Crayfish plague

Aphanomyces astaci


Photo credit: ©Bram Koese
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.
  • 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.
It is present in Ireland and Northern Ireland. To date, there have been seven outbreaks of crayfish plague on Irish rivers in 2016/2017 but as yet no records of American signal crayfish being present. As of the 17th September 2018 there is confirmation of a further outbreak at the headwater of the River Balckwater near Aughentaine. It would suggest that its pathway 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
More information can be seen on NBDC and NBN Atlas NI.
You can help by reporting any sightings:

Static Distribution Map as of December 2019 - Courtesy of CEDaR

Image details: Signal crayfish (Pacifastacus leniusculus) with melanised spots (an immune system reaction) on carapax (a) and soft abdominal cuticle (b) caused by Aphanomyces astaci infection. Photo ©: David Strand, National Veterinary Institute, Norway.    

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland