An aggressive invader eclipses native fish

A file photo of a youth with Tilapia fish from a lake in South Chennai.— Photo: Shaju John  

It is an aggressive invasive entrant to India, now occupying every single water body in the State, elbowing out many native species. Tilapia, known as Jilepi in Tamil is a fish native to Africa and parts of West Asia.

A perennial breeder capable of tolerating pollution, it is blamed by scientists for depleting resources that earlier were shared by several other species.

“Many native freshwater fishes including Rasbora, Danio, Macropodus and Barbus and other local cat fish species have borne the brunt of the tilapia invasion. Tilapia survives in water with very low oxygen level and its eggs retain life even in dry conditions. It has destroyed the habitat of native species which are already decimated by pollution,” said a scientist at the Fisheries Training and Research Centre in Parakkai, Kanyakumari district.

So real was the threat that the Fisheries Research Committee of India imposed a ban in 1959 on Oreochromis mossambicus , a tilapia species introduced in 1952.

The Nile tilapia introduced in 1970 then emerged as an important component for aquaculture in India and became famous as ‘aquatic chicken’, the National Fisheries Development Board in 2015 issued guidelines for responsible farming of the fish.

“Tilapia is omnivorous and exemplifies parental care while many native species are careless parents. Tilapia dig burrows to build nests and both male and female guard their young till they reach the juvenile stage. When predators approach, they keep the juveniles in their mouth,” said M. Arunachalam, former head, Department of fisheries, Manonmaniam Sundaranar University.

The National Fisheries Development Board says a high population of the species has affected the fisheries in several reservoirs and lakes as in Vaigai, Krishnagiri, Amaravati, Bhavanisagar, Tirumoorthy, Uppar and Pambar reservoirs in Tamil Nadu, Walayar, Malampuzha, Pothundy, Meenkara, Chulliar and Peechi reservoirs of Kerala, Kabini reservoir of Karnataka and Jaisamand lake in Rajasthan.

“Introduction of Oreochromis mossambicus in Jaisamand lake not only resulted in reduction of average weight of major carp, but also posed a threat to mahseers ( Tor tor and T. putitora ), which are on the verge of extinction,” the Board reported.

“In 2005, the Yamuna harboured only a negligible quantity of Nile tilapia, but in two years, its proportion rose to about 3.5 per cent of total fish species in the river. In the Ganges river system, the proportion of tilapia is about seven per cent of total fish species, the report said.

Dr. Arunachalam said even though O. mossambicus was banned , it wreaked havoc and proved a threat to native biodiversity. “As a signatory of the Convention on Biological Diversity, India has a duty to protect its wild germ plasm before it is totally eradicated by exotic species,” he said.

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Printable version | May 2, 2021 7:14:00 PM |

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