Bangus production varies from zero to an excess of 2,500 kilograms per hectare. Many factors must be considered when evaluating management. Some places are so poorly designed that practical operation is impossible. It is as important to recognize that there are places where we cannot produce fish economically, as it is to recommend good cultural practices.
When we visit a pond site our first job is to examine the management history. The most important aspect of extension is collection of data pertaining to the past and current management of the production facilities. We cannot recommend better management unless we understand how the ponds have been managed in the past. A form for this (Exhibit 1) identifies the site and collects the information in an orderly fashion.
| (3 copies) | |
| -Reg. Office | |
| -Ext. Worker | |
| -Owner/Mgr. | |
| -Provincial Programme Off. |
MANAGEMENT Exhibit 1
Location
Owner/Manager
Address
How long in business?
What species?
What does the owner/Manager consider to be the problem area?
What pond preparation is used?
Where do the fry/fingerling come from?
What handling techniques are used?
How many fry/fingerling stocked per hectare?
What provision is made for multi-crop production?
What fertilization programme?
What food type is produced by fertilization (does it change during growing season?)
What harvest system is used?
What is the average production? (kg/ha/year)
What is the water chemistry?
Salinity pH Hardness Mg ppm
C1 ppm Ca ppm Fe ppm
What soil types? Sandy Sandy loam Loamy sand
Loam Silty loam Silt
Soil analysis/sent to lab. date
Analysis sheet attached?
Pest problems?
Pest control methods?
Disease problems?
Supplemental feeding
Building and equipment
Labor force Permanent
Seasonal
Other information
A month or two before the nurseries are stocked and/or before the arrival of the new supply of bangus fry for the whole year for the fishpond project, the nursery, transition, formation and rearing ponds are prepared in the following way:
Draining and drying is done by completely draining the pond of its water and allowing it to dry for about a week or more depending upon the weather conditions prevalent in the locality.
Pond soil should be dried every time the pond is harvested. Periodic drying stabilizes soil colloids and oxidizes organic matters and thus prepare a suitable environment for the growing of the natural fish food.
The purpose of draining and drying are:
To eradicate fishpond pests, predators and competitors;
To hasten the chemical decomposition of organic matters deposited so that nutrients will become available for the growth of fish food in the fishpond;
To totally harvest the fish stock; and
To kill fish disease organisms.
As soon as the pond system has been drained during low tide, the pond bottom is immediately tilled and cultivated. This is done by stirring or cultivating with a shovel or a rake for a small pond and by the use of rotavator for large ponds.
The purpose of tilling or cultivating are:
Subsurface nutrients are made available at the surface for the growth of fish food in the pond;
Burrowing fish enemies are eradicated; and
Undesirable pond weeds are eliminated and destroyed.
After the pond bottom has been tilled and cultivated, all holes, mounds and depressions on the pond bottom are leveled. The purpose is to make the topography of the pond bottom slope very gradually from its farthest end down towards the gate, the deepest portion of the pond. After the pond bottom has been leveled, a narrow canal within each pond or compartment that runs from the gate traversing towards the opposite corner will be made and maintained. The canal will gradually deepen towards the gate. The canal will serve as a refuge for the fish during the hot season and also for confining fish before their transfer to another pond, or before they are harvested. Since the canal serves as a refuge, predators and pests could also be confined in it for easy eradication.
During the drying period of pond bottom systems, all dikes should be checked for leakages. Supply canals are cleaned of debris and other unwanted materials and are deepened to facilitate easy and even flow of water to and from the pond system. Vegetation on the dikes should be cleared and eroded dikes should be patched. All dikes must be water tight.
All gates whether concrete, semi-concrete and wooden are checked every now and then for their efficiency in letting in and out of the water. Barnacles, oysters and other shells that attach to the gate are taken out; weak wooden gates are totally repaired including the coarse and fine screen before the beginning of the culture period to prevent or minimize predators and pests from entering the pond system.
Fishpond fertilizers are organic and inorganic substances applied to pond waters and soils to stimulate and maintain growth of plants. In ponds the desired plants are the various forms of algae that, along with small animals, compose lumut, lab-lab or plankton -- the foods of fishes.
Foods of algae are carbon dioxide, water and minerals. Algae obtain carbon dioxide from the water and not directly from the air as land plants do. Water is the major substance used by algae composing as much as 90% of the total weight of some algae species. Algae get all of their foods from pond water because carbon dioxide and minerals are dissolved in the water. There are 16 different minerals essential as algae food but most of these are abundant in pond waters and soils. However, an available form of phosphorus (P) is almost always in very low amounts in ponds, nitrogen (N) is very often in low amounts, and potassium (K), calcium and magnesium are sometimes in low amounts.
Fertilizing ponds to supply the nutrients in short supply and limiting plant growth is a fundamental part of fishpond management. Fish production per unit area can be increased as much as five fold or more by the proper application of mineral fertilization. Generally, N-P fertilizers are the only minerals recommended for fishponds. Often P is the only mineral that must be added to obtain maximum fertilizer efficiency.
