Psorospermium spp. (Protozoan Disease) of Australian Crayfish

Category

Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Psorospermium sp. of Australian crayfish, Protozoan disease.

Scientific name or taxonomic affiliation

Psorospermium sp. probably more than one species (taxonomic affinities of Psorospermium is under review).

Geographic distribution

Australia

Host species

Cherax tenuimanus, Cherax quadricarinatus, and Cherax quinquicarinatus. Other species of Psorospermium occur in various species of crayfish in North America and Europe.

Impact on the host

Amoeba-like and spore-like stages invade crayfish tissues with no evidence of pathogenicity. Infection appears to be cumulative over time because larger and presumably older C. quadricarinatus had heavier infections than smaller ones.

Diagnostic techniques

Gross Observations: Infected animals may show characteristic orange spots on the carapace. Some haemocytic encapsulation observed; melanization rare.

Squash Preparations: Large ovoid spores (40-55 × 94-100 µm) with multi-layered refractive cell walls (6-8 µm thick). Spores are usually located in connective tissue, particularly in the gills and neural tissues and occasionally the ovary membranes, cardiac and skeletal muscle of C. quadricarinatus in northern Queensland (Herbert 1987). Spore of Psorospermium sp. in C. tenuimanus from Western Australia were of even breadth with wall joints only seen at the middle of the spore and occurring within a ridge in the cell wall (Henttonen et al. 1997). May show other thin walled forms. Spores persist in dead crayfish for up to three days and may withstand desiccation.

Histology: The outermost layer of the multilayered wall is thin and amorphous and does not stain readily and the next layer is composed of irregular thick plates that are strongly eosinophilic when stained with haematoxylin and eosin stain. The Australian form differs from Psorospermium spp. described in Europe and North America in having two plates that join at the centre of the spore to create a central circular ridge (Edgerton et al 2002).

Methods of control

Methods of transmission are not understood. No known methods of control.

References

Aiken, D. 1989. Marron fungus? The author responds. World Aquaculture 20: 6-7.

Edgerton, B.F. and L. Owens. 1999. Histopathological surveys of the redclaw freshwater crayfish, Cherax quadricrinatus, in Australia. Aquaculture 180: 23-40.

Edgerton, B.F., L.H. Evans, F.J. Stephens and R.M. Overstreet. 2002. Synopsis of freshwater crayfish diseases and commensal organisms. Aquaculture 206: 57-135.

Evans, L.H. and B.F. Edgerton. 2002. Pathogens, parasites and commensals; Chapter 10. In: Holdich, D.M. (ed.) Biology of Freshwater Crayfish. Blackwell Sciences Ltd., Oxford, England. pp. 377-438.

Henttonen, P., J.V. Huner, P. Rata and O.V. Lindqvist. 1997. A comparison of the known life forms of Psorospermium spp. in freshwater crayfish (Arthropoda, decapoda) with emphasis on Astacus astacus L. (Astacidae) and Procambarus clarkii (Girard) (Cambaridae). Aquaculture 149: 15-30.

Herbert, B. 1987. Notes on diseases and epibionts of Cherax quadricarinatus and C. tenuimanus (Decapoda: Parastacidae). Aquaculture 64: 165-173.

Citation Information

Bower, S.M. (2006): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Psorospermium spp. (Protozoan Disease) of Australian Crayfish.

Date last revised: June 2006
Comments to Susan Bower

Date modified: