June 30, 2003


Scientists dispel fears of piranha invasion in Cat Tien Reserve
Silver pacus like these caused the piranha panic. — VNA/VNS Photo Xuan Truong

HCM CITY — Alarms raised last week about voracious piranhas swimming in ponds in the southern Cat Tien Natural Reserve have been called unfounded by a group of biologists who investigated the reports.

The carnivorous fish in question turned out to be newly-imported silver pacu (colossoma brachypomum), according to the team which just returned to HCM City from the Cat Tien jungle. Some farmers are raising the fish in their ponds downstream of the Dong Nai River.

The probe followed strong rumours which even caused managers of the Cat Tien reserve buffer zone to print leaflets warning locals of the danger of raising piranhas. Once the fish infiltrate the natural water environment, they could cause a serious environmental hazard overnight, the leaflets warned.

The researchers, from the Aquatic Product Research Institute II and the Dong Nai Provincial Department of Aquatic Product Resources Protection, made their report on Thursday after visiting several fish farms by the Dong Nai.

They revealed in their report that the new fish is also a kind of voracious fresh-water breed, greedy and able to devour any plant or insect in its path.

The Fisheries Ministry allowed in 1998 to import and raise this variety on an experimental basis, the biologists reported. And, according to deputy director of the Aquatic Product Research Institute I, Dr Pham Anh Tuan, it is completely different from the piranha.

The latter has a large mouth and sharp teeth on both jaws, and feeds on flesh, both dead and alive. The colossoma brachypomum has seesaw-wedged teeth which are large but not sharp.

Tuan said his institute has experimented with raising the fish, both in isolation and in a mixed environment including other varieties of fish, and researched its biological characters, including breeding.

It adapts well to any tropical environment but when left unfed, will attack other living fish, making it risky to let it enter the natural environment, he warned.

Old bogey

A possible reason the piranha alarm found currency is the fact that 15 of the deadly fish were imported from Taiwan in 1998 for aquariums. When a researcher stumbled over one of them when making a survey of colossoma bra-chypomum, he promptly blew the whistle, bringing a Fisheries Ministry ban.

Dr Hoang Duc Dat, a biologist at the Institute of Tropical Biology and a member of the team compiling Viet Nam’s flora and fauna dictionary, expressed relief that the fish turned out to be pacus rather than piranhas. Though he admitted the silver pacu was sometimes carnivorous, it was a different kettle of fish from the piranha which "hunts aggressively for living prey."

It is not as if any carnivorous fish would automatically be banned from being raised, he pointed out. In illustration, he pointed to the loc, or striped snake fish, commonly found in Viet Nam’s waters. Not only do they eat fish but also frogs and toads.

Man in hot seat wary

However, the man responsible for tracking down the pacu upstream of the Dong Nai River, Nguyen Thanh Tung of the Aquatic Product Research Institute II, has a different opinion.

The head of the institute’s Environment and Aquatic Product Resources Department said even though the "peaceful" silver pacu is indeed not the piranha, its presence in the wild should be taken cognisance of.

He warned that since the pacu belongs to the same family as the piranha – meaning it can grow rapidly, eat any plant and occasionally fish, and live in large shoals – it could lead to a dangerous situation if allowed to freely develop in the wild.

Tung said the fisheries ministry should put a cap on raising the fish on an experimental basis and not encourage farmers to expand their breeding.

Besides, he said, the pacu should strictly be contained in ponds and not allowed to enter the wild where it might devour indigenous breeds, eventually destabilising the entire ecosystem.

"In the long run, it is up to the fisheries ministry to consider whether raising silver pacu is sustainable in Viet Nam," Tung said. — VNS

Copyright Vietnam News