Organic fertilizers most commonly used in fishponds are animal manures, especially chicken manure, but organic materials of other sources are also used. Composts, rice bran, grass and sewage as well as animal manures are popular organic fertilizers used in fishponds in various parts of the country.
Inorganic fertilizers are chemical fertilizers containing concentrated amounts of at least one of the three major plant nutrients -- N, P and/or K. A common single-element fertilizer used in fishponds is 0–20–0 (superphosphate); common incomplete or two-element fertilizers used in fishponds are 16–20–0 (monoammonium phosphate) and 18–46–0 (diammonium phosphate).. An example of a complete fertilizer is 14–14–14 but complete fertilizers are almost never recommended for fishpond use because sufficient amounts of K are almost always present naturally in fishponds and adding more K as fertilizer is not beneficial.
Fertilizer grade numbers are printed on the bags of inorganic fertilizers and represent the amount, in percent by weight, an 18-46-0 grade fertilizer contains 18% available Nitrogen (N), 46% available phosphate (P or P2O5) and 0% available potash (K or K2O). Some mixtures of inorganic fertilizers contain sulfur (S) which may be indicated on the bag as with, for example, ammonium sulfate written as 21-0-0-23 (N-P-K-S).
Methods and practices - For lab-lab production, fertilizers may be added to the bottom soils prior to or after flooding with water. After flooding and stocking fish, inorganic fertilizer may be added at 15 - to 20 - day intervals to sustain and rejuvenate lab-lab growth.
For production of plankton and lumut, inorganic fertilizers are sufficient and are likely to be more efficient in old ponds than organic fertilizers. Single-element phosphate fertilizers are likely to be sufficient in maintaining growth of all types of algae in old ponds. Fertilizers should be added after flooding the pond to culture depth.
Application of fertilizers will be needed every 15–30 days. To obtain optimum algae production, visual observation of the algae being cultured will indicate if fertilizer is needed, like if growth diminishes. In ponds with phytoplankton, fertilizer is necessary when the green growth in water clears to the extent that white objects placed in the water can be seen at 40 cm depth.
Broadcasting fertilizer evenly over the pond bottom prior to and after flooding is the standard technique for fertilizing lab-lab ponds. Platforms positioned 15 to 20 cm below the water surface are effectively used for fertilizing fishponds with inorganic fertilizers. Water currents distribute the nutrients throughout the ponds. This method requires less labor and less fertilizer than broadcasting.
The following programs have been used successfully for producing lab-lab and plankton.
| Fertilizer | Amount per Application | Method and frequency of application | |
| Plankton | Lab-lab | ||
| 18-46-0 | 22 kg/ha | Apply all applications on a platform | Apply first application by broadcasting and all follow-up applications by broadcasting or on a platform |
| 16-20-0 | 50 kg/ha | Apply every 15 to 30 days or as needed to keep water visibility between 20 to 30 cm. | Apply every 15 to 30 days |
| Chicken manure | 2000 to 2500 kg/ha | Apply only in new ponds or in ponds that have little or no “soft organic mud”. Apply by broadcasting. Use only when preparing pond and use 18-46-0 or 16-20-0 in follow-up applications as recommended above. | |
In ponds older than three years, 0-46-0 or 0-20-0 may possibly be substituted for 18-46-0 and 16-20-0, respectively, after the first application.
Preparation of the nurseries for the production of the lab-lab
A month or two before the nurseries are to be stocked, they must be prepared with meticulous care. The object of the preparation is to create the best conditions for lab-lab growth, and to completely eradicate the enemies and competitors of the fry.
First the ponds are leveled. Sometimes it becomes necessary to do some preliminary cultivation or stirring of the bottom soil in order to make leveling more convenient. The topography of the bottom should be so made that the gate or that place around the catching basin area (kulungan) is the lowest. Then the elevation rises very gradually towards the edges of each pond. Some nursery caretakers provide a canal running diagonally from the gate area towards the opposite corner in order to prevent wholesale death of fingerlings in case of a mistake in draining and to provide fish shelter during warm days.
Once ponds are properly leveled they are ready for drying. They are therefore drained completely during low tide and the gates are closed by putting temporary soil diking to keep out water. The bottom of these ponds is exposed till the soil cracks with dyrness. This may be accomplished within a week to even two-month period. Sometimes it becomes necessary to admit new water during high tide and to let this water drain out again thereafter. This practice has been found to induce burrowing animals, such as species of eels, to come out to the surface where they die when the pond dries again. It also hastens the transformation of the organic matter to the nutrients necessary for the growth of lab-lab.
Within a week to a month before stocking, new tidal water is allowed into the pond to a depth sufficient to cover the pond bottom (about 3 to 10 cm.). At this time the gates are well-screened by covering the bamboo screens and pipes with finemeshed abaca cloth (sinamay) to prevent the entrance of predatory species. This regulated height of the water is maintained except for occasional freshening with new tidal water. Under these conditions a luxurious lab-lab growth can be maintained until the fry are planted.
