed cake is applied at the rate of 10–25 g/cu.m. of pond water to kill all fish.1 The water is then drawn by gravity to the adjacent production pond where the shrimps are reared for 1–2 months. With two or three production ponds served by one common nursery pond, a 60–90 day rearing cycle can be conveniently attained.
There are isolated reports of diseases of shrimps in the above-described culture systems. Black gills are suspected to be due to bacteria, fungus or detritus. Slow growth and soft exoskeleton of P. monodon have often been observed and may be due to nutritional deficiencies and poor pond conditions. New diseases are being discovered but are confined mostly where intensive monoculture is practiced.
Various methods are used to catch shrimps from the ponds. During dark nights, partial drainage of the surface waters where the shrimps have come up starting at nightfall draws them to a bag net fitted at the end of the sluice or to a trap, made of bamboo screens set in the water supply canal. Inside the pond, a trap, also of bamboo screens can be set up. A short leader, set perpendicularly from the dike leads the swimming shrimps into the trap (Fig. 10). Portable traps which can be quickly installed along the same principle are used in Indonesia. The remaining shrimps are harvested when the ponds are totally drained.
Figure 8: Propeller pump for shrimp ponds in Thailand (Jamandre, 1977)
Figure9 : Dragon-wheel pumps run either by engine or by wind power (Tamyavanich, 1977).
Fig. 10 - Shrimp trap inside pond
Female crabs (Scylla serrata) are monocultured in small ponds in Taiwan where they are stocked after copulation and reared until they attain full gonadal development. The ponds are about 350 sq.m. Big ponds are divided into four small ponds and provided with a small rectangular water inlet at the centre where the partition dikes intersect. The crabs, with carapace width of 7–12 cm are held in separate batches in different ponds at the density of 3/sq.m. They are harvested 20–50 days after stocking. They are fed with soft-shelled snails of the fresh water species, trash fish and animal food. Snails are the most efficient feed for maturation purposes.
In polyculture with milkfish, young crabs of both sexes are stocked. Stocking rates are variable, mainly depending on the catch of the fishermen. Maximum stocking rate in Taiwan is 10 000/ha.
Escape is prevented by fencing the pond with bamboo lattice set at an angle all along the entire perimeter dike. Scylla, however, bore holes through the dike and get out of the pond in this manner. It is for this reason that many fish farmers are not too enthusiastic about raising crabs in their ponds.
Crabs are easily caught when they congregate at the sluice as new water is let in. Inside the ponds, they are captured with crab pots baited with fresh fish or meat. They can also be gathered with small 50-cm square lift nets, above which baits are hung from the cross frame. As many lift nets as can be baited are set in the pond and pulled out from time to time.
The crabs have to be tied individually and their pinchers immobilized. During transport they are wetted with clean sea or brackishwater quite frequently. Under these conditions they remain alive for as long as five days.
Coastal pondfish culture presents certain risks to small investors in particular. Many such hopeful investors have lost their life-time savings in this venture where ample reserves and perseverance are required. For example, it takes at least two years for the soil to stabilize after full development and during this period it might even be difficult to cover operating costs.
Many governments are now recognizing the significant contribution of aquaculture to the national economy. They have initiated, even liberalized, lending policies to assist prospective and actual fishpond operators.
The Development Bank of the Philippines, a government banking corporation, gives loans to the extent needed by the fish farmer provided that (a) he has started development work, (b) he has the required equity or counterpart fund and (c) he has a realistic project study and programme of development acceptable to the Bank. The fish farm itself, whether privately owned or leased from the Government, is the collateral. In the latter case, a 25-year lease agreement between Government and leasee and an assignment of rights to the Bank by the lessor are the main requisites.
Indonesia has a government bank catering for the needs of small-scale fish farmers, individual holdings in the province of South Sulawesi and the island of Java for example varying from 1.5 to 3.5 ha. Its financing programme provides loans, about 90% of which goes to land acquisition and development, and the rest to operation cost. Working capital credit is also given for rehabilitation/improvement of ponds as well as for procurement of supplies and materials, insured by a government credit insurance corporation. The ponds are collaterals for the loan (Sidarto, 1977).
Despite such financial assistances, inflationary trends tend to act negatively against the lending schemes particularly where there is considerable delay between application for and release of the loan money.
Technological developments in aquaculture have progressed quite fast during the last few decades, yet there are very few aquaculturists and qualified technicians who could attend to the manpower needs of the sector.
Secondary fishery schools have turned out scores of technicians in Indonesia and the Philippines. Universities and colleges have also produced aquaculturists with Bachelors' and Masters' degrees. Most of the graduates have been absorbed by the government and assigned to demonstration fish farms and the extension service. But there does not seem to be enough of them to work at the grass root level, close of the farmers.
Short training courses for farmers themselves, closer contacts between extension agents and fish farmers, and organizing the pond operators into active groups/associations could promote much faster dissemination of technical information and relieve to a certain extent the problem of manpower shortage.
One of the frequent drawbacks in intensive culture methods is the lack of stocking material. Indonesia and the Philippines now feel the need for more milkfish fry. This has been a perennial problem in Taiwan. The scarcity of gravid P. monodon females from the sea has also restricted operations of shrimp hatcheries in the region.
Future hopes are placed in the current researches on the artificial breeding of milkfish from controlled parent stock and on the maturation of shrimps in ponds. Studies along these lines are being conducted in the Far East at the Southeast Asian Fisheries Development Centre in Iloilo (Philippines), at the Marine Laboratory in Tungkang (China, Taiwan) and at the FAO/UNDP Shrimp and Milkfish Culture Applied Research Centre in Jepara (Indonesia).
Fish farmers have come to realize the importance of fertilizers in aquaculture. While the sources of organic fertilizers are varied, the supply is limited, often tied down to agriculture and other animal production. The cost of inorganic fertilizers, on the other hand, has risen by leaps and bounds during the last decade.
A good solution could be to convert waste plant materials into artificial manures by composting. The utilization of slaughterhouse refuse, sewage sludge, even night soil could be considered. Inorganic nitrogenous fertilizers will remain on the critical list.
