Walkers around Ulsoor lake came across the unexpected not once but twice in recent weeks when a huge mass of dead fish floated past them. But if fish are dying in lakes due to contamination caused by sewage discharged into them and other man-made factors, there is another lurking threat to the native fish species in these waters and it comes from the ‘Catfish,’ a species from Africa imported into the country about two decades ago.
Introduced in Brazil, Vietnam, Indonesia and India in 1980 for aquaculture, the Clarias gariepinus, popularly known as the African Catfish, is now posing a major threat to Indian fish species.
Growing upto three feet in length and weighing nearly 60kg, this monster is known to prey on native fish. Unfortunately there is no predatory fish that can hunt it in turn in India. This extremely fast growing and highly carnivorous fish was surreptitiously introduced into the country through Bangladesh, but has now been banned by the Union government under section 5 of the Environment Protection Act, which prohibits its culture in ponds and tanks.
But with the state government doing little to enforce the ban in Karnataka, the cannibalistic fish has already entered the Cauvery river system and is now found in almost all lakes of the city, posing a serious threat to their biodiversity.
The Karnataka State of Environment Report prepared by Prof. Madhav Gadgil in association with many other scientists across the country, was among the first to highlight the threat posed by the African Catfish.
Various studies of the aquatic diversity of the wetlands of Bengaluru conducted by scientists of the Indian Institute of Science (IISc) led by Dr T V Ramachandra also talk of the major threat to the native fish from the growing population of the African Catfish in these waters.
At a recent workshop on ways to revive the Bellandur and Varthur lakes, Dr Ramachandra demanded to know from Minister for Bengaluru Development and Town Planning , K J George, why the state continued to allow the introduction of this exotic species into the city’s water bodies. “ It is a serious crime,” he told him, adding, “ We have lost our native fish because of this."
But the African Catfish is also a threat to people as it feeds on waste accumulated on the lake bed. Those eating the fish can come down with arthritis, blood clots, and even cancer, warn scientists , who believe that the only solution is to completely eradicate the species from all the state’s wetlands as has been attempted by the Andhra Pradesh Fisheries Department, which has taken drastic action to destroy all stocks of the fish since 2004.
