THOOTHUKUDI: Volunteers of the 13th Thamirabarani waterbird census have found the presence of invasive South American Suckermouth armoured catfishes in many water tanks. Attributing the loss of much native fish breeds to the invasive breed, environmentalists sought effective measures to control the African catfish population as well. J Thomas Mathibalan, president of Pearl city Nature Trust told TNIE he noticed the suckermouth catfish at Perur, Perungulam and Srivaikuntam Kaspa tanks.
"It has been in the local tanks for the past few years and eating into the population of the indigenous species. After the introduction of the alien fishes, the native species like Uluvai, Chellapodi, Vilanku, Kulathuvazhai, Mankiluru, Pannichethai, Aral and many others are not found in the irrigation tanks of Thamirabarani river basin," he said.
The suckermouth catfishes are also present in the tanks fed by Thamirabarani river in Tirunelveli", said Francis, who was part of the survey and is a zoology student at St Xavier's college in Palayamkottai.
A resident of Servaikaranmadam, Saravanan, said he used to catch native fishes, including Chellakottan, Vannathi, Nattu Theli, Kuravai, Pothikutti Kokkumeen, Thamirabaranei, Panai eri and Karupu Soppu kendai from the Iruvappapuram-Peikulam, Manjalneerkayal kulam, Arumugamangalamkulam tanks and Thamirabarani river at Eral 15 years ago.
These species have now vanished from the Thamirabarani river basin, he stated.
Thamirabarani river, fed by several tributaries flowing down the eastern slopes of western ghats, is home to over 75 fish species including seven species named after a locality or the river Thamirabarani - Garra Kalakadensis, Garra joshuai, Haludaria Kannikatensis, Hypselobarbus tamiraparaniei, Mesonoemaceilus tambraparniensis, Neolissochilus tamiraparaniensis and Dawkinsia tambraparaniei.
The suckermouth catfish found in the irrigation tanks is native to the South American floodplain lakes and marshes. Scientists say the species is traded globally as an aquarium pet used as 'cleaner' to remove the algae and other fish wastes.
"It might have reached the water bodies after being released by the aquarium owners and hobbyists. Being omnivorous fish, they can devour native fish juveniles in the wetlands. Despite appealing to ban this species from culture and import, no action has been taken by the state and union governments," they added.
Speaking to TNIE, Dr Johnson, senior scientist at Wildlife Institute of India (WII), Dehradun, said that the Amazon Armoured Sailfin catfish is one of the worst aquatic bio-invasive species in the world. "It enters mainly through the ornamental aquarium trade. Aquarists keep this animal as a pet and release it into nearby aquatic habitats without knowing its impacts.
Mushrooming of unorganized ornamental fish farming along the riverside is another way for the fish to enter the river system," said Johnson, who worked in the wetlands of the Thamirabarani river basin between 1995 to 2003. He contended that still there is no dedicated survey about the impact of invasive fishes on the indigenous species of the perennial rivers of Tamil Nadu.
"Many agencies have a role in introducing such alien species to the water bodies with regards to production and exports, an inter-departmental coordination committee may be formed to control the menace of invasive species. The presence of alien fishes would affect the native fish stock in the water body, which in turn affect fish-eating and migratory birds coming to Thamirabarani river. This causes serious consequences to the entire ecology," he said.
Dr Sandiliyan, a former fellow on Invasive Alien Species, said the suckermouth catfish had seeped into all the rivers in the country. "Though it is invasive, there is neither a data set nor a systematic study available with the government agencies to prove its adverse impact. The National Biodiversity Board (NBA) should generate a pan-India level data/mapping of Invasive Alien Species through the Biodiversity management committee (BMC) functioning in every village under the State Biodiversity Boards (SBBs)," he opined.