1. Nursery Pond Management
The nursery pond will be stocked with fry three times a year, in April, May and September (Appendix 2). Preparation of the pond includes draining and drying to eliminate pests and predators, mineralize the soil and provide a more stable medium for lab-lab to get attached. Organic fertilizers will be mixed with the top layer of the soil while it is still wet. Addition of urea to cow dung or compost in a proportion of 3:100 by weight, dry basis, before working the mixture with the soil will help to hasten decomposition of the organic matter. A second application of urea and triple-superphosphate at 45 kg/ha each and about 60 kg of molasses will start lab-lab immediately after water is allowed.
Measures will be taken to prevent entry of predatory fishes of their larva when water is first allowed.
As long as the water is clear and salinity does not go beyond 40 ppt, freshening of the pond waters is not necessary before the fry are released. Stocking will be done via a well prepared acclimatization tank 1 “baby box” provided with overhead and side shading and water that has been toned down to around 20 ppt, roughly ⅔ the salinity of normal sea water. The fry will be released during the cool period of the day, preferably late evening after careful acclimatization (temperature and salinity) to conditions in the baby box. Inside the tank, usually 12 hours after stocking, salinity is gradually raised until it approximates that of the saltier water in the main pond. This is done by making a small cut on one dike and installing a fine screen across the cut. This will allow diffusion of salt into the tank, yet prevent the fry from going out prematurely. The fry are ready for release as soon as many are seen converging and swimming against the screen. Acclimatization usually takes from 24 to 48 hours.
If there is threat of rains, the dikes of the tank are draped with clean plastic sheets to prevent muddy run-offs from entering.
The fish should be transferred to a clean pond with ample food after three or four weeks. It should always be a rule that fingerlings should never stay in the nursery pond for a continuous stretch of 30 days; however in the event that compartments are ready, at the end of this period the fish may be temporarily fed with lab-lab from other sources or stale wheat flour. Very fine rice bran may be used if no other feeds are available.
1 About 1 m2 for every 3 000–5 000 fry.
The early fingerlings are transferred to the fingerlings/holding pond. It should be well prepared, free of predators and with plenty of natural food. The same 30-day rule on length of stay should also be followed here.
When not in use, the holding pond may accomodate marketable fish temporarily while the fish farmer is waiting for better prices.
2. Rearing Pond Management
2.1 First crop season, mid-May to mid-September.
| Mid-May | - | Pond will be drained. Soil will be dried until it is hard enough to support an average man without sinking more than 2 cm. |
| - | Sea water will be allowed up to a depth of about 5 to 10 cm. Four hundred kg of tobacoo dust, 80 kg of molasses and 45 kg each of urea and triple-superphosphate will be applied. To save labour, tobacco dust, urea and triple- superphosphate will be broadcast over the dry pond bed immediately before water is allowed. Molasses may be diluted very thinly and poured slowly from the sluice as water comes in. | |
| - | Depth of water will be increased gradually up to 25 cm after the snails and all other pests and predators are exterminated. By this time lab-lab will have developed and covered almost all of the pond bottom. When it is from 1.5 to 3 mm thick, the pond is ready for stocking. | |
| Early June | - | After toxicity tests show that the water is safe, the pond will be stocked with 1 500 fingerlings 10–15 g in weight. |
| - | Two weeks later, 1 000 more of the same size will be added. | |
| Mid-August | - | The first stock will be harvested and a new batch of 1 750 fingerlings of 30–40 g weight will be released. |
| Mid-September | - | All the remaining big fish will be harvested and the post fingerlings transferred to the holding pond for stocking during the second crop season. |
| Note: | Weekly fertilization with 8 kg urea and 10 kg triple-superphosphate will start two weeks after initial stocking and will continue for the next 5 to 7 weeks. | |
| Pond waters will be freshened if salinity exceeds 40 ppt. Freshening is done by drawing out part of the water and replacing it with new tide water up to its former maximum level. Water will be freshened only just before fertilization. | ||
| To control chironomid larvae, Basudin 101 will be applied at one g per m3 of pond water. |
