Fish stock manipulation techniques in aquachulture for higher yield

Mrinal Kanti Datta
Economic fish production through mono and polyculture system is dependent upon various factors, such as pond preparation, control of weeds, control of predatory animals, liming, proper stocking, monitoring of physio-chemical parameters, use of manure, supplementary feeding, netting, harvesting, etc. Important cultivable species are carps i.e., Rohu, Catla, Mrigal, Grass Carp, Silver Carp, Common Carp. Rohu, Catla and Mrigal are called Major Carps. Silver Carp, Grass Carp and Common Carp are called exotic Carp. Other species in culture are in Kalabasu, Pangus, Silver barb, Kai, Magur, Singi, Moka etc. These fishes are of high economic importance and are largely used for culture.
Growth of fish also depends upon appropriate stocking and stock manipulation. Proper stocking means maintaining scientific proportion of different types of fishes in ponds. Ponds can support either a large number of very small fishes or small number of large fishes. Though growth of fish in ponds with thin stocking may b very satisfactory, but it is not economical. Total fish population that a given pond can support depends on its carrying capacity in terms of food contained in the body of water or the supplementary food that can be supplied.
Hence manipulating stocking density, sizes etc. may be a tool for higher fish yield and the technique is called fish stock manipulation.
Hence stocking rate of fish pond in aquaculture can be increased by different kinds of stocking systems such as:
· Multiple sizes stocking
· Same size stocking in a system of ponds
· Double cropping
· Sequential harvesting
This may be defined as stocking of the same species in different sizes to make more efficient use of water space. If suitable density of fry is stocked at the beginning, the rearing pond will be overcrowded when fry reach adult size. Growth will be retarded with low survival. The carrying capacity of pond in different age group of fishes is greater from same age group. Multiple sizes stocking requires periodical harvesting of the largest fishes when they reach marketable sizes. After the stock is thinned out smaller fishes are added.
(To be contd)