Publication Abstract

Aphanomycosis of crayfish: crayfish plague. A report prepared for the Environment Agency and English nature.

DJ Alderman

Crayfish plague is an extremely virulent fungal disease of European crayfish species, the white clawed or stone crayfish of Western Europe Austropotamobius pallipes, the Noble crayfish of northern Europe Astacus astacus and the narrow clawed crayfish of Eastern Europe, Astacus leptodactylus. The white claw crayfish A. pallipes is the indigenous native crayfish of the British Isles. Until the early 1980s there were extensive healthy populations of this crayfish in almost all suitable alkaline river and lake environments in England and Wales as far north as Northumberland. The conservation importance of this native crayfish is widely recognised. After some delay in 1986 it was protected in Britain under Schedule 5 of the Wildlife and Countryside Act 1981. It is also listed in Annexes II and V of the EU Habitat and Species Directive (1992) with a requirement that Special Areas of Conservation should be set up to protect it. It is additionally classified as globally threatened by IUCN/WCMC, is listed in Appendix III of the Bern Convention (the Red List) and now appears as a species of conservation priority on the UK Government's Biodiversity Action Plan.

Crayfish plague caused by the Oomycete fungus A. astaci first appeared in Europe in the third quarter of the 19^th century and spread remorselessly throughout Europe. Within 100 years only Norway, the British Isles, Greece and Turkey were free of the disease. Infection reached the British Isles in about 1980 in signal crayfish, Pacifastacus leniusculus that had been imported as part of attempts to create a commercial crayfish farming industry. The signal crayfish is a N. American species which is resistant to crayfish plague (which is itself of N. American origin) and frequently acts as an asymptomatic carrier. So severe is the impact of crayfish plague in susceptible European crayfish that infection eliminates entire populations and in over 100 years no evidence of resistance has appeared. Since the arrival of crayfish plague in the British Isles some twenty years ago populations of native crayfish have been severely affected.

This report provides a general review of the literature of crayfish plague, including an overview of its spread through the British Isles from CEFAS records. Information on current diagnostic methods from the Office International des Epizooties (OIE) Aquatic Disease Manual is provided. Information on the taxonomy, morphology and physiology of the pathogen is reviewed, together with the pathogenicity and pathology of the disease and current means of prevention and control.

In the second part of this report the risks of the disease spreading further are considered, particularly in relation to stocking movements of fish. The Prohibition of Keeping of Live Fish (Crayfish) Order, 1996, now controls keeping of exotic crayfish so that the primary risk of transfer of infection to new areas is believed to lie with movements of contaminated equipment and transport of fish temporarily contaminated by A. astaci. That this is a practical risk has been demonstrated both experimentally and anecdotally in the field.

The Environment Agency has statutory powers under Section 30 SFFA in regard to introductions of fish into inland waters and responsibilities for conservation under the Environment Act. English Nature has statutory powers to prevent introductions of fish from sites containing signal crayfish into waters designated for the white clawed crayfish. The Environment Agency and English Nature have commissioned this report to provide them with an up to date review of the literature of crayfish plague and in particular to assist them exercising their statutory responsibilities by providing a good scientific background to support their decision making.

Recommendations are made on actions that may be taken to mitigate the risks of such transfers, on research needs to improve ability to diagnose infection particularly of carrier state. Molecular methods have major advantages, but need full validation before they can be implemented as diagnostic tools. The need for a suitable fungicide to use to aid in mitigation of transfer risks is emphasised and the limitations on the type of product that can be used is discussed in relation to veterinary medicines legislation is considered. Research needs to support this use are outlined.

Reference:

D.J Alderman 2003. Aphanomycosis of crayfish: crayfish plague. A report prepared for the Environment Agency and English nature. R&D Technical report w2-064.