The US Government is to tighten rules on importing a species of predatory fish amid fears it could devastate local ecosystems.

Interior Secretary Gale Norton will announce a series of measures after the northern snakehead fish, which is native to Asia, was found in lakes in seven states.

If they got into the larger [water] system, they could alter the food chain and displace other species

John Surrick Maryland Department of Natural Resources.

The fish, which can grow up to three feet (one metre) long and "walk" on land, are believed to have been dumped by a resident in Maryland who imported them to make soup in a Chinese restaurant.

The snakehead eats other fish and pondlife and can survive out of water for up to three days.

Risk of escape

Officials are considering ways to destroy the fish, including poisoning the lake in Maryland where at least 80 baby snakeheads have been found.

Scientists are considering poisoning the fish

Draining the lakes runs a risk of letting the fish escape to other nearby lakes and streams.

"If they got into the larger [water] system, they could alter the food chain and displace other species," said John Surrick, from the Maryland Department of Natural Resources.

The fish, which have heads shaped like a snake's, can eat other fish, frogs, birds and even small mammals.

"You're talking about a total rearrangement of the food chain when you introduce a top predator like this," said Walter Courtenay, from the US Geological Survey in Florida.

Culinary delight

The interior secretary will propose adding 28 species of snakehead fish to a list of imports which require a special permit.

Snakehead fish

Up to three feet (one metre) long Able to "walk" on land Devour pondlife and small mammals Can survive three days out of water

The measure would make it illegal to trade the fish across state lines.

Snakehead fish are brought into the US for culinary use, and can be eaten smoked or dried.

They are an Asian delicacy, and, with their ugly wide mouths and heavy scales, people in some parts of Thailand and Burma believe the snakeheads to be reincarnated sinners.