What is Composite Fish Culture?
In order to obtain high production per hector of water body, fast growing compatible species of fish of different feeding habits are stocked together in the same pond so that all its ecological niches are occupied by fishes. This system of pond management is called mixed fish farming or composite fish culture. It is also known as polyculture.
Why preferred the Composite Fish Culture?
A single species of carp culture in a pond is known as mono-culture and previously this mono-culture was the normal practice in many of the countries. Hence there was a small production of 300-600 kg of fishes per hectare of water in a pond. Subsequently there is a great change in the process of carp culture. Instead of single species, more than one species of major carps have been selected for rearing and culture in the same pond. They are living in the different water levels as well as they have different feeding habits. This process of rearing of fishes is known as composite fish culture. Recently three exotic carps such as silver carp, grass carp and common carp along with the three Indian major carps are selected for composite carp culture in the Asian countries. Thus the composite fish culture or composite mixed culture of six species is now introduced in the same pond. They are to be reared scientifically so that there will be very good production of fishes. To achieve this, appropriate amount of supplementary food as well as manure are to be supplied timely.
Indigenous and Exotic Carps for Composite Fish Culture
The economically important as well as cultivable herbivorous scaly fishes (having scales on body but not on head) without any teeth which are bony with air bladder as well as under the order cypriniformes are known as carps. Carps are of two types, such as indigenous and exotic carps.
Carps that are normally available in the inland waters of the Indian region are known as indigenous fish. Indigenous carps are of two kinds, such as major and minor carps. The carps that are big-sized cultivable fishes with rapid growth and high demand in the market are known as major carps. The carps that are comparatively small-sized with slow growth are known as minor carps, such as Bata (Labeo bata), Punti (Barbus ticto) etc.
Carps which have been imported from other countries and acclimatize to native place climate are known as exotic fish.
Advantages of composite fish culture
Selected species of indigenous and exotic carps are all compatible; they have different feeding habits and habitats in the same pond; so they are not competitors to each other for food and space. The foods of the different layers in pond-water are fully utilized by the carps in the composite fish culture or mixed culture. Induced breeding can also be done in the exotic carps and they are fast growing and the total production of fishes is very high and cost of production is less; this is also a profitable one.
Methodology of composite fish culture
The methodology of composite fish culture consists of the following major steps.
The Pre-stocking operations refers to preparation of the pond to ensure maximum survival and proper growth of cultured fishes and involve repairs of embankments, elimination of weeds and unwanted aquatic biota, and correction of physicochemical properties of water and soil.
Control of harmful aquatic vegetation
In view of the unfavorable effects excessive aquatic plants put forth on the pond with regard to living space, sunlight infiltration, oxygen circulation, sheltering of fish enemies, they should either be kept under check or cleared from the pond of composite fish culture.
Abolition of fish enemies
Draining of ponds or repeated netting in case of draining is not possible would help to remove the predators and complete removal is ensured by the application of piscicides. Derris powder was used as a piscicide. Because of procurement difficulties, chemical piscicides belonging to chlorinated hydrocarbons like Aldrin, Dieldrin, Endrin, Tafdrin-20 and organophosphate groups like Thiometon, D.D.V.P. were used as substitutes. But, in view of the harmful left over effects these leave in the pond, get stored in fish tissues and take a longer time to detoxify, their use is not suggested. Among the piscicides of native plant origin tried as substitutes are barks, roots, fruits and seeds variously of indigenous variety of derris, Derris trifoliata, Croton tigilium, Milletia pachycarpa, Barringtonia acutangula, Randia dumetorum, Walsura piscidia. At present for composite fish culture oil cake of Mahua (Bassia latifelia) containing 4–6 per cent saponio, being used, serves initially as a piscicide at 200–250 ppm and later acts as organic manure. Commercial bleaching powder, calcium hypochlorite, Ca(OCl)Cl, to be a good substitute for Mahua oilcake and also economical. Commercial bleaching powder is effective at 25–30 ppm (250–300 kg/ha-m.) affecting fishes within 15–30 minutes of application and killing all fishes including catfishes within 1–2 hrs. Crabs are also affected. Besides detoxification being quicker, bleaching powder disinfects the pond and helps in faster mineralization of organic matter.