ASEAN, 1978 Manual on pond culture of penaeid shrimp. Manila, Philippines, ASEAN National Coordinating Agency of the Philippines, ASEAN 77/SHR/CUL:132 p.
Camacho, A.S., 1977 Implication of acid sulfate soils in tropical fish culture. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/77/GEN/15: 97–102
Chen, T.P., 1976 Aquaculture practices in Taiwan. Farnham, Surrey, Fishing News Books Ltd., 162 p.
Cook, H.L., 1976 Problems in shrimp culture in the South China Sea region. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/76/WP/40:50 p.
Denila, L., 1977 Layout, design, construction and leveling of fishponds. In Readings on aquaculture practices. Iloilo, Philippines, SEAFDEC Aquaculture Department, vol.1:74–86
Denila, L., 1978 Improved methods of manual construction of brackishwater fishponds in the Philippines. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/GEN/77/15:233–59
Jamandre, T.G., 1978 Pumps for brackishwater aquaculture. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/76/GEN/15:393–422
Jamandre, T.G. and H.R. Rabanal, 1978 Engineering aspects of brackishwater aquaculture in the South China Sea region. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/75/WP/16
Li, Y. and I.C. Liao, 1979 Introduction to aquaculture in Taiwan. Proc.Annu.Meet.World Maricult. Soc., 10:229–51
Lin, S.Y., 1966 Milkfish farming in Taiwan - a review of practices and problems. Fish Cult.Rep. Taiwan Fish.Res.Inst., (3):63 p.
Padlan, P.G., 1977 Pond engineering. 1. Selection of site for brackishwater milkfish ponds. Iloilo, Philippines, Aquaculture Department, Southeast Asian Fisheries Development Centre, 15 p. (mimeo)
Rabanal, H.R., 1974 Technological innovation in characteristics, design and management of ponds used in brackishwater aquaculture. Paper presented to the Workshop on artisanal fisheries development in Indonesia, March 4–7, 1974. (mimeo)
Santos, C., 1978 Modern aquaculture for the Philippines. Iloilo City, Philippines, Yuhum Press, 224 p.
Schuster, W.H., 1952 Fish culture in brackishwater ponds of Java. Spec.Publ. IPFC, (1):140 p.
SEAFDEC, 1978 Fishery statistical bulletin for the South China Sea area, 1976. Thailand, Southeast Asian Fisheries Development Centre, October 1978
Sidarto, A.A., 1977 The financing of small-scale aquaculture projects, the case of brackishwater pond culture in Indonesia. In First ASEAN meeting of experts on aquaculture. Technical report. Semarang, Indonesia, 31 January to 6 February 1977, edited by H. Rabanal and H. Cook. Manila, South China Sea Fisheries Development and Coordinating Programme, ASEAN 77/FA.EgA/Rpt.2:175–85
Tamyavanich, S., 1977 Water pumps and their uses for aquaculture in Thailand. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/77/GEN/15:423–5
Tang, Y.A. and S.H. Chen, 1967 A survey of the algal pasture soils of milkfish ponds in Taiwan. FAO Fish.Rep., (44) vol.3:198–209
by
Medina N. Delmendo1
Regional Aquaculture Officer
FAO Regional Office, Bangkok, Thailand
1 Presently: FAO Fishery Coordinator, Hanoi, Viet Nam
Laguna de Bay is 900 km2 of water surface area with an average depth of 2–8 m at mean low lake level. It is hypereutrophic during the summer period due to high water temperatures (reaching up to 32°C) and nutrient inflow. During the dry season (December–May) the lake water level generally goes down to the elevation of mean sea level (MSL) in Manila Bay, resulting in the influx of sea water during the diurnal high tide periods. Consequently, salinity concentrations of 3–5 ppt occur. Saltwater intrusions due to backflows through the Pasig River, its only outlet to the sea, affects as much as one third of the lake volume. This backflow also carries with it pollutants from the Pasig River and its tributary, the Marikina River, which accounts for 21 percent of the total lake nutrient inflow. In the wet season, the lake water level rises from 1–3 m above MSL resulting in the decrease of salinity content of the water to 100–200 ppm (Delmendo and Gedney, 1976).
The mineral content of the lake fluctuates widely. This is very high at the peak of backflows, diminishing gradually after because the tributary rivers are generally low in minerals. The nitrogen input in 1973 (excluding backflows) was about 4 000 t as against 930 t of phosphorus (Final Report, Water Quality Management Programme, Vol. 4, May 1978).
The lake receives water from an extensive watershed area. The mean annual inflow including rainfall is 4 billion m3/year which is sufficient, theoretically, to flush the entire lake. About 1 billion m3/year is lost by evaporation.
The lake is located at the lower end of Luzon Island, bounded on the north by the Rizal province and on the south by the Laguna province (Fig. 1). There are 30 municipalities bordering the lake which comprise the two provinces (Rabanal, Acosta and Delmendo, 1964). The total population was approximately 5 million in 1970. At a growth rate of 2.1 percent annually, this population reaches now about 6 million.
For centuries, the lake has had a rich open water fishery. It has been the source of livelihood of many people around the lake, thus constitutes a significant sector in the economy of the lake region. It is a source of fish for human food. Catfishes, white gobies, perch and murrels are the economically desirable species which used to be available in good sizes. However, the quality of fish harvests greatly declined in the advent of motorized fishing boats beginning in the 1950s which replaced sailboats. The use of fine-meshed nets became rampant.
A fishery survey conducted in Laguna de Bay (Shimura and Delmendo, 1968, unpubl. report)1 revealed that there were 3 305 motorized fishing boats and 3 850 non-motorized outfits. There were 7 818 fishing families, the number of full-time fishermen being 7 674 and part-time fishermen 2 139. Fishing gears used included fish trap (corral), snail dredge, motorized push net, manual push net, gillnet, long line, drive-in net, and various seines. The sizes of fish caught were very small, particularly the perch and gobies.
The 1968 survey compared to the 1963 survey showed an increase in the number of full-time fishermen by 1 000 and a decrease in part-time fishermen by 4 000, which was apparently a result of fish specialization during the period. This meant that the total number of fishermen decreased from 13 000 in 1963 to 10 000 in 1968. On the other hand, the number of motorized fishing boats increased by 750 units while the non-motorized boats decreased by about the same number, therefore, the number of fishing boats remained the same in five years (Shimura and Delmendo, 1968 unpubl. report)1.
