Fish stock manipulation techniques in aquaculture for higher yield

Mrinal Kanti Datta
Contd from previous issue
Continuous harvesting and stocking method not only gives the farmers a constant income and a higher average price, but also thins out the stock and thus improving the growing conditions for the younger stock remaining in the ponds. This methodology can enhance total yield significantly.
Stocking of fish of one size in one pond. When more space is needed, transferring them to a larger adjacent pond. The smaller ponds are prepared for using then for rearing of the succeeding batches. The number of harvests increases from 1-2 times under this type of operation.
Culture of two species in the same pond in different seasons, taking the advantage of different thermal requirements of the two species. This method may increase the income more than 100 percent. Crops may be for monsoon the post monsoon with carp and during winter with cat fishes as well as air breathing fishes.
· mono-specific
· multi-size
· medium-water-depth method
This particular method calls for pond bottom drying and fertilizing with organic and chemical fertilizer then watering with 10 to 15 cm of water and slowly deepening this level to 75-100 cm at which time planktonic food would be well established. Stock of fish is then introduced in two to four sizes. Usually the bigger ones are the hold-overs from previous crop.
· About 12,000 nos./ha of (6-8 inches) 15-20 cm or 8-12 fish to a kg
· About 14,000 nos./ha of (4-5 inches) 10-13 cm or 40-50 fish to a kg
· About 18,000 nos./ha of (2-3 inches) 5-8 cm or 150 fish to a kg
Subsequently the pond water is gradually increased to 100 to 150 cm as the fish grows.
The above numbers may vary depending on the carrying capacity of the pond as observed by the farmers. After 60 to 90 days, the big ones are harvested either by cast or drag net. Another batch of small size seeds are again introduced. Every 30 to 50 days, the larger fish are harvested until it is decided to stop the culture and a final harvest is made. The remainder smaller fish are stocked in holding ponds for the next culture period.
(To be contd)