Tamirabharani's Seven Endemic Fish Species Face Pollution and Habitat Loss

The Tamirabharani, the only river in Tamil Nadu that rises and drains into the sea entirely within the State, is home to a remarkably varied fish population. Surveys of its upstream, midstream and lower estuarine reaches have recorded 125 fish species, seven of which are found nowhere else.

These seven endemic species carry names drawn from the river and the places it passes through. Among them is Dawkinsia tambraparniei, known in Tamil as Tamirabharani Seval Kendai, which occurs both inside forest areas and in stretches downstream up to Srivaikundam. Its falling numbers have earned it a place on the IUCN Red List as an endangered species.

Another is Haludaria kannikattiensis, or the Kannikatti Melon Barb, named after a locality in the Kalakkad-Mundanthurai Tiger Reserve. It is a steno-endemic species, restricted to a single tributary inside the forest and found nowhere else. Neolissochilus tamiraparaniensis, a relatively small cold-water mahseer, was described by researchers J.A. Johnson and M. Arunachalam of Manonmaniam Sundaranar University.

The Tamirabharani Zodiac Loach, Mesonoemacheilus tambaraparniensis, locally called Ayrimeen, can survive only in clean, oxygen-rich water. Garra kalakadensis, or Kal Kendai, lives close to rocks in the forest stretch and takes its name from Kalakkad. Garra joshuai is another endemic species, while Hypselobarbus tamiraparaniei, a carp, was last recorded at Kallidaikurichi during a fish census held last year.

M. Mathivanan, senior research consultant at the Agasthyamalai Community Conservation Centre (ACCC), a unit of the Ashoka Trust for Research in Ecology and the Environment (ATREE) in Tirunelveli, said endemic species serve as indicators of a river system's health. Five of the seven continue to thrive, he said, while the two found outside forest areas face threats. The disappearance of these fish, he added, would signal the biological death of the river.

M. Vinod Kumar, a research consultant at ATREE-ACCC, said the decline is driven by pollution, habitat destruction, the loss of riparian vegetation, invasive fish and aquatic plants, bathing with soaps and shampoos, rituals on the banks, the dumping of pooja materials and clothes, and the discharge of untreated sewage.

Three invasive fish — tilapia, African catfish and a tank-cleaner species originally kept in aquariums and later released into the river — compete with native fish for food and prey on their eggs, Mr. Mathivanan said. Clearing riverside vegetation in the name of cleaning the river, he noted, also robs local species of space to survive and breed.