The arrival in the UK of a foreign ornamental crayfish species via the aquarium trade could put native crayfish species under further severe pressure.

Scientists at Cefas (the Centre for Environment, Fisheries & Aquaculture Science) and Defra (the Department for Environment, Food and Rural Affairs) have recently become aware of increasing numbers of non-native crayfish for sale in UK aquatic outlets and garden centres. Of particular concern is the number of marbled crayfish being found.

The marbled crayfish (Procambarus sp.) is the first recorded crayfish capable of asexual reproduction (parthenogenesis). An adult is capable of producing up to 270 eggs every 8–9 weeks with sexual maturity being reached 25–35 weeks after hatching, under optimum conditions. This means that only one animal is required to establish a breeding population.

Because the marbled crayfish can reproduce so rapidly, hobbyists could pass excess stock onto other hobbyists, pet shops, or even release them into the wild. Marbled crayfish can survive in temperate water, so there is a concern that this alien species will become established in Great Britain if released. The release of any non-native species to the wild in Great Britain is an offence under the Wildlife and Countryside Act 1981.

Dr Paul Stebbing, a crayfish specialist at Cefas’ Fish Health Inspectorate, said: “To maintain their breeding programme, marbled crayfish use vast amounts of energy. So they are voracious feeders and will consume a broad range of aquatic plants and invertebrates, and scavenge on other food sources. This poses a risk that they may have a direct impact on native aquatic fauna and flora if released to natural waters.”

And there is more bad news: “Marbled crayfish act as carriers of the crayfish plague – a fungal infection to which our native crayfish species is highly susceptible,” said Dr Birgit Oidtmann, crayfish plague specialist at Cefas. “This same disease was brought into the UK by signal crayfish from North America, with serious impacts on native populations.”  more … /
It is illegal to keep non-native crayfish even as pets in England and Wales, except with a licence issued under the Prohibition of Keeping of Live Fish (Crayfish) Order 1996. No licences have been, or will be, issued to enable the keeping of temperate species such as the marbled crayfish as pets.

To help prevent the marbled crayfish spreading into the wild, Cefas advise that anyone holding marbled crayfish, or who may have information about UK sources of this species, should contact the Fish Health Inspectorate on 01305 206673 or email The Inspectorate will advise callers on the safe removal of any non-native crayfish in their possession, and provide advice to ensure that ornamental fish dealers do not continue to import such animals.


1.  Cefas is an internationally renowned scientific research and advisory establishment, based at Lowestoft since 1902. It also has laboratories at Burnham-on-Crouch and Weymouth, and a number of other facilities around the UK. The agency undertakes work on fisheries management, environment and biodiversity protection and aquaculture. For more detail about its range of activities visit

2.  The Fish Health Inspectorate (FHI), based at Cefas’ Weymouth laboratory, is dedicated to maintaining and improving fish and shellfish health in England and Wales. Its primary role is to act for Defra and the National Assembly for Wales, Agriculture Department (NAWAD) in undertaking statutory and inspection duties resulting from the EU Fish Health regime and other national legislation in the area of fish and shellfish health.

3.  The Inspectorate is responsible for health certification of fish and shellfish movements from other countries, and runs an enforcement programme aimed at preventing the illegal importation of these animals. It also has responsibility for the licensing of non-native crayfish and the enforcement of “keeping” legislation. For more about movement controls and enforcement visit,-imports-and-exports.aspx.

4.  Marbled crayfish, thought to be of North American origin, first appeared in the aquarium trade in Germany and Austria in the mid-1990s. The species has been released into natural waters in Europe, though its impact in these areas has yet to be assessed.

5.  A general licence allowing the tropical redclaw crayfish species (Cherax quadricarinatus) to be kept in the ornamental trade has been issued.