Requirements for growing of fish food2 - For the proper and continuous growth of lab-lab, the following factors should be taken into consideration:
Depth of water
Nature of the soil
Frequency of freshening with new tidal water
Density of fish stock and the presence or absence of other organisms utilizing lab-lab for food.
For the proper growth of lab-lab, the water in the pond should be kept not more than 12 centimeters deep most of the time. If the water is too deep or beyond 12 centimeters, filamentous green algae may develop and curtail the growth of lab-lab.
The most suitable soil observed for lab-lab growth is clay, sandy clay or loam. Sandy or rocky soil is not suitable.
Since the organisms composing lab-lab also need food, frequent freshening, however, should be handled in such a manner that the bottom is not much disturbed stirred by the current produced.
Certain other factors need to be considered in managing a pond for lab-lab production. Turbid waters have been shown to give poor results. The pH for normal growth of lab-lab has been observed to be slightly acidic. Brackishwater is better than the too saline marine water or the fresh water from the rains. High temperature do not hinder lab-lab development.
To maintain a continuous supply of lab-lab the pond should not be overstocked with fry. Ordinarily thirty to fifty fry per square meter is a reasonable stocking. When ponds are over-stocked the lab-lab is exhausted and the fish become stunted, mortality is increased, and diseases may develop. Efforts should be made to eliminate other organisms feeding on lab-lab. These organisms include molluscs, crustaceans and other species of browsing fish.
Soil acidity limits the production of natural fish food by limiting the availability of plant nutrients, and in extreme case cause fish kills. To ensure fish production the control of acidity is of primary importance.
Vegetation - areas where the original and dominant vegetation is bacauan (Rhizophora) and mangrove species producing tannic acid.
Soil sulfides - during the process of excavation and leveling of pond bottom layer of soil containing sulfur (acid zone) are disturbed or brought up and the oxidation of soil sulfides produces sulfuric acid.
Run-off - acid elements wash away from upland and carried into the intertidal zone. Also from fishpond dikes whose materials contain acid and washed during heavy rain.
Leaching - during the process of drying pond bottoms, acid forming elements are exposed to air and sunlight, and by oxidation will combine with water or form precipitates. Acidity is significantly reduced by washing or flushing pond bottoms. This process is effective in slightly acidic soil. In extremely acidic soil, it will take a longer time to correct acidity.
Liming - Lime efficiency: The theoretical neutralizing efficiency of lime is based on that of pure calcium carbonate (CaCO3), it being assigned a value of 100%. A second factor which becomes important when evaluating the actual efficiency of lime is the size of the particles. The larger the particles the slower the materials will react in the soil, and the less its actual efficiency. There are three commonly used forms of lime:
Unslaked line (CaO or quicklime), manufactured by heating crushed limestone and seashells is the fastest acting form. It has an efficiency rating of 173% CaCO3. Its known use is to control soil and water acidity, and pond pests and diseases. (Caution in handling).
Slaked lime (Ca(OH)2 or Hydrated lime) also a burned lime with water added, has an efficiency rating of 135% CaCO3. It is also fast acting.
Agriculture lime (CaCO3 or dolomitic lime) is crushed limestones or shells. Its theoretical efficiency is less than 100%. This material is relatively slow acting but due to its comparatively low cost and ease of application, it may be best for long term control of soil acidity.
Soil analysis - the needs of pond soil should be properly evaluated to determine whether lime is needed. Then the rate of application or lime requirement must be established. Knowing the proper rate of lime application is important to prevent overliming, minimized expenses, and possible loss of phosphate from pond waters through the formation of insoluble calcium compounds.
Application of lime - Lime is broadcasted or spread over the drained but moist bottom. The lime should be worked in or thoroughly mixed with the soil to attain maximum effectivity. Sufficient time or about week or two after applying the lime is allowed to elapse before the application of phosphate fertilizer.
- The benefits of adding lime and methods for determining the optimum rate of application have not been fully established. However, some degree of success has been experienced by many successful fish farmers all over the country.
Several studies show that soft pond bottom with pH of 6.8 favor rapid growth of green and blue-green algae. Those with less than 6.5 should either be washed or treated with lime depending upon the degree of acidity. This probably should be a good “rule of thumb”. Some practical ways of determining soil acidity:
Identify acid problem pond
A newly excavated pond is likely to be acidic.
Ponds that do not respond to fertilization.
Ponds with plenty of decaying becauan roots.
Pond bottoms that turn reddish when exposed to sunlight for more than three days.
Evidence of “JARSITE”, could be identified by the yellow color of the soil at some portion of the dike.
