Spawners of P. japonicus, P. aztecus, P. duo-rarum and P. setiferus can be collected in largenumbers, whereas spawners of species like P.monodon are more difficult to obtain. There-fore, maturation of captive stock of wild-caught or pond-reared adults is necessary for large-scale hatchery production of adequate numbers of larvae of these species.
Some species, like P. merguiensis and P. japonicus, mature, mate and spawn freelyin response to controlled environmental conditions. Unilateral eye-stalk ablation is adopted for species which other-wise do not mature in captivity, like P. aztecus,
P. duorarum, P. monodon and P. orientalis. Evenfor species that would mature without such treatment, ablation helps speedy maturation and better spawning rates. By eye-stalk ablation it is possible to reduce the interval between spawnings to 3–15 days, from the normal interval of 10–67 days.
The technique of ablation or extirpation involves the removal of either eye and the partial or total removal of the eye stalk by cutting with surgical scissors, cautery (using a soldering iron or clamps or by electrocautery), ligation, squeezing or crushing the eye stalk tissue, or manual pinching. It is important to prevent excessive loss of eye fluids and infection. The interval between ablation and the onset of maturation and subsequent spawning varies from three days to more than two months, depending on a number of factors including the age of the shrimp and the stage of the moulting cycle. It is considered best to undertake ablation during the intermoult, for
maturation to follow in less than a week. Ablation during the premoult period can lead to immediate moulting and a prolonged latency period. Maturation and viability of eggs seem to depend on the water quality (salinity, temperature and pH), light intensity and nutrition. Spawning stock is given high-quality feed, preferably natural foodstuffs like polychaete worms, squids, mussels, clams or cockle meat, at the rate of about 10 per cent of the biomass. A continuous flow of water is maintained in the maturation tanks and a daily exchange of 60–70 per cent of the water is recommended.
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