The hatching techniques of carp eggs have undergone a lot of changes to get better hatching and survival from the earthen hatchery pits and cement hatchery pits at spawn collection centres. Use of double hatching hapas is being replaced by running water systems, with or without temperature control. The water hardened eggs are measured, their number calculated and a sample is examined to find out percentage of fertilization.
Microscopic view of a fish egg
Under field conditions, the eggs are kept in double-walled hapas, outer wall is made of close-meshed cotton or nylon and inner wall is made of thin round-meshed mosquito net. The inner hapa is smaller, leaving gaps of 15 cm on all sides and also at bottom between the inner and outer hapa. In an outer hapa of the size 2 m × 1 m × 1 m and a suitable sized inner hapa a total number of 50,000 - 100,000 eggs can be kept for hatching depending upon fertilization. The eggs are distributed in the inner hatching hapa uniformly. The hatching time is 16–18 hours in the case of Indian major carps and nearly two hours more in silver carp and grass carp at optimum water temperature range of 26–31°C. The hatchlings pass through the inner hapa to outer hapa and inner hapa is removed. Inner hapa with wooden frame is found quite convenient for uniform distribution of developing eggs. Floating hapas are also used for hatching purpose. For best results in the hapa system of rearing, the breeding as well as hatching hapas should be installed in running water. Apart from the hapa method, these fertilized eggs can be hatched out using Indian jar hatchery system (or) Chinese hatchery system.
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