Determining soil pH colorimetrically
There are several mixed indicator systems for determining soil pH (some are more accurate than others). Commercial preparations are available or the ingredients may be purchased and mixed.3
Preparation:
Dissolve4 in one liter of distilled water
0.8 g Bromothymol blue indicator
0.4 g Methyl red powder
0.2 g Methyl orange powder
Use:
Place a small quantity of soil on a white porcelain plate and mix it with several drops of the indicator, then tilt the plate so that excess liquid flows away from the soil. Observe the color.
| Red | - very acid | pH = 4.0 or less |
| Yellow | - acid | pH = between 5.0 and 6.0 |
| Green | - neutral | pH = 7.0 or above |
- About ½ ton of dolomitic limestone per hectare is needed to raise the pH 0.1 when the soil pH is below 7.0. To calculate the amount of unslaked lime, divide the total amount by 1.73, or if slaked lime is used divide by 1.35. Example: Pond bottom soil pH = 6.2 Desired pH = 6.5
| 6.5 | |
| - 6.2 | 3 × .5 = 1.5 Tons Agricultural (dolomitic) Lime |
| 0.3 | or 1.5 ÷ 1.73 = 870 K unslaked lime |
| or 1.5 ÷ 1.35 = 1,100 K slaked lime |
Pests include fish, snails, crabs, insects and vegetation. Pond preparation, drying, liming, leveling and gate repair all contribute to pest control. Despite pond preparation, some pests will still enter the ponds. Crabs and snails move over dikes and levees. Fish eggs and fry come through screens. Insects deposit eggs in the pond area, and some insect larvae feed on small fish and fish food organisms. Many pests compete for food with the production species. Other pests compete with natural food production by either disturbing the pond mechanically, or interrupting the food chain. The following are some pest control measures:
- Apply hydrated lime to kill surviving animals. Lime application for soil conditioning will also serve to control pond pests.
3 Only a small amount of the mixed indicator should be dispensed.
4 If the sodium salts of these powders are not available, they may first have to
be dissolved in a small quantity of ethyl alcohol.
- Water boatmen, backswimmers, mosquito larvae, and other insects that require atmospheric air for survival can be killed by use of an oil slick. Mix one liter used motor oil, one half liter kerosene, one half liter used cooking oil per hectare. Cast evenly around two sides of the pond on a calm sunny day after 10:00 AM and before 12:00 noon. If a light (not above 4 knots) breeze is blowing cast the oil on the water on the windward side. Oil treatment should be done to ponds adjacent to the problem pond to prevent rapid reintroduction of insect pests. When the oil mixture blows to the edge of the pond it will kill young vegetation.
- Fish pests should be trapped at the main gate and secondary gates. Canals should be poisoned using rotenone 2 ppm (parts per million) during times when it is not necessary to use water for a week or more. Established population of fish pests such as tilapia can be trapped in the growing ponds using feed as bait. Partial poisoning of larger pond (5 hectares and above) in the spawning area of the pest fish.
Illus. 1
is to fix a net across the leeside corner that is used by tilapia as a spawning area (Illus. No. I). Calculate a total pond treatment of 0.25 ppm. Use this amount of rotenone (derris root or a3) solution broadcast over the spawning area. Saleable size fish should be picked by immediately and transferred to a fresh water holding area.
Rotenon is available in several forms.
Rotenone powder usually contains 5 percent rotenone, but sometimes, a 4 percent rotenone product is sold. The recommended level of treatment is 0.2 ppm rotenone. This requires 4 g of 5 percent derris powder per m3 of pond water. This does not kill eels. Treatment of 8 g of 5 percent derris powder per m3 of water is required to eliminate eels.
Derris root. Fresh roots are more effective than dried roots which had been stored. Rotenone content appears to be higher in small roots than in larger roots. Rotenone content of the roots also appears to vary with location (Yang, personal communication). The roots should be cut into small pieces and soaked overnight in water. After soaking, the roots are pounded to crush them. The crushed roots are replaced in the water in which they were soaked and squeezed so as much of the rotenone as possible goes into solution. The solution is then added to the pond. Four grams of dry root are required per m3 of pond water.
Diquat, a trade name organic herbicide and copper sulfate (CuSO4) are the only approved herbicide for food fish. Diquat will not kill bluegreen algae; copper sulfate will kill bluegreen algae. Diquat is used at the rate of 2.5 gallons per hectare for the control of filamentous green algae. Diquat liquid should be put into the pond, after dilution to 0.1 strength, by use of a siphon. Copper sulfate is used at the rate of 0.25 ppm for control of bluegreen algae. Copper sulfate at 0.25 ppm is especially useful when wind blows heavy concentrations of bluegreen algae into pond corners. The crystal or snow form of copper sulfate should be broadcasted over a small area of concentrated algae not more than once a week.
Diquat is extremely toxic to human. Rubber gloves should be worn, and the discharge and of siphon hose should always be held underwater. Care should be taken to dispose of diquat containers, and the dilution container should be washed with soap and rinsed thoroughly three times after use.
Illus. 2
- Tang, in 1967, recommended 12 to 15 kilos per hectare of Nicotine5 as a preflood treatment. Tobacco dust should be spread evenly over the pond bottom and raked into the surface soil then flood the pond in 10 cm. This will kill most aquatic organisms. Tobacco dust breaks down into organic fertilizer. The pond should not be stocked for two to three weeks after filling.
= 1,200 kilograms tobacco dust needed per hectare to sterilize pond.
