A prehistoric "vampire" fish has been found by staff at a power station in Kent during a routine inspection.
Sea lamprey use sucker-like teeth to drink the blood of their prey
The three-foot-long sea lamprey, which attacks other fish with suckers, was taken in with the water supply for the Kingsnorth Power Station in Rochester.
The Environment Agency said it was one of the first to be found in the Medway Estuary or south-east England.
The tubular, eel-like fish uses one set of sucker-like teeth to hold its prey and a second to suck their blood.
The live specimen was spotted by power station staff carrying out a routine inspection on Wednesday.
Bill Jones, the plant's nature warden, said he had called the Environment Agency immediately.
"I knew as soon as I saw it that it had to be pretty unusual," he said.
"At over three feet long it gave me quite a shock when I pulled this one out of the water.
"Sea lampreys look quite like eels and have sucker-like mouths with two sets of teeth that they use to cling on to other fish while they drink their blood."
Food of kings
Lampreys have fossil records going back some 340 million years to the Carboniferous period and have barely changed since then.
The Environment Agency said the fish only lived in very clean water and it was "pretty exceptional" to find one in the Medway.
They were an important source of food from Roman times onwards, and both King Henry I and King John of England reputedly died from gorging themselves on too much lamprey.
However, their numbers and geographical spread have been restricted by pollution and human interference with the rivers where they live and breed.
Mr Jones said he had recorded more than 60 species of fish in the River Medway at Kingsnorth.
The site also has rare birds and wildlife, attracting more than 2,000 visitors each year.