FIG. 1 - LAGUNA LAKE DEVELOPMENT AUTHORITY REGION
The estimated annual total catch of fish, shrimps and snails in 1963 and 1968 were as follows (t)1:
| Fish | Shrimps | Snails | |
| 1961–63 (annual average) | 82 882 | 19 096 | 247 770 |
| 1968 | 39 055 | 27 552 | 96 683 |
Fish catches decreased by more than 50%; shrimps increased by 44% and snails decreased by 60%. This high decrease in snail production may be due to sampling errors. Nevertheless, the 1968 snail catch is still considerably lower than the 1963 survey. There was a decrease by 27% in the number of snail dredge also. There is no open water fishery catch data available after 1968.
The shrimps and snails are mainly used for duck feeds. Duck farming is a flourishing industry around the lake. It is undertaken as a subsidiary income activity of most households along the lake which consisted of a total of 3 796 duck farms. This number is 12% less than the number of duck farms reported in the 1963 survey. Although this was so, it was, however, found that the number of ducks kept per farm increased. The total population of ducks kept was 734 000 which was 18% more than the previous survey.
From the above information it was evident that the lake fish output was decreasing and that the main catches were being utilized for animal feeds more than as human food.
Recognizing this situation, a programme of stocking the lake with milkfish (Chanos chanos) fingerlings was launched by the Bureau of Fisheries in the 1960s. But the fingerlings released into the lake did not have much chance to grow to marketable size as the fishing intensity was too high and fishing gears used were of fine-meshed nets. The programme did not have an impact on the socio-economic conditions of the fishermen for which it was carried out. Besides, the quantity of fish seeds which could be released at any one time was very small and insignificant in relation to the total area of the lake. Milkfish do not spawn in freshwater, hence, there is no possibility of reproduction in the lake.
Implementation of fishery rules and regulations controlling the net mesh sizes of fishing gears, and the declaration of open and close seasons for fishing of certain species (catfish and gobies) did not work despite intensive patrols of fish wardens on the lake. The social and economic factors involved were too strong to fully apply fishing rules and regulations to protect the lake fishery production from further decline. Fishermen apprehended for violating the fishery rules and regulations complained of lack of other sources of income. The social and economic considerations, therefore, took precedence over compliance with fisheries laws. Municipal courts were not able to penalize violators in most cases.
In May 1966, the Congress of the Philippines approved House Bill No. 5088 known as Republic Act 4850, creating the Laguna Lake Development Authority, a semi-government regional development body. It had an authorized capital of P.Ps. 100 million. The provincial governments of Rizal and Laguna owns 60 percent of the common shares of stocks.
Fig. 2 - THE LLDA PILOT FISH PEN AT LOOC, CARDONA-RIZAL, PHILIPPINES.
The LLDA's regional responsibility encompasses the Greater Manila area which includes the provinces of Rizal and Laguna (Fig. 1).
One of the main purposes of the Authority is to “undertake a comprehensive survey of the physical and natural resources, the potentials of the region; more specifically, the development of the Laguna Lake resources including its social conditions, hydrological studies, power potentials, development of scenic and tourist spots, conservation of water resources and such other regional problems and, on the basis thereof, to draft a comprehensive and detailed plan designed to promote the region's rapid social and economic development and to implement such plan” (Chap. II, Sec. 4, Rep. Act 4850 as amended by Presidential Decree 813, 1975).
On the basis of the mandate given to it by the Government of the Philippines, feasibility studies of the Laguna de Bay for domestic water supply of the greater Manila area and other uses were carried out. This is a major long-range development plan on which assistance from the United Nations Development Programme was obtained. A list of studies conducted on Laguna de Bay is shown in Appendix 1.
The main fields of activity of the LLDA are flood control, irrigated agriculture development, farmer eduction, industrial development, fishery development, pollution control and water resources development.
As detailed studies on water resources and agro-industrial developments were underway and detailed planning of the infrastructures were being made, a short-range programme on fisheries development was developed in order to improve the lot of fishermen on the lake. A pilot project to demonstrate aquaculture in enclosures (fish pen) was established.
Earlier studies on Laguna de Bay had shown that the lake was very rich in food organisms, particularly algae. This observation was further confirmed by the investigation on water quality of the lake wherein it was found that the primary production of Laguna de Bay was equivalent to 33–90 g/m2/day in terms of wet weight.
Delmendo (1966) found that the phytoplankton components of the food chain in the lake were not being fully utilized by the indigenous species. The major fish species, composed of the silver perch (Therapon plumbeus), white gobies (Glossagobius giurus) and the catfishes (Arius spp.), feed on zooplankton, shrimps and small fishes as major source of nutrition.
A comprehensive study of the economic potentials of Laguna de Bay was undertaken in 1968–70 with assistance from the United Nations Development Programme. The fishery aspect of that study focused on methods of utilizing the natural aquatic biota of the lake to obtain a higher fishery production of a higher value fish than was commonly found in the lake. A proposal to undertake fish rearing in enclosures on the lake was made and in July 1970 a 38-ha pilot fish pen was developed.
The pilot fish pen was constructed at Looc, Cardona, one of the fishing towns in Rizal Province (Fig. 2).
The fish pen was originally made of bamboo screens, supported in place by bamboo poles. The bamboo barricade enclosed the east and south boundary of the fish pen while a high elevated hill bordered its westerly shoreline. It has a 0.5-ha nursery enclosure of fine mesh net for initial rearing' of fish seeds to make sure that they do not escape through the bamboo screens. The bamboo screens were later replaced by polyethylene nettings after it was destroyed by a typhoon.
Initial stocking with 150 000 milkfish fingerlings was made in October 1970, equivalent to a stocking density of about 4 000/ha. A violent storm in November 1970 with winds up to 200 km/h destroyed 70 percent of the fish pen which resulted in the loss of the stock.
