Conservationists fear a foreign crayfish could devastate Britain's rivers if it is allowed to escape into the wild.
American crayfish, Chinese crabs and French fish already rub shoulders with native species in our rivers.
Now a hybrid species called a marble crayfish is becoming popular within the aquarium trade. And unlike most other species the marble - or promcambarus - does not need a mate to breed.
Adults can produce up to 270 eggs every eight weeks all year round, with maturity being reached 25-35 weeks after hatching, so only one individual animal would need to be released to establish a population.
Cefas - the Lowestoft-based Centre for Environment, Fisheries and Aquaculture Science - said it had become aware of an increase in the numbers of alien crayfish for sale in aquatic outlets and garden centres.
It believes marbled crayfish first appeared in the aquarium trade in Germany and Austria in the mid-1990s.
“Wild populations of this species have already been confirmed in Germany and possibly Holland,” a spokesman said.
“Therefore this species would become established in British waters if released.
“It is imperative that this species is stopped from spreading into the wild.”
The Fisheries and Angling Conservation Trust (FACT) also fears it could carry the so-called crayfish plague, a disease which kills off our native white-clawed crayfish. It is meeting next month to discuss the problem.
Its director Mike Heylin said: “We still don't know what the impacts of signal crayfish are or how to manage it because the research just isn't being done.
“Another species like this would take a lot of fish eggs at spawning time and also dig up weed in lakes.”
Cefas said anyone who had bought marbled crayfish, or who may have information concerning the source of this species in the UK, should call the Fish Health Inspectorate at Cefas on 01305 206673 or e-mail Fish.Health.Inspectorate@Cefas.co.uk .
Click here for more and a picture of one.