1 Basudin 10 should not be applied 3 weeks before harvest of marketable fish.
2.2 Second Crop Season, Mid-September to Mid-January
| Mid-September | - | Pond will be drained. As soon as the bottom is exposed, 2 000 kg of cow dung, compost or similar organic fertilizers will be broadcast over the soil. |
| - | Bottom will be dried sufficiently as in the first crop season. | |
| - | Sea water will be allowed, molasses, urea and triple-superphosphate will be applied in the same quantity and manner as in the first crop season. As soon as lab-lab develops, water will be increased gradually to a depth of 25 cm. | |
| Early October | - | Pond will be stocked with 1 500 post fingerling hold-overs from the first crop season. Another 1 000 early fingerlings 1–2 g will be added. |
| Early December | - | Big size stock will be harvested and replaced with 1 750 fingerlings, 10–15 g. |
| Mid-January | - | All marketable fish will be harvested. Remaining post fingerlings will be transferred to holding pond. |
| Note: | Fertilization and freshening will be the same as in the first crop season. During the rainy season, however, fertilizers will be applied only on, sunny days. For freshening during the rainy periods, twice the amount of rain water already fallen will be let out and replaced with tide water up to the original depth before the rains fell. To control chironomid larvae, Basudin 10 will be applied at one g per m3 of pond water. Fish will be harvested only 3 weeks after the last application. |
2.3 Third Crop Season, Mid-January to Mid-May
| Mid-January | - | Pond will be drained and soil exposed for two or three days. Twenty cm of tide water will be allowed and filamentous green algae (Chaetomorpha spp. Cladophora spp. or Enteromorpha spp. will be induced to grow. If necessary, the pond will be seeded with very young algal stock. As soon as the algae takes hold, 14 kg of urea and 7 kg of triple-superphosphate will be applied. Three hundred kg of cowdung may be added if available. |
| - | Seven kg of urea and 3.5 kg of triple-superphosphate will be broadcast weekly for the next three weeks or until the algae covers about 75 percent of the pond area and estimated production is at least 1.2 kg wet weight per m2. | |
| Mid-February | - | Pond depth will be raised gradually to 30 cm as algae grows. Wave breaks will be set to prevent the algae from getting torn loose due to heavy winds. To provide this, small branches or twigs will be set on lines perpendicular to the wind direction at 10 to 20 intervals. |
| - | Pond will be stocked with all post fingerlings, at least no less than 1 500, held over from the second crop season. | |
| - | After stocking, pond will be fertilized with 10 kg urea and 12.5 kg triple- superphosphate weekly for the next two or three weeks. | |
| March | - | Regular fertilization will continue with 10 kg urea and 15 kg triple- superphosphate per week during the whole month. |
| Mid-May | - | All fish will be harvested. |
| Note: | If excessive rainfall cause the algae to sink to the bottom and remain there for two or three days, depth will be reduced to about 20 cm and replaced with new tide water. | |
| In case Ruppia spp. or other higher aquatic vegetation becomes established before the fish attain marketable size, pond will be drained, stock transferred to the holding pond and the weeds dried under the sun for three or four days. As soon as the plants wither and become white water will be allowed to its former depth and the fish returned to the pond. Fertilization will continue as for filamentous green algae. |
For newly excavated ponds, it may take time before favourable response to physical and fertilizer treatment for lab-lab culture will be seen. Yield for the first year may not come up to expectations unless special efforts are made to improve soil conditions and fertility.
The above programme is based on observations on climatic, soil and tidal conditions in Jepara, results of field tests conducted at the Project's ponds, Expert's experience and observations under similar conditions in the Philippines and studies of other workers along the same lines. The techniques may be modified to suit different situations.
A schematic diagram of stocking and stock manipulation in accordance with the management programme as described is shown in Appendix 2.