The project was rebuilt and on 17 January 1971, the same quantity of fish was restocked. They were given supplementary feeds in the nursery composed of a mixture of copra meal and rice bran for about two months after which they were released in the enclosure proper. Initial harvest of the stock took place in May 1971, after four months of rearing. The average fish size was 350 g and the average production was 700 kg/ha in four months. Such rate of production was nearly 3.5 times greater than the one observed in open waters and three times more than the national average yield of conventional brackish-water fishponds. This pilot project also showed that the milkfish could be reared entirely on the natural food supply of the lake (Delmendo and Gedney, 1976).
From 1971 through 1973 there was a rapid expansion of fish pen development on the lake, such that by the end of 1973 there were about 4 800 ha in operation.
The LLDA, by virtue of its powers and responsibility, has the “exclusive jurisdiction to issue permits for the use of the lake waters for any projects or activities in or affecting the lake including navigation, construction and operation of fish pens, fish corrals and the like and to impose necessary safeguards for water quality control and management and to collect necessary fees for said projects and activities. Provided, however, that implementation of all fisheries plans and programmes of the Authority shall require prior consensus of the Bureau of Fisheries to ensure that such plans and programmes are consistent with the national fisheries plans and programmes” (Republic Act 4850 as amended, 1975).
This mechanism, while it appears appropriate, encountered several administrative problems in actual practice and application of the law. The LLDA, being a regional development entity and a semi-government body, has to consult with national agencies, particularly the Bureau of Fisheries for programme coordination. Somehow, the desired coordination and complimentation of activities did not happen, resulting in communication gaps and confusion of the public. In the course of programme implementation, the information disseminated to the mass media did not spell out which agency should be consulted in matters of carrying out the development activities, such as the fish pen development of Laguna de Bay. People interested in going into fish pen ventures either went to the Bureau of Fisheries or the Laguna Lake Development Authority as the case may be, depending on whom an individual knows and what information was obtained. Consultations to iron out certain issues took time. Meanwhile, proliferation of fish pens already had taken place and not much could be done to correct the situation. The development plans as originally conceived did not take place in an orderly manner due to the lack of coordination of activities of the agencies concerned. The Bureau of Fisheries exercised its national prerogatives which jeopardized the plan of the LLDA.
What happened then was that non-resident individuals with financial resources of their own or with access to financing institutions occupied the choice areas for fish pen aquaculture. The small fishermen who were supposed to be the beneficiaries of the fish pen development became labourers but not the fish pen operators themselves. The LLDA lost control of the muncipal authorities under the provincial jurisdiction of the governments of Rizal and Laguna in view of the lack of coordination between the agencies concerned.
In 1978, the Asian Development Bank approved a proposal of the LLDA for financing fish pen development on the lake. The amount of the loan was US$ 9 million for the development of fish pen modules to be operated and owned by small fishermen in the lake area. The project envisioned a total of 2 500 ha of fish pens on the lake under the LLDA's supervision. The existing fish pens would be gradually phased out according to the fish pen development plan of the Authority. Fish pens outside the fish pen belt area would then be relocated.
Theoretically, a circular pen would be the least costly to construct because it yields the greatest area for the least length of perimeter fencing. However, such pens are wasteful of lake space because of the areas lost between adjacent pens.
The preferred shape is a square. Next to a circle, it yields the least cost requirement for fencing materials. For example, if we wish to build an enclosure with an area of 100 m2, this could be done as follows (Delmendo and Gedney, 1976):
| (a) | 10 m | × | 10 m | - | Perimeter | = | 40 m |
| (b) | 4 m | × | 25 m | - | = | 58 m | |
| (c) | 16.7 m | × | 6 m | - | = | 62.1 m |
Square fish pens have been constructed as small as 0.16 ha (40 × 40 m) to more than 100 ha. To be able to utilize the lake area effectively, some uniformity in size and layout with respect to spacing of adjacent fish pens are needed.
The size of fish pens varied from less than one hectare to more than 100 ha, the medium size being 10–20 ha. Smaller size pens of 5 ha provide more effective management than larger size pens. Large fish pens are subdivided into smaller units of 1–5 ha per compartment, depending on the total area of ownership.
Bamboo poles are the main structural element of the fish pen. The general details of construction are shown in Figs. 3 and 4. The poles must sustain the weight of the net screens and resist the lateral thrust of winds, waves and debris against the nets. The bamboo poles are driven at one meter intervals along the fence line. Driving is effected by shoving of 2–3 men utilizing their weight and working the bamboo sidewise while being pushed down. Batter poles (brace posts) are provided at every third to fourth post to minimize swaying of the fence. Recent experiences by fish pen operators showed the usefulness of cross-poles to counteract the effects of wind coming from opposite directions (Fig. 5). Double-fencing of fish pens also became an accepted practice as this provides extra protection against bad weather and also prevents poaching. The outer fence is enclosed by large mesh screens while the inner fence uses smaller mesh nettings. The cost of construction of this type of fish pen is much higher but operators still find it viable.
The nets come in rolls about 1.4 m wide and 50–100 m long. They are sewn together, both in width and length, using nylon thread. The top and bottom edges of the assembled nets are reinforced with nylon rope of 0.25 cm diameter. The bottom edge is provided with a second rope on which the sinkers, either of concrete blocks or pieces of rocks of 1 kg weight, are secured. Additional anchorage is achieved by pegging the bottom rope line with bamboo pegs driven into the lake bed.
The top of the screen net is provided with a float line (Fig. 6) sewn sectionally with floats to the enfolded rope. The screen is ordinarily fastened to the posts with two loops of No. 14 G-I-wire. However, in the above procedure, to minimize wave damage, the rope is hung on loops of wire from which the tie rope is disengaged in rough weather and the net is supported by the floats instead. In calm weather, the net is rehung to the hooks on the posts. Although the net is fabricated to provide full coverage from the lake bottom to the maximum water surface elevation, the height of the net is provided with a slack of at least 0.5 m to avoid submergence during high water level and to prevent fish from jumping out.
Recent designs do not use floats any more but simply a tie-line. The top edge of the net screens are tied to the bamboo posts at intervals of 1–2 m. This may be raised or lowered depending on the water level.