The Fish Control Laboratory at La Crosse, Wisc., and Warm Springs, California, has found malathion at 1 ppm active ingredient to be an effective fish toxication. Malathion is an organophosphate which biodegrades in forty-eight hours at 27°C (80°F). Malathion is sold in several strengths; to find the amount to use first find the total kilograms needed to treat at 1 ppm and divide this number by the percent active ingredient. This will give the kilograms of commercial product needed. Chlorinated hydrocarbons should never be used in food fish ponds. Lindane, (BHC), endrine, DDT, and heptachlor are all residual chemicals. If used in the pond they will remain there for many years. Herbicides of the 2,4-D 2,4,5-T group should never be used in ponds because they are dangerous to the pond manager and to the consumer.
- To identify milkfish seedling from other species, Blanco (1950), gives the following description of bangus fry commonly caught along the sandy shores of the Philippines; “Fry are transparent, needlelike or elongated, measuring 10–13 mm long. The eyes are black in the transparent well-developed head. Mouth is slightly oblique on a narrow and short head. The pectorals are developed. Body is long and narrow with a visible vertebral column of about fifty-one or more vertebrae. The post larval intestine and coiled, parallel to the two-thirds of the vertebral column, and empties into an anus before a narrow and low anal fin near the caudal peduncle. The base of the dorsal fin of soft fin rays is 5.5 times the body length. The homocercal caudal fin is of sixteen caudal rays. Bangus fry of this size when newly caught are devoid of par marks or pigments but when they are about three to four days old in the earthen pots, or jars, they have black pigments of narrow and short spots just above the base of the anal fin. (See Illus. 3).
- Major bangus fry grounds are as follows: Western Coast of Luzon, Mindoro, Eastern Coast of Palawan, Albay, Southern Mindoro (Davao, Cotabato, Lanao and Zamboanga), Western Visayas (Antique and Negros Oriental), Central Visayas (Bohol and Cebu).
are as follows:
Saplad (set fry trap) - this is a stationary bamboo and set at the mouth of rivers, estuarines and tidal creeks. It consists of a v-shaped barricade of crushed bamboo set firmly at the bottom ground facing down stream. At the point of intersection of the crushed bamboo walls is an opening through which the fry are led into the saplad proper a half-hoop fine meshed net of sinamay fiber cloth 1.5 m long and 60 mm wide and held in place by two parallel bamboo poles. The trap is set in shallow water about a meter high.
Sayod or Sarap (Fry Seine) - a seine made of sinamay or fine-meshed cotton netting measuring about 1.5 m wide and 5 m long. Two fishermen, one at each end, drag the seine along the shores.
Sakag (Scissor Net) - it is made of either sinamay or cotton netting and is mounted on a collapsible, triangular frame. It is generally used in wading depths although it may be operated in deeper waters by having it mounted to a banca.
Fry dozer - this is essentially a portable-type “sakag” operated like a push net or scissors net. The v-shaped wings and box end used whole bamboo trunks to keep the gear afloat. Sinamay cloth or fine-meshed netting forms the bottom extending from the crib of a box to wing tips.
Sorting of fry - the fry of certain other species of fishes and of certain crustaceans are generally captured with milkfish fry. Great care is taken to discard the fry of predaceous fishes as these, when stocked in ponds with milkfish fry, are responsible for considerable milkfish losses. The sorting is done by means of a white cup or shell, the unwanted species being discarded in the process of transferring the milkfish fry, a few at a time, from the sorting vessel to the fry container. The sorting vessel is usually a white basin.
In certain parts of the Philippines (Carlatan, San Fernando, La Union), the fry are sorted through wire mesh devices. A wire mesh cylinder, with a bottom but without a top, and whose mesh size is sufficient to permit the milkfish fry to pass through, is placed in the fry sorting basin with some clear water. The assorted fry are then transferred into this cylinder. The milkfish swim out through the wire mesh into the sorting vessel. The fry of the other species cannot do so, owing to their shape or size, so these can be discarded.
Although, at present, all species of fry other than milkfish fry are discarded, shrimp fry of the species Penaeus monodon Fabricus and certain fishes of the Family Siganidae (especially Siganus vermiculatus Cuvier at Valenciennes) are also collected. If these are present in small numbers they are mixed together with the milkfish fry in the fry containers.
Method of counting - collected bangus fry are poured into a big, white basin; a number of fry are scooped by means of a small bowl or clam shell. One man counts the fry in this small bowl or clam shell and when he calls out the number, a corresponding number of pebbles, shells or stones are set apart. A fry are counted and their density is used as the basis of comparison for the separation of the rest of the catch into lots of thousands. The average number of fry, usually in ten jars, is used to determine the total number of consignment.
Illus. 3
- Bangus fry are usually kept in wide-mouthed earthen jars (palayok) of approximately 20-liter capacity. Under ordinary conditions, the quantity of fry stored in a container is dependent more upon available surface areas rather than on the volume of the water medium. Normally, 2,000–2,500 fry can be stored in a jar of 90-liter capacity that is half-filled with water. The first two days of storage has been observed to be most critical period.
