I. Pond Preparation
Prepare the ponds a month before stocking fish in the following manner:
Draining and drying. Drain and dry the pond completely. Dry for about a week or more, depending upon the weather, until the bottom cracks or harden sufficiently to support a man on his feet without sinking more than 1 cm.
Make sure the pond soil is dried every time the pond is harvested. Periodic drying stabilize soil colloids and oxidizes organic matters that encourage the growth of natural fish foods. Draining and drying eradicate competitor fishes and predators, and kill disease-causing organisms.
Cultivation of pond bottom. Till or cultivate the pond bottom as soon as it is drained. Do this by stirring or cultivating with a shovel or a rake for small ponds. For large ponds, use a rotavator.
Cultivation makes sub-surface nutrients available at the surface for the growth of fish food in the pond, eradicate burrowing predators like mudfish and eliminate undesirable pond weeds like “aragan.”
Leveling. Level the pond bottom after this is cultivated. Leveling makes the pond bottom slope gradually from its farthest end down towards the drainage structures – the deepest portion of the pond.
Repairing gates and screens. Check all gates and pipes for broken slabs and other parts. Repair screens to prevent predators and pests from entering the pond system. Clean to remove debris which may cause clogging.
Repairing dikes. Check all dikes for leakages and seepages. All dikes must be water-tight. Put a puddle trench excavated about 30 cm wide and 50 cm deep or more along the dike. Build this at the center of dike towards one side, or dig two puddle trenches at both sides of puddled trench long enough to cover the entire seepage and sufficiently deep to go beyond the general level of the pond floor. Fill the trench with new mud or soil. Allow the soil to settle well to give a firm line of earth.
Pests, Competition and Predator Control
Fish production in ponds is commonly affected by some pests and predators. Predators are organisms which prey on the cultured fish. Animals that compete for food or space are called competitors.
a. Piscivorous or predatory fish and other competitors
- Catfish (hito), mudfish (dalag) and gurami may enter ponds during floods or when accidentally stocked with the cultured fish. These predators devour fry and fingerlings during or after stocking. To avoid them, drain the pond totally after harvest or before stocking.
- Mudfish which tends to burrow into the mud, can be totally eliminated by using tobacco dust at the rate of 500 kg/ha. Screen water gates and outlets properly to prevent entry of unwanted fishes. Check fingerlings properly for any possible contamination by predatory fish prior to stocking. Competitors are associated with predators. Both compete with the stocked fish for space and food.
- Herons, kingfishers and other birds must be prevented from frequenting the ponds. They devour fish and fingerlings and are also carriers of parasites. Ponds constructed without shallow areas are not attractive to birds.
- Snakes prey on small fish. Always keep banks and dikes clean to prevent snakes from harboring in the ponds.
- Frogs eat fry and fingerlings. Tadpoles also compete with the fish for space and oxygen. Frogs are seldom found in well-fertilized and well-stocked ponds. Their population can be controlled by removing their egg sacks from the pond water.
- Soil acidity limits the production of natural fish food by decreasing the amount of plant nutrients and, in some extreme cases, kill fish. In cases where soil pH is below 7.0, it is important to control acidity to ensure high fish production.
- Analyze pond soil at least once a year to determine its exact pH value. Soil analysis is especially recommended for newly constructed fishponds as basis for proper soil conditioning. Refer to Appendix D for proper collection of soil sample.
Methods of controlling and correcting acidity
- Leaching. Wash or flush the pond bottom to reduce acidity. This process is effective in slightly acidic soil.
- Liming. Apply lime in fishponds primarily as a soil conditioner. Liming corrects soil acidity, promotes the release of soil nutrients, precipitates suspended materials which hamper light penetration and reduces incidence of fish diseases.
Agricultural lime (CaCO3) is the most common time used in fishponds. Unslaked lime or quicklime (CaO) and slaked lime (Ca COH)2 or hydrated lime may also be applied. These are available on arrangement with agricultural input dealers.
Procedure in Lime Application
Broadcast or spread the needed lime over the drained but moist pond bottom. Mix the lime, thoroughly with the soil to attain maximum effectiveness. Allow one week to lapse before applying phosphate fertilizer.
Applying fertilizer in ponds to supply the nutrients needed for plant growth is a fundamental part of fishpond management. Fish production per unit area can be increased as much as five-fold by proper application of fertilizer. Fertilizers are classified into two groups:
Organic Fertilizer. The nutrients and organic matter content of manure increase the water holding capacity of the soil, decrease the rate of evaporation and increase enzymatic activity, all of which increase fertility and yield. Animal manures contain the major nutrient components such as nitrogen (N), phosphorous (P), and potassium (K), in addition to such trace elements as calcium (Ca), copper Cu) iron (Fe) and magnesium (Mg). Phosphorous comes mainly from feces except from swine manure which has more nitrogen and potassium. Animals fed with roughage ration excrete more potassium than those fed with high concentrate rations.