In 1973, the cost per hectare of enclosure ranged from P.Ps. 8 000 to P.Ps. 10 000 (US$ 1 000–1 370). At present (1979), it costs about P.Ps. 35 000 (US$ 7 000) to construct a hectare of fish pen. The actual costs are affected by the depth of the water; the lake bottom; size, height, shape and design of the enclosure; quality of construction; materials used; as well as by other factors such as labour cost. The estimated life of the materials used is presently 3–4 years with regular maintenance.
A stocking rate of 10 000–25 000 milkfish fingerlings/ha is practised without supplementary feeding. The size of the fingerlings should be large enough (8–13 cm) so as not to escape through the netting. If smaller fingerlings are used, a nursery is constructed inside the main fish pen (Fig. 7). The fingerlings are kept here for at least four weeks after which they are released in the fish pen proper. While in the nursery enclosure, they are given supplementary feed consisting of rice bran, copra meal and soybean. But as such feeds are quite expensive, the use of stale bread from bakeries is commonly practised.
After the fingerlings have been released inside the main fish pen, the fish stock subsists mostly on natural aquatic food. Thus, the main activity during the rearing period consists in maintenance of the structure and safeguarding the fish pen. Periodic inspection both above and below the water are needed to check on possible damages. Underwater checks require diving equipment to determine whether the bottom of the net is satisfactorily secured to the lake bottom.
The fish stock is harvested after 4–5 months of rearing in the fish pen. The growth rate is affected by stock density and availability of natural food. At 10 000 fish/ha the average size of fish at harvest is 0.3 kg.
Initially, gillnets are set for harvesting only the largest individuals. Later on, a drag seine is used to harvest the rest of the stock.
The harvesting of fish in the fish pen requires a long period of operation, particularly in large pens. The water level cannot be reduced as in the conventional fishponds. As a result of this, some operators block off a selected section of the fish pen for harvesting purposes. Custom labour is available in the lake area for harvesting fish in the fish pens.
The rearing period can be shortened if fingerlings are stocked in a nursery within the fish pen and brought to a size that will permit them to be released as soon as the harvest is completed. In a 20-ha fish pen, subdivided into four units, this would permit about one harvest each month, thus avoiding the hazards and problems of a single large harvest every 4–5 months. This system also tends to limit the lowering of market prices due to excess supply (Delmendo and Gedney, 1976).
Fig. 3 - CONSTRUCTION DETAILS OF A FISH-PEN ENCLOSURE: BAMBOO POLES AND NETTING FIXATIONS.
Fig. 4 - DETAILS OF CONSTRUCTION SHOWING THE NET RAISED (A-A) AND LOWERED (B-B) ACCORDING TO THE WATER LEVEL (SEE SECTIONS ON Fig. 3).
Milkfish is a highly rated fish for consumption. It is noteworthy that the 1973 production of 19 000 t from Laguna de Bay increasing from zero input in 1970 was fully absorbed in the Greater Manila and surrounding markets without gluts or depression of prices. As a matter of fact, milkfish produced from Laguna de Bay fish pens command better price than those obtained from brackish-water ponds. Their quality and condition are much better.
The wholesale price per kilogramme of milkfish compared to other fish in the Manila markets varied as follows, in P.Ps. (P.Ps. 7.3 = US$ 1):
| 1975 | 1976 | 1977 | 1978 | 1979 | |
| Milkfish | 4.50 | 4.80 | 7.00 | 7.00 | 8.00 |
| Mackerel | 4.80 | 5.00 | 7.20 | 7.50 | 8.20 |
| Tuna | 5.00 | 5.20 | 7.50 | 7.80 | 8.50 |
| Snapper | 6.50 | 6.80 | 8.00 | 8.50 | 9.00 |
| Grouper | 6.70 | 6.90 | 8.00 | 8.50 | 9.00 |
| Tilapia | 3.50 | 3.70 | 5.50 | 6.50 | 6.50 |
The population of the Greater Manila area and the market area around the lake are estimated to total approximately as follows (Delmendo and Gedney, 1976), in millions:
| Area | 1970 | 1973 | 1975 |
| Greater Manila | 4.2 | 4.6 | 9.2 |
| Lake - Regional Markets | 0.8 | 0.9 | 1.4 |
| TOTAL | 5.0 | 5.5 | 10.6 |
Per caput annual consumption of fish in the Philippines is about 30 kg. It is estimated that by 1985 the population of the lake region would increase by 2.1 percent from the 1973 figures. Because of an increased standard of living coupled with an emphasis on protein food sources close to a 10 percent increase, it is expected that by 1985 the market demand for fish will increase by about 2.3 percent (Delmendo and Gedney, 1976). The lake is so close to the Manila and suburban markets and is as well a source of fish for the northern parts of Luzon Island.
Actual experience in fish pen operation by the author and the results obtained from the LLDA project showed that aquaculture in fish pens on Laguna de Bay is a highly viable one, despite the high risks involved. A 5-ha fish pen in 1972 recovered 36% of its total stock before a big flood and was still profitable after 100% depreciation of the structure.
The performance of the LLDA project since 1971 is shown below (pers. comm. LLDA, 1979):
| Year | Fish Seeds | Percent Recovery | Fish Yield | Yield Valuea | ||||
| Number | Unit Cost (P.Ps.) | Total Cost (P.Ps.) | Average Weight (g) | Total Weight (kg) | Per kg (P.Ps.) | Total (P.Ps.) | ||
| 1971 | 150 000 | 0.05 | 7 500 | 58 | 320 | 28 000 | 3.00 | 74 880 |
| 1972 | 250 000 | 0.06 | 15 000 | 70.2 | 350 | 61 494 | 3.50 | 215 229 |
| 1973 | 300 000 | 0.08 | 24 000 | 64.4 | 250 | 54 870 | 4.00 | 219 480 |
| 1974 | 385 000 | 0.10 | 38 000 | 86 | 330 | 50 385 | 5.00 | 251 925 |
| 1975 | 585 000 | 0.11 | 64 350 | 28 | 250 | 45 402 | 4.50 | 204 309 |
| 1976 | 500 000 | 0.16 | 80 000 | 22 | 180 | 45 403 | 4.80 | 217 934 |
| 1977 | 552 000 | 0.18 | 99 000 | 60 | 300 | 99 486 | 7.00 | 696 402 |
| 1978 | 585 000 | 0.23 | 134 550 | 73 | 220 | 48 618 | 7.00 | 271 928 |
The costs of fish seeds increased gradually from year to year by P.Ps. 0.01–0.02 per fingerling, except in 1976 and 1978 when there was an increase of P.Ps. 0.05 a piece. The average size of fingerling is 6–10 cm long weighing 5–10 g each. The price of milkfish in the market increased by P.Ps. 0.50–1.00/kg each year, except in 1977 when an increase of P.Ps. 2.20/kg occurred. This could be attributed to the increase in the cost of gasoline, labour and materials. The cost of transport of fingerlings from the source increased by about 50 percent.