- Bangus fry are transported in oxygenated plastic bags. These are placed inside a pandan bag or styrofoam boxes. The plastic bag is 50 cm (20 in. wide, 83 cm (35 in) long and .0075 cm (.003 in.) thick.
In the preparation of fry in plastic bag for transport, the bag is filled to about ¼ its capacity with sea water. Such bag can hold from 6,000– 10,000 fry. The bag is then deflated by pushing the excess bag material down to the water level and after which, oxygen is filled in through a hose to inflate. The bag is then tightly closed with a rubber band and is ready for transport.
The number of fry or fingerlings to be stocked in a pond is dependent on the type and amount of food raised and the carrying capacity of the ponds, and also on the size the fish farmers would want their fish to grow.
The best time for stocking the fry in nurseries is during the colder parts of the day, in the evenings and early mornings. Before the fry are released, it is advisable that the temperature and salinity of the water in the jars and the ponds where they are to be stocked be almost the same. If the difference in temperature and salinity is too great, efforts should be made to slowly bring them closer together, otherwise the stocking should be delayed to avoid undue mortality.
During the stocking, the jars of fry are brought to the nurseries preferably near the gates which are supposed to be the deepest parts of the ponds. Each jar is brought down to the pond and tilted toward one side to allow the pond water to flow gently into the jar. This process may be prolonged depending upon the range of difference of conditions of the jar and the pond water. When the jar is almost filled with water it is slowly raised and at the same time tilted but leaving an air exit at its mouth. In this manner the water with the fry is put in the ponds almost undisturbed and without agitation.
The concept of stocking rate is variously interpreted in different countries. In many places this rate is reckoned simply in number of stock per unit space of the habitat and with due consideration to the age group of such stock. In others, weight of stock per unit space is considered regardless of age groups of such stock. The first practice is convenient and popular and is generally accepted as a matter of course by many fishpond operators.
Stocking rates in the nursery ponds depend on the amount of food and space available for the fish. One hectare of nursery ponds with good growth of lab-lab may be capable of supporting around 300,000 bangus fry, or a rate of 30–50 fry per square meter.
- stocking rate depends on the different kinds of fish food. A hectare of rearing pond with sufficient growth of fish food will have the following stocking rates:
For lumut, the rate is usually from 1,000–1,500 fingerlings per hectare.
For lab-lab, the rate is 1,500–3,000 fingerlings per hectare.
For plankton, the rate of stocking would be from 3,000–5,000 fingerlings per hectare.
Supplemental feeds are foods that are introduced to the pond when the natural food grown is not enough. These can be in the form of rice bran, bakery rejects, filamentous algae or any prepared mixed ingredients.
Bangus in brackishwater fishpond depends on natural food grown in the pond. In the nursery ponds, bangus fingerlings are given supplemental feeding when the natural food present in the pond are consumed, or when there are no available ponds with good algal growth to transfer them into. Supplemental feeding consists usually of rice bran in the morning or afternoon with a total rate of less than 5% of their body weight. The idea is to have just enough energy food and thus fish are stunted and kept indefinitely at that state even after new fry season comes.
In other ponds, such as the transition, formation and rearing ponds, it is the usual practice that natural food are grown in the pond before stocking them with fish. When natural food is almost consumed, the fish are either harvested or transferred to a newly prepared pond which is usually larger than the former.
Some fishpond managers in Manila Bay area, in the province of Cavite, Rizal, Bulacan and Pampanga and in Pangasinan, resort to supplemental feeding when natural food runs out. Filamentous algae, like gulaman dagat (Gracilaria) and “Lumut jusi” Cladophora collected from natural waters or purchased from other fishpond operators, are transported by boat or horse-driven cart to be used as supplemental feed. The filamentous algae are just dumped in the pond. There has also been an old practice in fishponds of Manila Bay area to feed the bangus with bakery rejects (old bread) about a month before harvest. Bangus are given enough food so they get fat bellies before harvest, which commands a higher price.
Commercial feeds have become available which claim to fatten and hasten growth of bangus while at the same time fertilize the fishpond to stimulate the growth of planktons.
After the ponds have been stocked with fish, it is necessary that pond water is kept in good condition so as to minimize the mortality of cultured fish. A fishpond operator should have a tide table in order that he will know the tide prevailing in the area. By knowing the days and height of tide during certain times, one can schedule the activities of the farm.
Since supply of water for brackishwater ponds depends on the tide, it is during spring tide that the freshening of the water is undertaken. Spring tide occurs when the moon is full, or every 28 days. During spring tide when the tide is at the highest (occuring for 4 to 5 days), new seawater can therefore be allowed in pond.
To undertake the freshening of pond water, the sluice gate is first checked. Screens are properly set at both ends of the gates. The screen located inside the pond will prevent escape of bangus when they go against the current as new tide water is allowed in; while the screens located outside the pond will check any suspended debris on the water such as leaves, weeds, branches of the trees, etc. from getting through the gate and clogging other screens.
