1.1.2 Pond preparation
A wellprepared pond is important as predators and competitors can endanger the stocked fry.
Some farmers still practice very crude farming techniques of drying the pond bottom and immediately filling with water and stocking fry directly for nursing. Feeding is entirely dependent on supplementary feed such as chopped or grounded trash fish and is done twice daily in the morning (1800 hours) and afternoon (1700 hours). In this method, the survival rate and growth rate are low.
To enhance production, the following improved pond preparation techniques are done: The nursery pond must be drained and dried until the bottom soil cracks to release toxic gases, oxidize mineralized nutrients, eradicate some pests and predators. In cases where the pond cannot be completely drained, derris root (rotinone) may be applied at the rate of 20 kg/ha toeradicate unwanted species. Derris root is prepared by cutting them into small pieces, crushing and soaking in water overnight. Only the solution is applied to the pond. If derris root is not available, a mixture of 50 kg/ha of ammonium sulfate (21-0-0) with lime at a ratio of 1:50 will be sufficient to weed out unwanted species. The mixture is applied to the portions of pond with water. The use of any chemicals or inorganic pesticides is not recommended because the residual effect remains for many years and can reduce the pond production. If pond soil is acidic, the pond bottom should be neutralized with lime before letting the water in.
Production techniques of juvenile in nursery ponds have been improved recently at Satul Fishery Station, Thailand. The improved technique is based on the live food production in the pond supplemented with chopped or grounded trash fish. After neutralizing pond bottom by liming, organic fertilizer (chicken manure) is applied at the rate of 500 kg/ha. Then water depth is gradually increased for the propagation of natural food. Two to three weeks prior to stocking, newly-hatched Artemia nauplii are inoculated into the pond (1 kg of dry cyst/ha). Artemia will utilize the natural food as feed for growth and will reach adult stage within 10–14 days. The fry are immediately stocked at the rate of 20–50 individual per square meter.
Another approach to the improved technique is to stock Artemia nauplii in the separate pond and grow them into adult. Adults could be harvested daily to feed the fry.