Alien fish threat to wildlife

2008-12-07 00:00

Scientists have sounded an alert about an alien invader fish that has been found in KwaZulu-Natal.

The fish potentially pose such a serious threat that they will be controlled by environmental legislation currently being drafted.

Armoured catfish or “plecos” (Pterygoplichthys disjunctivus) have been found in the uMhlathuze and Nseleni rivers in the Empangeni district.

Native to south and central America, they are very popular with fish enthusiasts because they are attractive and help to keep fish tanks clean of algae. However, in natural water systems, they could pose a threat to indigenous fish stocks and subsistence and commercial fishing.

“These fish are of particular concern in KZN because the freshwater environment along the coast is suitable for them and they could invade extensive areas,” said Professor Paul Skelton, a freshwater fish expert and managing director of the SA Institute for Aquatic Biodiversity (SAIAB) in Grahamstown.

“We don’t know for sure how they got into local waters, but most likely they were released by, or escaped from, aquarists in the area.

“They have been in the aquarium trade for several decades now — I am not sure exactly when they first were introduced.”

He said plecos are easily distinguished from all African catfishes by their armour — a series of bony plates along the body. They also have a small ventral mouth shaped like a disc, and a tall, rayed dorsal fin with a small fleshy fin behind it.

Spokesman for Ezemvelo KZNWildlife Jeff Gaisford appealed “in the strongest terms” for people who own plecos not to release them into local rivers or dams.

“If you get tired of them, or they grow too big for your tank, please do not release them. You could be setting the devil loose in our natural waterways. They are alien invaders just the same as plant invaders. It could be like starting a cancer. Take them back to the supplier, destroy them or contact nature conservation officials.”

Robert Karssing, an aquatic research technologist at Ezemvelo and a keen fisherman, appealed to other fishermen who catch plecos in local waters not to release them.

“Freeze them, bring them to us, and report the location where they were caught. We will send the fish to the SAIAB for analysis,” he said.

The SA National Biodiversity Institute is drafting legislation to control invasive organisms, the regulations for the National Environmental Management: Biodiversity Act.

Plecos have been placed on the list of organisms for control, Skelton said.

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