Illegal Marbled crayfish poses threat to UK

ea3caa31-cd2c-4347-bab1-8c995d2173f0

Editor's Picks
Features Post
The brightest pupils
04 October 2021
Features Post
Dealing with egg ‘fungus’
04 October 2021
Features Post
Rathbun’s tetra in the wild
13 September 2021
Fishkeeping News Post
Report: 2021 BKKS National Koi Show results
13 September 2021
Features Post
The World's forgotten fishes
16 August 2021


Fisheries Inspectors have warned that an illegal crayfish currently on sale in UK aquarium shops could pose a significant risk to the environment.

Marbled crayfish or Marmokrebs are the first recorded species that are known to be capable of asexual reproduction, so the escape or illegal release of a single specimen could see the species becoming established in UK waters.

Adult Marbled crayfish produce up to 270 eggs every couple of months and reach sexual maturity at an age of 25-35 weeks, so could quickly become established. (See Parthenogenetic marmokrebs has sex on its own, News, July 30, 2004)

The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) and the Department for Environment, Food and Rural Affairs (DEFRA) told Practical Fishkeeping that they had become aware of increasing numbers of non-native crayfish on sale in the UK, including the Marbled crayfish.

Rapid reproductionThey fear that the high rate of reproduction in the species could see fishkeepers passing on excess offspring to other fishkeepers or local shops, which increases the risk of the species getting into UK waters.

The species, which is believed to be a member of the Procambarus genus from North America, can survive cold winters and has already become established in Germany after specimens were released by fishkeepers.

Dr Paul Stebbing, a crayfish specialist at the 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."

Disease carrierThe species also acts as a carrier for a fungal infection known as 'crayfish plague', to which the UK's only native crayfish species is highly susceptible.

Crayfish plague is believed to have been introduced into the UK following the introduction of Signal crayfish from North America and has had a serious impact upon native crayfish stocks.

Since 1996 it has been illegal to keep non-native crayfish in aquaria, with the notable exception of a single species, Cherax quadricarinatus.

CEFAS says that no licences have, or will be issued for keeping temperate species, such as the Marbled crayfish, as pets so readers are advised not to purchase the animals.

CEFAS said: "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 [email protected]

"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."

Marbled crayfishThe Marbled crayfish first appeared in the aquarium trade in Germany in the 1990s.

By 2004, German authorities were reporting that it had become well-established in the wild in several places.

For more information on the species see: Vogt, G., Tolley, L. and Scholtz, G. (2004) - Life stages and reproductive components of the marmokrebs (marbled crayfish), the first parthenogenetic decapod crustacean. Journal of Morphology, 2004, Sep, 261 (3) 286-311.