Poly Culture/Mixed Culture/Composite Fish Culture:
In order to achieve highest production per unit area of water bodies, fast growing compatible species of different feeding habits, different growth rate and different weight class are stocked or cultured together in the same water bodies so that all ecological niches are used or exploited by that species. This technique of culture of different aquatic organisms is known as composite culture or poly culture, or mixed farming. This technique is based on principle that all compatible species should be stocked to make no harm to each species. There is no competition between the cultured species and they may have the beneficial effect on the growth of others.
To achieve the maximum yield from any water bodies the very common combination of culture is done by three species of IMC. i.e. Catla catla, Labeo rohita, and Cirrhinus mrigala in 3:4:4 ratios. This method is very common in
The culture of three species of IMC with correct ratios is an example of appropriate selection of species with maximum utilization of pond with different zones. However the mixed farming is done by other ways by using exotic carps – Common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and Silver carp (Hypophthalmichthys molitrix).
Feeding habit of different species:
Catla catla – a surface feeder consuming zooplankton and detritus.
Silver Carp – a surface feeder consuming phytoplankton and other vegetative parts from surface
Labeo rohita – column feeder consuming decaying plants
Grass Carp - column feeder feeds on both coarse and macro vegetation.
Cirrhinus mrigala – bottom feeder consume decaying plants and detritus.
Common Carp – an omnivore and scavenger of both animals and plants.
From above feeding habit we can see that the ecological niches are well distributed among all species and there is no competition. Silver carp though a surface feeder, they consume phytoplankton where as other surface feeder Catla used zooplankton as their food. The common carp is omnivorous utilizing mainly the food which does not take Cirrhinus mrigala. The grass carp is known as efficient eater of macro-vegetation and all noxious and excessive vegetation growth can be controlled by using this species. Rather their faecal matters further serve as the food of common carps and also accelerate the plankton production of pond water.
The ratios used in six species culture are –
Common carp (Cyprinus carpio)
Grass carp (Ctenopharyngodon idella) 5 5 25
Silver carp (Hypophthalmichthys molitrix) 2 3 1
However the species combination entirely depends on the choice of culturists, area of pond, market value of individual species and climatic and ecological conditions of pond water.
In certain cases freshwater prawns (Macrobrachium rosenbergii) are also released. They are mostly carnivore and mostly feeds with supplied food and do not compete with carps. The faecal matter of fish also serves as additional sources of food to prawns, which are also detritus feeder or scavenger.
Stocking density: Stocking density is generally kept 5000-6000 fingerlings per ha. Stocking rate and proportion of fingerlings depends upon the availability of natural foods, the rate of fertilization and physiochemical condition of water.
Annual Yield: It was found that the average yield of indigenous major carps in intensive mixed farming is about 4000kg/ha/yr. Yield of exotic carp is about 3000kg/ha/yr. In mixed poly culture of IMC and Exotic carp the yield is about 8000kg/ha/yr. If prawns are released, average output of prawn is about 450-500kg/kg/ha. Further rising of output can be done if two crops in a year can culture. In that case the annual out put will be 11,000Kg of fish/ha. and 800-1000kg of prawn/ha of water bodies.
The low cost coupled with high yield in composite fish culture of six species will help spread the practice over the entire country. Extension services and programmes envisaging field demonstration, dissemination of relevant information will go a long way in popularization and earlier adoption of the technique. It has been found that the hypophysation in case of exotic carps as well as in case of indigenous. Thus the problem of seed will not encounter in the way of composite culture.
Experiment has also been conducted on integration of aquaculture with livestock rearing which can reduce the cost of fish production. In composite culture introduction of various types of foods into the pond (most common: rice bran and oil cake) can maximize the production of fish as well as prawns.