When the tide is high, the flash boards or slabs are lifted up to allow new water to get in the pond. The first high tide of each spring tide that can get inside the pond only lasts for a few minutes so it will be possible to lift up all the flash boards in order to allow as much water before the tide recedes. When the level of water inside and outside the pond is the same, the flash boards are replaced on the gate.
On the second day, a portion of the pond water, approximately ⅓, is drained about 3 to 4 hours before the tide gets high and is replaced by the same amount when high tide comes. The process is repeated for the duration of spring tide.
Waterpump - Brackishwater fishponds depend on tide for the supply of water. During neap tide, when high tides are usually lower than the water level inside the pond, water can not be put into ponds without the use of pump.
During summer, high air and pond water temperature and strong wind will result in a rapid rate of evaporation causing the salinity to rise. It is therefore necessary to freshen the pond water. If this occurs during neap tide, a pump should be used to freshen the pond.
Pumps have been used in fishponds for the following purposes:
Supply water to the pond when water condition is critical. Types of critical water situations may be either low or high pH, high salinity, high temperature or low oxygen level.
To drain water in ponds the bottom of which is below low tide level.
The most common pumps used in fishponds are the centrifugal and propeller-type water pumps. With the same engine power, a propeller-type is more effective as it can pump a greater amount of water because it pushes water from the source rather than using suction to pick up water from the source.
Temperature directly affects the fish and influences other factors such as salinity and dissolved oxygen.
Temperature in a pond is lower at night than during the day. Bangus production is not affected very much by the low temperature ranges which occur in the Philippines. Temperature of pond especially during hot summer goes as high as 35°C. This can cause distress to fish as the rate of body metabolism is increased. To minimize rise of temperature in fishponds it is necessary to maintain the water level as high as possible. Providing a canal running across the pond is useful to provide a refuge for fish during hot days. Pumping water will also help in lowering the pond water temperature, provided the water pumped in is lower in temperature than the pond water.
Low dissolved oxygen is a reason for changing water (see water chemistry).
pH is the potential of hydrogen expressed as of hydrogen ion concentration. This is the measure of alkalinity or acidity of a solution. pH of pond water can be determined with the use of pH paper or electronic instrument.
The pH value of pond water good for growing bangus should be slightly alkaline, ranging from 7.5 to 9.0. The pH of water of nearly constructed fishpond is usually low or acidic due to presence of decaying roots and other materials in the pond. This should be changed by liming. (See section 2.2.6.5.)
The pH of brackishwater fishponds does not usually get high. More often they drop to low level due to certain factors such as presence of decomposing organic material or overstocking of a pond. This has a direct effect on fish and the algae growing in pond. Low pH can sometimes be remedied by constant refreshing of pond water.
Bangus is a euryhaline fish so it can tolerate a wide range of salinity from zero to 60 ppt, but an abrupt change of salinity can cause distress or even death to the fish. A range from 10 to 35 ppt is ideal to attain a good growth.
A fishpond operator can have a close watch of the salinity of pond with the use of hydrometer or a refractometer. A hydrometer is simple and inexpensive; salinity is determined by collecting a small amount of pond water where the hydrometer is floated. The reading of salinity is at the water level where the hydrometer is submerged. A refractometer is an expensive device but very useful. With a drop of pond water placed on the refractometer, the salinity can be determined thru direct reading.
Salinity can drop easily to almost fresh water during rainy days. It is therefore necessary to allow as much as tidal water to the pond as possible when rain will be expected. This will minimize dilution or abrupt lowering of salinity when heavy rain falls. Usually rain water will stay on the top level of the pond so excess water should be overflowed over the gate boards.
Freshening or current method (pasuba) - The bangus have a tendency to swim against the current. This tendency of the fish is harnessed in catching them. The steps to be done under this method are as follows:
The rearing pond to be harvested is partially drained of its water during low tide and then letting in new tidal water in the next incoming high tide. The fish then swim against the current created by the inflowing water passing through the opened gate into the catching pond where they are confined.
The gate is closed as soon as the catching pond is filled with fish. This technique prevents rapid spoilage during transporting and marketing.
Fish are harvested by seining or scooping after confinement. Harvesting by use of the freshening or current method may fail if (i) reduction of water depth in the pond is insufficient, (ii) ponds are too deep to drain because of tide, (iii) fish are not hungry, (iv) the tide is receding. This method is the typical procedure, popularly used by majority of fishfarmers, for the following reasons:
It is easier, faster and takes less manpower to do the job.
Fish retains its freshness.
The fish are comparatively cleaner
The food, if there is any, remains on the pond bottom.
95% of the fish stock can be harvested by “pasuba” method.
Draining - The rearing ponds should be drained totally during low tide at night time. When fish are confined in the catching pond, they are scooped or seined for market. This method enables one to remove all undesirable fishes in the pond. The objection to this method is it lowers the quality of the harvest because of the mud that adheres to the fish which is difficult to remove.
Seining - A seine is used if partial harvest of the stock is required.