A detailed input-output analysis of the LLDA project in the year 1978 showed a net return of 28.57 percent of gross income and 39.99 percent of operating costs, as follows:
| A. | Gross sales | P.Ps. | ||
| Milkfish, 48 618 kg at P.Ps. 7.00 | 271 928.81 | |||
| B. | Expenditures | |||
| Salaries and Wages | 46 443.97 | |||
| Medical Insurance | 337.50 | |||
| GSIS premium | 1 121.35 | |||
| Fish seeds | 134 550.00 | |||
| Office supplies | 385.00 | |||
| Travelling expenses | 2 316.35 | |||
| Repair and maintenance | 2 005.70 | |||
| Communication | 7.20 | |||
| Sales discount | 4 451.80 | |||
| Harvesting and marketing | 2 623.50 | |||
| TOTAL | 194 242.34 | |||
| C. | Net total income | 77 686.47 | ||
| Net income/ha/year | 2 044.38 | |||
| Average production (kg/ha) | 1 279.40 | |||
The net income is higher than the conventional extensive brackish-water fish farming of milk-fish in the country where average production is 500 kg/ha.
The LLDA fish pen produces one fish crop a year on account of the large area under operation. Complete harvesting is not possible in a short period. The growing period takes 4–5 months and harvesting the stock takes 2–3 months. If the 38 ha fish pen is subdivided into smaller compartments of at least 5 ha each, one enclosure could be stocked twice a year and produce more than now. Smaller fish pens of 0.16–5 ha showed production levels much higher than larger enclosures (Table 1).
5.3.1 Typhoons
The Philippines has a monsoon season which is accompanied by storms and typhoons of varying intensities. This occurs during May to December, every year. In Laguna de Bay area, for example, the percentage distribution of typhoons of high intensity (signal No. III with winds of 150–190 mph) is as follows:
| Month | % |
| January | 1 |
| February | 0 |
| March | 0 |
| April | 1 |
| May | 3 |
| June | 5 |
| July | 15 |
| August | 25 |
| September | 23 |
| October | 15 |
| November | 10 |
| December | 1 |
It was calculated that the probability of Laguna de Bay being hit directly by strong typhoons of No. III intensity is one out of four or once in eight years The first typhoon of this magnitude did hit the project in 1970 (typhoon “Yoling”) which destroyed 70 percent of the pilot project. Since then, there were other typhoons of similar intensities but they did not directly hit the area. Damages to fish pens occurred but nevertheless did not discourage the operators from coming back into operation each time.
5.3.2 Floods
Monsoon rains take place for several days (7–10 days) of continuous rainfall. As a result of this, rivers overflow and the water level of the Laguna de Bay Lake increases.
Fish pens that are not provided with adequate allowance for highest water levels are apt to be flooded and may lose their fish stocks. The fish pen operators have now been prepared for this eventuality. At least 0.5–1 m allowance above the highest lake level is provided in the construction of fish pens. Flooding occurs during August to November, when the frequency of typhoons hitting the area and the rainfall are greatest.
5.3.3 Fish kills
During summer, the lake level is low or equal to mean sea level. At this time, the lake becomes stagnant and high densities of algae predominate, particularly Anacystis neroginosa. Sometimes, this algal population explodes and the lake water looks like pea soup. The breakdown of this algal mass takes up the dissolved oxygen and results in fish kills. This happens during the months of April, May and June when water temperature is high and the lake level is low. Fish pens are usually intensively stocked and, if not carefully watched, losses due to fish kills occur. Algal biomasses of 110.6 g/m3 have been observed in 1974 as shown in Fig. 8. Knowing this phenomenon and its occurrence in the lake enables the fish farmers to schedule their harvesting and stocking accordingly.
Fig. 5 - CONSTRUCTION OF THE FENCING FRAME WITH BAMBOO, USING LATERAL REINFORCEMENT.
Table 1
Stocking density, fish yield and survival in fish pens
(from Delmendo and Gedney, 1976)
| Sample No. | Area of Enclosure (ha) | Total Stock (N) | Density (N/ha) | Culture Period (mos) | Survival (%) | Yield | Averagea Weight (g) | Per Crop Production (kg/ha) | |||
| W (kg) | N | ||||||||||
| 1A | 38b | 380 000 | 10 000 | 5 | 33 | 49 | 500 | 125 | 400 | 400 | 1 302 |
| 1 | 38 | 120 000 | 6 000 | 5 | 48 | 23 | 400 | 57 | 000 | 411 | 585c |
| 2 | 5 | - | - | 5 | - | 8 | 387 | 18 | 750 | 448 | 1 677 |
| 3 | 0.50 | 11 000 | 22 000 | 4 | 82 | 2 | 030 | 8 | 990 | 226 | 4 060 |
| 4 | 0.30 | 30 000 | 103 448 | 6 | 47 | 5 | 135 | 14 | 101 | 365 | 17 706 |
| 4-B | 0.30 | 25 000 | 86 207 | 5 | 65 | 3 | 401 | 16 | 083 | 212 | 11 728 |
| 5 | 0.25 | - | - | 5 | - | 660 | 5 | 640 | 117 | 2 640 | |
| 6 | 0.16 | 10 000 | 62 500 | 6 | 87 | 2 | 030 | 8 | 620 | 236 | 12 688 |
| 6B | 0.16 | 15 000 | 93 750 | 5 | 22 | 914 | 3 | 193 | 287 | 5 714 | |
| 7 | 0.40 | 7 000 | 17 500 | 5 | 75 | 619 | 5 | 250 | 118 | 1 548 | |
| 8 | 0.29 | 10 000 | 68 966 | 6 | 31 | 1 | 661 | 6 | 032 | 276 | 5 728 |
| 9 | 0.50 | 50 000 | 100 000 | 5 | 29 | 2 | 142 | 14 | 300 | 150 | 4 284 |
a Average = 259 g
b Sub-divided into 3 compartments of 8, 13 and 17 ha each
c Reflects algal bloom mortality
Fishermen around the lake found alternative employment in the construction of fish pens; custom group labour in the harvesting of fish stocks was developed, and employment as caretakers or security guards in fish pens are some of the new employment activities opened to the fishermen and their family members. Where before they were subsistence fishermen, the advent of fish pen development gave them a more permanent source of income. Fishing is now a part-time occupation in open waters of most fishermen.
