Fungal Diseases of Freshwater Crayfish

Fungal diseases are often reported to be the most important pathogens of freshwater crayfish. This is primarily due to one pathogen, Aphanomyces astaci, the causative agent for crayfish plague. Other fungi have been associated with the following diseases affecting freshwater crayfish:

Burn spot disease

Other fungal infections

Besides crayfish plague, most fungal diseases affecting freshwater crayfish are associated with poor water quality and therefore can be managed by environmental management. Fungicides or general disinfectants, such as formalin, may be used to treat valuable broodstock for fungal infections (eg. infestation of eggs). There are no cures for crayfish plague infection ­ typically 100% of susceptible crayfish species in a population will be killed after the fungus is introduced. Management strategies in affected areas therefore rely on stocking either resistant species, which are the American carrier species, or restocking with native species and education to lessen the likelihood of reintroduction of the fungus with carrier species or contaminated equipment. In Northern Europe the education program is impressive ­ the general public in this region have a very good understanding of the disease, it’s significance and what should be done to prevent its spread.

Crayfish plague

Crayfish plague was introduced into Europe with the introduction of American freshwater crayfish species in the mid 1800s and has been spreading ever since, resulting in the elimination of many native freshwater crayfish populations. An excellent review on the spread of crayfish plague is presented in Alderman (1996). David Alderman has included a shorter but updated account of the spread of crayfish plague in a consultancy report on the inactivation of A. astaci prepared for the Australian Quarantine and Inspection Service ­ click here to download the report from the AQIS website. Importantly, crayfish plague has continued to spread in Europe because American species continue to spread on the continent, by natural movements or due to stocking by humans (eg. the American signal crayfish and redswamp crayfish), and by movement of contaminated equipment such as crayfish traps.

Burn spot disease

Burn spot disease, often referred to as shell disease, is a common disease of freshwater crayfish which is caused by fungi and/or bacteria. The disease is characterised by progressive erosion of the exoskeleton and is fatal when large areas of the exoskeleton have been eroded. Fungal species involved with shell disease include Ramularia astaci, Cephalosporium leptodactyli and Didymaria cambari.

Other fungal infections

Fungi belonging to the genera Saprolegnia, Aphanomyces and Achlya are frequent opportunistic pathogens of freshwater crayfish. Typically infestation by these fungi is associated with poor water quality and other management issues. These fungi usually infest the regions of soft cuticle or wounds in the exoskeleton, the gills and eggs. Fusarium species have also been associated with disease in freshwater crayfish, and some reports suggest that some species or strains are highly pathogenic to freshwater crayfish.

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