Conservationists have urged the public not to release unwanted pets into the wild after two piranha-like fish were discovered in a freshwater pond in Somerset.

The red-bellied pacu, which have sharp top and bottom teeth and are native to the Amazon and Orinoco river basins in Brazil, were both more than 50 centimetres long and weighed over eight pounds.

Experts believe the fish were deliberately dumped in the pond.

“Given that Bermuda is home to at least two endemic species of killifishes which only live in our ponds, we are extremely concerned that pacu could become established in the wrong wetlands,” said wildlife ecologist Mark Outerbridge.

Dr Outerbridge told The Royal Gazette it was unclear whether the fish had reproduced locally, but staff from the Department of Conservation Services and the Department of Environmental Protection were closely monitoring the pond. He added: “We urge the public not to release unwanted pets into the environment because of their potential to disrupt native ecosystems and introduce pathogens.

“We also want to encourage pet owners to have an ethical contingency plan for when they tire of looking after a long-lived pet or when the pet outgrows their captive environment, which is of particular relevance when the animal or fish grows large.

“This plan should include identifying someone who is prepared to adopt and provide the necessary care for the animal or identify an organisation that will humanely euthanise the animal.”

Conservationists made the unusual discovery of the two pacu species after receiving reports from members of the public that large “carp-like” fish had been spotted in the pond.

Dr Outerbridge then went down to the freshwater pond to investigate further and caught two large pacu.

He believes there could be more in the pond.

He said: “One was a male which measured 55cm total body length and weighed 8.25lb, the other was a female which measured 53cm total body length and weighed 8.5lb.

“Pacu is a common name used in the aquarium trade to refer to several species of omnivorous South American freshwater fish that are related to the piranha.

“This species is native to the Amazon and Orinoco river basins in Brazil but is also a popular aquarium fish in the pet trade industry. Pet stores sell pacu when small — normally between five and eight centimetres — but may neglect to warn customers that fish growth is not inhibited by tank size, contrary to popular fish lore.”

Red-bellied pacu have been introduced in numerous states throughout the United States as well as in Europe, India and Papua New Guinea.

Dr Outerbridge said: “Red-bellied pacu can grow to 88cm total body length and weigh up to 55lb which makes caring for them in a captive tank environment expensive and extremely challenging.

“This often leads to hobbyists releasing fish into local waters. This species of fish is an opportunistic feeder. Its preferred diet in the wild is fruits, nuts and seeds; however it is also known to consume insects, zooplankton and small fish.”