Buying and selling fish became a brisk trading activity of many housewives and couples in the lake area. The transportation business increased and the production of block ice also increased tremendously. The selling of ice and fish containers increased.
Young children after coming from school spend their time in cleaning bamboo materials in preparation for fish pen construction. They earn their pocket money easily at P.Ps. 0.05 a piece of whole length bamboo, cleaned of its rough nodes and spines. A young boy of ten years old could earn as much as P.Ps. 5.00 as part-time work.
The bamboo tree, which used to be taken for granted, left unattended and could be had for the asking before the fish pen development became a precious plant afterwards. Landowners with bamboo groves cut bamboo trees selectively. Bamboo-growing is a source of good income of families with few bamboo stands in their land. The trucking of bamboo went as far as the northern Luzon provinces to meet the demand of fish pen operators. The quiet towns bordering the lake suddenly became alive and teeming with economic activities. There were several options open to the people for livelihood and sources of income. The forward and backward linkages of economic development with the fish pen as the nucleus was very evident. The social and economic conditions of the people greatly improved and the majority of them are no longer on subsistence level of living.
Before the fish pen development, the lake fishery was very poor in quality. The desirable species were practically on the verge of depletion. The landlocked catfish (Arius sp.) became a delicacy because of its high price, its high demand and scarce supply. Since the fish pens developed, the catfish fishery became abundant and the price per kilogramme, although still relatively expensive, became again within the reach of the people. It is now available on the market in reasonable quantities. The silvery perch, which used to be available in very small sizes, have grown to desirable quality.
All these were brought about by the fact that fishing intensity decreased and the fish pens served as sanctuaries for the natural fish species; they could reproduce successfully and grow to a desirable size before being caught. Open water fishing now is becoming profitable again. The fish pens, therefore, made it possible to implement conservation measures which the fishery rules and regulations did not succeed to achieve in the past.
Fig. 6 - A FISH-PEN ENCLOSURE MADE OF NETTING MATERIAL, IN THE RAISED POSITION.
Fig. 7 - THE ORIGINAL SMALL NURSERY ENCLOSURE INSIDE THE FISH-PEN FOR REARING SMALL FINGERLINGS, MADE OF BAMBOO SCREENS.
Fig.8 - Total Phytoplankton Biomass of Laguna de Bay, 1973–1977
Source: Final Report, Comprehensive Water Quality Management Programme, LLDA/WHO Vol. 5, May 1978
The present performance of fish pen production in Laguna de Bay shows the highly productive and profitable operations. From the viewpoint of biological productivity and market demand it is estimated that the area of the lake in fish pens can be increased from the present coverage of 4 800 ha up to 20 000 ha. Improvement of design and construction and the techniques of management can definitely result in higher production. Table 2 shows the potential of the lake for increased production with increased areas of fish pens with year 1973 as benchmark.
The lake has a very high primary productivity which is accompanied by a high recycling speed. This explains the enormous secondary productivity (fish, shrimps and snails) of Laguna de Bay which has not yet reached its potential limits. Studies by the LLDA showed that only 5–7 percent of the standing crop in terms of nitrogen is converted into fish flesh (Final Report, Water Quality Management Programme, Vol. 4, May 1978).
The current loan granted by the Asian Development Bank to the LLDA for fish pen development envisages 2 500 ha. At full development, self-employment for about 1 500 fishermen families representing about 9 300 individuals is foreseen. It is also expected to increase the annual income of the loan participants from less than P.Ps. 9 000 to a range of P.Ps. 18 500 to P.Ps. 41 700 (ADB News Release, 1 December 1978).
Table 2
Potential of fish pen production in Laguna de Bay
| Year | Area (ha) | Yield (t) | Value (P.Ps. million) |
| 1973a | 4 802 | 19 000 | 77 |
| 1978 | 6 000b | 24 000 | 168 |
| 1985 | 8 500c | 34 000 | 255 |
a Delmendo and Gedney, 1974
b Estimate based on recent personal observations
c 1978 area plus ABD project
The degree of intensification being attained by fish pen operators requires not only a system of fish seed nurseries to develop a dependable supply all year round but also species diversification. This would take full advantage of the food chain that exists in the lake. A species of fish that would help graze on bluegreen algae, particularly Anacystis, would further increase the output of fish pens. Tilapia has already shown compatibility with the milkfish in this type of aquaculture. Diversification of species would not only utilize the available food materials but would also lessen the high demand for seeds of milkfish. Competition for seed supply resulted in increased prices of milk-fish fingerlings from P.Ps. 0.15 to P.Ps. 0.40 each. As a consequence of the stiff competition for fish seeds, some fish pen operators shifted to tilapia. The brackish-water fishpond operators used to poison tilapia in their ponds. However, as a result of the high demand for fish seeds, the tilapia fingerlings which practically did not have any value before, now has a competitive market value.
Periodic algal blooms occur on the lake which cause “fish kills” and heavy losses to fish pen operators such as that which happened in 1973 and 1975.
