IS EXOTIC CATFISH Clarias gariepinus A THREAT TO FRESHWATER BIODIVERSITY?  A CASE STUDY FROM KERALA

catfish, Clarias griepinus, was illegally introduced in aquaculture by freshwater farmers, initially in West Bengal, then slowly spread to Andhra Pradesh, Uttar Pradesh, Bihar, Punjab, Kerala, Tamil Nadu and Kranataka. Though Government authorities banned this species in aquaculture in 1998 itself, breeding and culture of this species continued by the farmers in many place. Many people were transporting seed from West Bengal to Andhra Pradesh, Kerala, Uttar Pradesh and Punjab. Later the fish was reported from natural water bodies in several places. ICAR-NBFGR taken  up a study on impact of exotic fishes in India, in which we have done extensive sampling from different water bodies in Kerala. We observed established populations of African catfish in a temple pond in Kozhikode (Fig 1), Periyar Lake, Thekkady (Fig.2), Manathwady River in Wayanad, Anayirangal dam, Mattuppetti dam in Idukki.  From the survey in these areas, people told that earlier African catfish was not available in these areas and  after 2008 only these fishes started appearing in natural waters. In Panamaram River, African catfish started appearing in 2014 and after the flood in Kerala in August 2018, fish started appearing in nearby rivers also. Surveys were also conducted in Pampa and Manimala River, in Kerala which yielded an adult female specimen with matured ovaries (Fig 3). Fishes were sampled from Periyar lake for studying its biology and food and feeding. Fishermen reported the specimen as big as upto 15 kg but in our sampling we got specimen upto 7 kg. Though in our studies we got a number of specimens of African catfish from the lake but no matured specimen was observed. Fish gut was dominated by detritus (including digested matter) (47%), followed by plant materials (37%), insects/prawn/crab (10%), molluscs (4%) and fish (2%). Also observed that it may damage the habitats where they are present by raking the sand and mud in search of food. This is very detrimental for indigenous fish species. Fishermen from Periyar Lake told that after the appearance of the African catfish, the catch of other fishes reduced. Since predominantly its omnivorous nature, high fecundity and capacity to survive in adverse conditions, there is likely chance of establishing in more water bodies and there is an urgent need of removal of this invasive exotic catfish from our water bodies.