Crayfish, Freshwater Crayfish and Crayfish Plague

Crayfish plague is a fungal disease that has the potential to cause large-scale mortality of freshwater crayfish in Australia. At present, the disease does not occur  in Australia. However, it is important that state and territory governments and the red-claw, yabby and marron aquaculture industries are adequately prepared to manage a disease outbreak, because an incursion of the disease could devastate the  freshwater crayfish aquaculture industry as well as wild populations of crayfish. The aetiological agent of crayfish plague is the oomycete,  Aphanomyces astaci Schikora. Oomycetes (commonly called water moulds) are not considered to be ‘true fungi’ taxonomically, but have been placed in the phylum Oomycota. Within this phylum is the family Saprolegniaceae, which consists of the  Achlya,  Aphanomyces and  Saprolegnia genera, with some species being pathogens of crustaceans, fish and plants.

Crayfish

Giant Crayfish

Astaci is a branching, non-septate fungus that produces spores under conditions that are favourable for the particular substrain. The spores can survive in fresh water for a variable time depending on water temperature and chemistry. Motile zoospores measuring 8–15 μm emerge from spores and attach to new hosts in the
water body.

Freshwater Crayfish

Giant Freshwater Crayfish

Freshwater crayfish species from Australia, New Guinea, Japan and Europe are highly susceptible to crayfish plague; species from North America are more resistant but can die from the disease if their immune systems are stressed, such as by overcrowding or extreme weather. The disease has not been reported in aquatic animals other than freshwater crayfish, but the Chinese mitten crab,  Eriochier chinensis,  was susceptible to infection with A. astaci in an experimental study.

Of the commercial crayfish species in Australia, the Red Claw Crayfish (Cherax quadricarinatus) and the yabby (Cherax destructor) have been tested and are susceptible to the disease, but there are no published reports of the susceptibility of marron (Cherax tenuimanus). Only a few Australian species of crayfish have been experimentally challenged with crayfish plague, but it is safe to assume that all Australian freshwater crayfish may be highly susceptible to infection. The susceptibility of many freshwater decapods to infection with  A. astaci is unknown. Consequently, the likelihood of animals such as freshwater crabs and  shrimp in Australia becoming carriers or developing clinical disease following infection with A. astaci in the wild is also unknown.

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