The chemical composition of manure also varies depending upon the animals, nature and amount of manure and the handling and storage of the manure before use. The most common organic fertilizer used in fishponds are chicken dung, cattle manure and swine manure. Chicken manure may be utilized as fish feeds and at the same time helps create a soft mulch bottom to make a habitat for other food organisms. Compost, rice bran, and sewage may also be used.
Inorganic Fertilizer. These are chemical fertilizers containing concentrated amount of at least one of the three major plant nutrients: nitrogen, phosphorous, and potassium. The common fertilizers used in fishponds are Super phosphate (0-20-0), Monoammonium phosphate (16-20-0), and Diammonium phosphate (18-45-0).
Techniques in Fertilizer Application
- Apply animal manure in heaps of 20-50 kg at several locations in the pond to prevent excessive absorption of dissolved oxygen during decomposition.
- Apply inorganic fertilizers in fishponds using the platform method. The platform is a table-like structure about 75 sq m positioned with its surface horizontal beneath the water surface. Bamboos are excellent for constructing platforms.
- Position the platform 15-20 cm below the water surface. Do not place this in corner, or in areas shielded from the wind. The platform saves approximately 20-40% of the required amount of fertilizer.
- Put the inorganic fertilizers by placing them in gunny sacks suspended in the water to enable this fertilizer to dissolve gradually thus, providing a continuous supply of nutrients for the plankton.
- Plankton is a collective term for all the small suspended organisms that passively drift and float in the water. Most planktonic organisms are microscopic and consist of phytoplankton (very small plants) and zooplankton (very small animals).
- Tilapia consumes plankton as food. Plankton is responsible for producing greater fish weight than any other type of natural food raised in ponds.
Procedure in Growing Plankton:
- Drain the water completely for a minimum of 24 hours.
- Fill the pond with water to an average depth of at least 20-40 cm. Increase water level to 80 cm after the first week.
- Apply 22 kg/ha of 18-45-0 or kg of 16-20-0 per hectare on the platform.
- In case of organic fertilizer (chicken, hog, cow or carabao manure), apply 1.5-2 tons per hectare of pond per month.
- Stock the pond after one week.
- Repeat the same fertilizer treatment after one week and then as often as necessary to keep visibility to 30-40 cm.
II. Stocking of Fingerlings
Sources of Fingerlings
High quality fingerlings ensure better profit in tilapia culture. Inferior tilapia fingerlings grow slowly and may not reach the desired marketable size of 85-100 grams in 4-5 months culture period. Fish-farmers should secure their initial stocks from reliable sources.
Time and Method of Stocking
The best time for stocking fingerlings in the pond is late afternoon or early morning. Before the fingerlings are released, ensure even temperature between the water in the plastic bags and the pond where these are to be stocked. If the difference in the temperature is more than 3Â°C, introduce water gradually from the pond to the plastic bags until the temperature is almost the same.
To stock, bring the plastic bag of fingerlings to the pond preferably near the gate which is supposed to be the deepest part of the pond. Bring down each bag to the pond and tilt towards one side to allow the pond water to flow gently into the bag. Allow the fish to swim out of the container voluntarily. One oxygenated plastic bag contains 300 fingerlings.
Fish Stocking Density
Fish stocking ratio is one of the several factors that affects fish growth. At low stocking density, the amount of natural food in the pond is higher for each individual fish and the excess food is not utilized. As long as other factors are not limiting, the growth of fish is not utilized. As long as other factors are not limiting, the growth of fish will be better. The maximum physiological growth of tilapia is attained at low stocking density.
A one-hectare pond with plankton can accommodate 10,000 to 20,000 fingerlings of nile tilapia measuring 3-4 cm. Supplemental feeding is necessary to have better produce.
The stocking density influence the inputs needed and yield of the fishpond. Failure to select the most appropriate stocking density results in poor growth and low market value of fish. Select the proper stocking density in ponds based on the following factors:
Market demand. Market size preference varies depending on the place. In many barangays in Region 2, small fish (less than 100 g) are highly saleable. In commercial fishpond operations that require middlemen in marketing, large fish commands a higher price than small ones.
Productivity of the pond. Old ponds are more fertile than newly constructed ones. The mud containing organic nutrients can readily be used in the growth and support of plankton that serve as the natural fish food.
Quality and quantity of feeds used. The stocking density of a pond can be increased when supplementary feeds are given to the fish. Supplementary diet with high protein content is best in ponds with very high fish population. For example, rice bran mixed with fish meal will produce better feeds than rice bran alone.
Quality and quantity of fertilizer and methods of application. Animal manures with higher phosphorous and nitrogen content are best for intensive fish production. Chicken dung is widely used because it ensures much higher yield than cow or carabao manure. The capacity of the pond to accommodate fish can be further increased when inorganic fertilizer like 16-20-0 is added with the manure into the pond.
Fish-farmer’s resources. Low stocking density may be recommended for fish farmers of the low income group. The recommended stocking ratio must conform with the ability of the fish farmer to supply the needed inputs.
The ideal stocking density of nursery pond is 30-100 fry per square meter. For rearing production pond, stock 10,000 to 20,000 fingerlings per ha or 1-2 fingerlings per square meter.
source: STII and PCARRD