Though the Fisheries Department of states like Karnataka has banned the culture of African catfish, considered by many as a menace to the whole freshwater ecosystem, interestingly Tamil Nadu, where the Kelavarapalli reservoir is situated, has not banned it.This fish fetch higher price than tilapia as there is a market for it in certain parts of this State. They enter the reservoir from culture ponds adjacent to river South Pennar during rain and floods. But Nile Tilapia, a dominant invasive fish found in the reservoir, has a positive impact on Indian major carps such as Catla catla, Labeo rohita and Cirrhinus mrigala.
Nile Tilapia, most abundant in the commercial catch and available throughout the year, still remains at limited levels.Phytoplankton and detritus form important food source of these groups. The littoral areas of Kelavarapalli reservoir are full of nests of Nile Tilapia and they breed during South-West Monsoon (July-September).There is heavy demand for this fish, especially from poor local people, as it is affordable to the lowest income group in the area.
The scientists modelled the reservoir ecosystem designing its food web and tracing the energy flow incorporating all living organisms and their interactions in the food web. This is the most advanced way of quantifying the flows in ecosystems so that scientific management of reservoir ecosystem can be done for sustainable fisheries management.The scientists used mass balance model to prove the validity of their findings. The study comes at a time when many in the fisheries sector have expressed their concern over the farming of invasive fish varieties, Nile Tilapia (Oreochromis niloticus), Mozambique Tilapia (O. mossambicus) and African catfish.
Since reservoirs are considered to be growing resource in India with enormous fish yield potential and supporting capture fisheries activities, the study is the first attempt to assess the impact of invasive fishes on reservoir ecosystem through ecosystem-based approach for management of reservoir fisheries. Its objective included documenting and quantifying the tropic structure of the reservoir, evaluation of the role of invasive species in the reservoir ecosystem and gaining an insight into the properties and development status of the ecosystem.
The study finds that this reservoir is relatively at a developmental stage or a young ecosystem which is vulnerable to disturbances (natural or anthropogenic).Though the production is high in young ecosystem, care should be taken not to exploit it indiscriminately. The study points to the need to take up some sort of conservation measure atleast during the breeding period of Nile Tilapia.