Studies have shown that although the nitrogen and phosphorus content of Laguna de Bay were high, nitrogen was found as the main stimulant of algal blooms. The sources of nitrogen include agricultural, industrial and domestic wastes. The control of nutrient inflow is possible, however; this requires a costly management programme. The LLDA had established a water quality laboratory with the assistance of the United Nations Development Programme and ADB. The work programme initiated in this laboratory, however, needs a more dynamic technical leadership and sustained manpower development to carry out its tasks. Unfortunately, there has been a rapid turnover of personnel stemming from a lack of adequate incentives and job security. The management seems to overlook the importance and value of keeping trained technical staff.
The control of toxicants from 120 industrial plants located in the watershed is also necessary if the use of the lake for water supply and fisheries production is to be maintained for an indefinite period.
The construction and operation of fish pens is now capital intensive. Prices of construction materials and fish seeds have increased tremendously and only individuals with strong financial resources could still afford pen culture. The lake fishermen were practically eliminated from fish pen entrepreneurship, aside from losing their traditional fishing grounds. On the other hand, the fish pens helped rehabilitate the open water fishery after a few years of development. This benefit somehow compensated for the loss of previous fishing areas. The quality of fish being caught in the open waters is much better than it used to be but the economic returns to fish pen operators are definitely much higher. Fishermen are residents of the lake shore communities around the lake, whereas fish pen operators are from outside the lake area. The benefits of fish pen development are, therefore, directly obtained by non-residents.
The Philippine Bureau of Fisheries and the LLDA were not able to agree upon and implement an effective programme after the successful demonstration of the pilot fish pen project.
The basic policy which the LLDA attempted to implement was not fully supported at a national government level which resulted in the proliferation of fish pens. There was chaos in the issuance of permits for construction of fish pens to the extent that overlapping of rights occurred in certain areas ending in court cases to settle water rights for fish pen development.
A sustained programme of monitoring the water quality of Laguna de Bay must be pursued. The control of industrial wastes around the lake must be implemented. Information and essential data for water quality management and pollution abatement are available as basis of government support.
The lake should be zonified for purposes of locating fish pens and permit adequate circulation and movement of water. As the existing fish pens would be difficult to relocate, the construction of new ones should take into consideration proper layout and design.
The implementation of the recently approved loan from the ADB for fish pen development should give priority to the small fishermen living in the lake area to engage in fish farming. This would foster opportunities to fishermen to share the benefits of fish pen production.
The experience in the Laguna de Bay aquaculture operations demonstrates the feasibility of fish farming in natural waters. The technology developed in the area has possible applications in many bodies of water in similar situations. In Southeast Asia there are approximately 60 000 ha of reservoirs; 220 000 ha natural lakes and about 180 000 ha rivers and marshes (Fernando and Furtado, 1975). These water surface areas could be harnessed for food production through aquaculture. The increasing demand for protein food supplies in most developing countries warrants transfer of this technology elsewhere. It is, however, necessary that the natural productivity of the bodies of water be known prior to utilizing them for aquaculture development. This would determine the species appropriate for use in the fish pen without disturbing the indigenous fisheries in the body of water.
The social, economic and political environments under which the use of such water areas operate should be carefully studied in order that conflicts of interests between national and local government agencies could be avoided.
Inland waters are in most instances public properties. The use of these waters for aquaculture and fishery production should be limited to fishermen so that this sector of society, which is considered the lowest class in many developing countries, would have the fair chance of social and economic improvements at some points in time of their difficult lives.
The institutional framework under which fish pen aquaculture should operate should take into consideration the involvement of local governments as they are more familiar with local conditions, the peace and order situation, and the rural population that should be the beneficiaries of such development. In agriculture, land reforms have been implemented. The counterpart of this programme in fisheries should give development bias in favour of the small fishermen in inland or coastal areas.
Technical servicing of aquaculture development in natural waters is the responsibility of national research institutions and regional development agencies. However, the management and administration of development could be handled by the local governments with the technical support of regional/national development agencies. This linkage is often mentioned in public but so far has not been found in practice. The framework under which aquaculture development in natural bodies of water would differ from country to country. The most appropriate mechanism that would promote the socio-economic development in rural areas would be one that has the involvement of the rural people (fisherman/farmer) and village institutions in development planning and implementation. National/regional agencies should provide technical backstopping and monitoring of the development activities. This mechanism should in effect have a two-way flow of communication and information dissemination up and down the line and vice versa. Under such a situation the problem-solving and decision-making process would cut across the local and national government machineries concerned. Everybody is involved and there would be no competition and overlapping of activities.
The LLDA, being a regional development agency which is partly funded by local funds from both the provinces of Rizal and Laguna, requires strengthening of its technical and administrative capability in order that it could adequately respond to the needs of the aquaculture development on the lake and liaise with the national research agencies for better technical cooperation and collaboration of work.
Delmendo, M.N., 1966 Food and feeding habits of economic species of fish in Laguna de Bay. Proc.IPFC, 13(2):143–61
Delmendo, M.N., 1966a An evaluation of the fishery resources of Laguna de Bay. Paper presented to the Twelfth Session of the IPFC. Honolulu, Hawaii, USA, 3–17 October 1966. Bangkok, IPEC, IPEC/C66/Tech. 40
Delmendo, M.N., 1974 Fish farming in pens - a new fishery business in Laguna de Bay. Tech. Pap.Laguna de Bay Auth., (2) (mimeo)
Delmendo, M.N. and R.H. Gedney, 1976 Laguna de Bay fish pen aquaculture development - Philippines, Proc.Annu.Meet.World Maricult.Soc., 7(1974):257–65
Delmendo, M.N. and T. Shimura, 1968 A report on the listing survey of duck farms and fishing families of Laguna de Bay. Unpubl. (mimeo)
Fernando, C.H. and J.I. Furtado, 1975 Reservoir fishery resources of south-east Asia. Bull.Fish.Res.Stn.Sri Lanka, 26(1–2):83–95
Rabanal, H.R., P. Acosta and M.N. Delmendo, 1964 Limnological survey of Laguna de Bay - a pilot study on aquatic productivity. Paper presented to the Eleventh Session of the IPFC, Kuala Lumpur, Malaysia, 16–31 October, 1964. Bangkok, IPFC, IPFC/C64/TECH 46
