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Foreign threat to Kerala delicacy

New Delhi, Aug. 23: A hungry catfish from South America has sneaked into Kerala’s fresh waters and is threatening the native karimeen, a must-have for foreign tourists and a hit with chefs on Indian culinary shows.

The armoured catfish, Pterygoplichthus multiradiatus, is among at least four ornamental aquarium fishes that have slipped into Kerala’s fresh water canals where they are competing with local fish, according to researchers who have been monitoring fish species in the state.

The catfish is found in fresh water ponds in Thrissur district and in a canal in Thiruvananthapuram where it appears to have established a substantial population and is replacing local herbivorous fish, the researchers said in a report published in the journal Current Science, from the Indian Academy of Sciences.

“It’s a voracious feeder and a prolific breeder,” said Appukuttan Nair Bijukumar, an associate professor of aquatic biology and fisheries at the University of Kerala, Kariavattom. “The exotic catfish and pearl spot (karimeen) are both algae-eaters,” he said.

But the catfish is also a potential predator. “It can feed on the eggs of pearl spot and other local fish,” said Kaimal Krishnakumar, a team member and programme official at the Ashoka Trust for Research on Ecology and the Environment, Bangalore.

Scientists have also observed fairly large populations of two other freshwater fish species, the platy fish and the guppy, natives of central and South America, in the Chalakudy river near Thrissur district in recent years.

In another survey last year, biologists collected 15 males and six females of another aquarium fish — the three-spot gourami, a native of Sumatra — from Vembanad lake in Alappuzha district, although its ecological impact is unclear.

The researchers believe the ornamental fish moved into the fresh water either through accidental or intentional release of aquarium fish. Aquarium fish keeping is popular in the state.

Kerala is India’s third largest ornamental fish-breeding state and the Marine Products Export Development Authority in Kochi estimates that the state has nearly 500 fish breeding units.

“When fish outgrow their aquariums, people may just throw them into freshwater ponds,” Krishnakumar said. “We also have open pond breeding. The fish may escape into the local waters when such ponds overflow during rains.”

Ecologists caution that exotic species when introduced into new habitats have the potential to proliferate wildly.

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