Crayfish plague

Crayfish plague (Aphanomyces astaci) is a highly infectious disease of all crayfish of non North American origin. The causal agent is an Oomycete (water mould or downy mildew). Crayfish plague is now widespread in Europe as well as in North America. 

According to The Fish Site;

• The European crayfish species, the Noble crayfish (Astacus astacus) of north-west Europe, the stone crayfish (Austropotamobius pallipes) of south-west and west Europe, the related (Austropotamobius torrentium) (mountain streams of south-west Europe) and the slender clawed or Turkish crayfish (Astacus leptodactylus) of eastern Europe and Asia Minor are all highly susceptible.
• The reservoir for the original infections in the 19th century was never established, but the post-1960s extensions are largely linked to movements of North American crayfish introduced more recently for purposes of crayfish farming.
• Transmission has also resulted from contaminated crayfish traps and other contaminated equipment along with the movement of fish stocks from one body of water to another or contaminated fishing gear or boots.
• Infected crayfish may present a wide range of gross signs of infection or none at all. Focal whitening of local areas of musculature beneath transparent areas of thin cuticle, especially of the ventral abdomen and in the periopod (limb) joints, often accompanied by even more localised brown melanisation, is the most consistent sign.

 

 

(From CABI Aphanomyces astaci | CABI Compendium (cabidigitallibrary.org))

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• In the terminal stages of infection, animals show a limited range of behavioural signs, principally a loss of the normal aversion to bright light (they are seen in open water in daylight) later accompanied by a loss of limb co-ordination, which produces an effect that has been described as walking on stilts
• Eventually, animals lose their balance and fall onto their backs before dying
• The disease can cause a range of visible external lesions on crayfish e.g. fungal growth on soft parts of the shell, brown/black spots on the carapace, however this is difficult to identify without the help of an expert

 

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It is present in Ireland and Northern Ireland:

Crayfish plague has been recorded in both Ireland and Northern Ireland.

1. Currently there is a new outbreak on the Upper Ballinderry River catchment – confirmed by the Marine Institute on the 14th September 2023 – news post 
2. In 2018 in Northern Ireland it was recorded in the headwaters of the River Blackwater near Aughentaine, Co. Tyrone, see news post for more details.

The following rivers in Ireland have also been affected by crayfish plague;

• River Bruskey/Erne (Co. Cavan; detected 2015)
• River Suir (Co. Tipperary/Waterford, detected 2017)
• River Deel (Co. Limerick, 2017)
• River Barrow (Co. Carlow 2017)
• River Lorrha (Co. Tipperary, 2017)
• River Al (Co. Westmeath, 2018)
• River Maigue (Co. Limerick, 2019)
• River Clare (Co. Galway/Mayo, 2019)
• River Nore (Co. Kilkenny, 2019) 
• River Clodiagh (Co. Laois/Offaly, 2021)

Further details can be found on invasives.ie.

Despite a number of outbreaks of crayfish plague, as yet no records of invasive non-native crayfish have been recorded.

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How did it get here?

Pathways of introduction must have been either;

1. accidentally on contaminated equipment (e.g. wet fishing gear, canoes/kayaks, boats etc used recently in affected waters in the UK or elsewhere)
2. or else non-native species have been illegally introduced to the area and have now passed the disease to the native White-clawed crayfish

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Methods of prevention:

• Do not import any invasive non-native species
• Report all sightings
• When using any water follow Check Clean Dry guidance.

	Check your equipment, boat, and clothing after leaving the water for mud, aquatic animals or plant material. Remove anything you find and leave it at the site.
	Clean everything thoroughly as soon as you can, paying attention to areas that are damp or hard to access. Use hot water if possible.
	Dry everything for as long as you can before using elsewhere as some invasive plants and animals can survive for over two weeks in damp conditions.

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You can help by reporting any sightings:

• Centre for Environmental Data & Recording (CEDaR) – Or via the iRecord App.

For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email: invasivespecies@daera-ni.gov.uk