Gill Netting - Gill nets are dragged across the pond rather than set as practiced in wild fish harvest. Gill-netted fish have a low market price because fish are bruised and some scales are removed from the fish.
Bamboo Screen - The bamboo screens are joined together by bamboo splits, erected on one side of the pond and dragged towards the other side, where a catching chamber is constructed to gather the fish or by confinement of the fish which may be done by encircling.
Use of nets and bamboo screens - This method is used only in special cases, such as:
For limited household consumption
For small-scale selling
For friends or visitors.
Gill netting and bamboo screen method muddy the pond bottom.
Bamboo screen trap - The trap is set in any place of the water supply canal which has a gentle flowing current. The catching chamber is always in contact with the incoming water current. The way to entrance chamber and the catching chamber should be equidistant to the leader. Operation is done during nighttime. If possible, the catching should be provided with “lampara” light. The catching of the shrimps is by scooping with a dip net in early morning to ensure freshness.
“Aguila” trap - The trap can be operated in a place where there is gentle flow of water during nighttime. The setting should be made in deeper portion of the pond to catch “sugpo” or “hipong puti”.
“Lumut” trap - The net is attached to a frame which is then attached also to the gate. The operation should be done during low tide when letting out water from the pond. A swift current forces the shrimps to enter the net.
A fish' natural environment is water. When fish are removed from water they are subjected to stress. Low oxygen, pollution, sudden pH or temperature change also cause stress to fish. Fishery workers try to handle fish so that the least possible stress occurs.
Fish that have undergone stress are more likely to have disease. In some cases, as in large volumes of water, it is not economical to treat the fish for disease. Seedling transfer is a situation that will allow for easy and economical disease treatment. All seedlings should be transferred in combiotic6 dilution of fifteen parts per million. If losses still occur, one or more other treatments should be tried. The safest course is to try a few seedlings at a time with the following treatments:
Dylox - 1 ppm (Dipterex, Masoten Chlorotos)
Malachite green - 0.25 ppm
Formaldehyde - 1:12,000
Remember that all chemicals are dangerous if not handled or stored properly. Keep them away from children.
Many human diseases, including plague, tuberculosis, roundworms, cholera and typhoid are carried by brackishwater fish.
6 Combiotic is 50% terramycin, 50% penicillin
Materials
Gram Balance
1 10cc syringe (plastic)
1 2cc syringe (plastic)
Dylox - 80% wettable powder
Formaldehyde - 40%
Combiotic liquid
Malachite green - zinc free, reagent grade
1 balance 1g to 100g
Methods:
Dylox - Measure volume of water to be used in seedling transfer. Calculate weight to be used to treat at one part per million (1 mg per liter). The easier way to make this dilution is to weigh one gram of dylox into one liter of water to make a stock solution.
Use one milliliter (1 ml) of stock solution of each liter of water to be used for fry transfer. Test dilution with a few seedlings.
Malachite green - Measure one gram of malachite green into one liter of water. Use 0.25 ml of stock solution per liter of water to be used for seedling transfer. Test dilution with a few seedlings.
Formaldehyde - Measure 0.8 ml of 40% formaldehyde into water to be used for transferring seedlings. Test dilution with a few seedlings.
Combiotic - Measure 1 ml of combiotic into one liter of water. Use 15 ml of stock solution per liter of water to be used for transferring seedlings. Test dilution with a few seedlings.
Most fish disease organisms have not been identified in Philippine brackishwater fishponds. The above treatments are suggestions based on experience in other countries.
The production and maintenance of appreciable level of natural fish food in pond is a serious problem confronting the fish farmers. Predetermining the size of fish population for a particular standing crop of natural fish food is difficult, as a result, the manager may end up with undersized fish. In such situation, the fish are either moved to another pond, or supplementary feed is given to the fish. One type of supplement is “lumut” or lab-lab introduced into the pond. Algae is grown separately in a pond compartment, usually the nursery pond when not in use for the growing of fry, and transferred to the rearing pond.
A feed pond is a pond compartment used primarily for the production of desirable algae to supplement the fish food in the rearing or transition pond.
A recent innovation in bangus fishpond management is a feed pond as a permanent structure in a fishpond project. Technology and economics of this method has not been fully established although some fish farmers are already making progress along this line.
Procedure:
A feed pond is constructed between two rearing ponds, the size varying in proportion with the pond it supports. One hectare of feed pond in support of five hectares of rearing pond is typical.
Feed ponds are developed to meet the requirements for lab-lab production. Pond preparation is for lab-lab production. Unlike a pond where fish are stocked, a feed pond can be heavily fertilized with organic fertilizer to maximize the production of lab-lab without the worry of danger to fish.
The rearing pond is also prepared for lab-lab production. Since fish food is not sufficient to meet the requirement of fish stock in this pond, lab-lab from the feed pond is transferred by raising the water level in the feed pond and by gravity, the lab-lab is carried into the rearing pond through a pipe connection.
Excess lab-lab produced in feed pond can be dried and preserved for future use.
