Fish stock manipulation techniques in aquaculture for higher yield

Mrinal Kanti Datta
Contd from prev issue
The process is most popular in Assam and Tripura.
 The stocking density can reach as high as 30,000 fingerlings/ha. Periodical harvesting of large sized fishes is followed by restocking of half to the same number of seeds in the same pond. The system needs special care for water quality and oxygen management.
This is a scheduled monthly activity of grading the fish stock into different size groups to reduce the adverse effect of uneven growth and association of “size of hierarchies” within the fish population. Smaller fish are harvested later when they reach the desired size and weight.
An attempt was made to modify the stock manipulation technique as practiced in Taiwan to suit Philippine conditions. Three 1500 m2 ponds were each stocked with three size groups of milkfish, viz., half grown, 1500/ha; post-fingerling, 15000/ha; and fry, 3000/ha. One month after stocking, another batch of fingerlings was added to the ponds at the rate of 15000/ha. This was followed by another batch of fingerlings at a stocking rate of 15000/ha. Two months after the initial stocking, 50% of the marketable size (stocked as half grown) were harvested. The other 50% was harvested one month later. In the fourth month after the initial stocking, 50% of the marketable size fish (stocked as the first batch of post-fingerlings) was harvested. One month later, the remaining 50% was harvested. A monthly harvest was thereafter programmed until the last batch of fingerlings was harvested. The results showed a significant difference in milkfish production between stock manipulation ponds and non-stock manipulation ponds. Production in the former ranged from 734 to 961 kg/ha, while in the latter, it was from 613 to 702 kg/ha, indicating that stock manipulation can be a positive technique for yield enhancement.
The technique of stock manipulation is a boon for the small and marginal farmers who have small water bodies, may be seasonal in nature and cannot invest huge amounts in fish culture for a longer period. Without much increase in input cost and considering the local demand, this technique can enhance the fish yield and profit.
The writer is from College of Fisheries, Central Agricultural University, Lembucherra, Tripura, 799210 For further details contact: -Public Relations& Media Management Cell, CAU, Imphal. Email: [email protected]