Cauvery basin fishes face extinction

Chennai: The indigenous fish population in Cauvery river basin is facing a threat of extinction due to the invasion of Amazon Sailfin Catfish, commonly known as tank cleaner fish, which outranked other edible fishes in the region.

This non-edible and unmarketable fish which was originally introduced as a pet has now turned into a menace as it outranked all other edible fishes both in abundance and biomass production in the local fresh water eco-system.

“In our study, the percentage of Amazon Sailfin Catfish occurred during the sampling in various parts of Cauvery and Vaigai river basin ranges from 10 per cent to 90 per cent,” said S. Chandrasekaran, invasion ecologist and associate professor, Department of Plant Science, Madurai Kamaraj University.

The team headed by S.Chandrasekaran undertook a study in Thanjavur, Tiruchy, Madurai and Ramanathapuram districts to know the extent of invasion of this South American fish and its impact on the local edible fish population.

The study was sponsored by State Planning Commission’s Tamil Nadu State Land Use Research Board. A total of 24 field sites had been chosen in these districts and multiple samplings were conducted regularly.

“From our field observations, we noted that Amazon Sailfin Catfish had completely invaded the river ecosystem and the water bodies that depend on the Cauvery and Vaigai river basin of Tamil Nadu. The invasion episode is worse in the Cauvery river system,” he said.

The impact was less in the Vaigai river basin as the water flow is much less compared to Cauvery. “In the freshwater ecosystem of Cauvery river basin, more than one-third of the occurred fishes in our sampling are ‘suckermouth catfishes’,” he added.  

The presence of the fish was found both in large surface water bodies like a dam, lake and small surfaced irrigation channels like canals.  “The fish inhabit in all the polluted sites, which serves as a haven to these populations of fishes, while the native population of fishes and animals cease to survive in such polluted waters,” he observed.

Further explaining the peculiar ability of these fishes, he said, “The peculiar ability of these invasive populations of fishes is their ability to identify empty niches such as wells and drainages that don’t dry out throughout the year.”
When the water flows, it gives them a strategic advantage of reproduction capable population over the native population of fishes. The study has found that this fish uses the habitat of local edible fishes and competing for the available food resource of edible fishes. The hard bony plates of the suckermouth catfish also damage the body of the edible fishes during the mass movement.

The invasion of this fish also affects local fishermen community as the reduction of native fish populations severely affecting their economic conditions. It also reduces the quality and marketability of the local edible fishes.

The research team further intends to study the economic impact of the invasion and measures to control the population of this fish.   “A lot of effort, time and money spent to eliminate the invasive species in their local water bodies only to see their population bounce back in a matter of months. We intend to develop something like pesticide to control their population,” he concluded.