Publication Abstract

Characterisation of a Rosette agent (Sphaerothecum destruens) from sunbleak (Leucaspius delineatus) in the UK.

R. Paley*, D. Andreou, P.Martin*, D. Stone*, K. Bateman*, S. Irving* and S. Feist*. 13th international conference of the EAFP, Grado, Italy

Sunbleak (Leucaspius delineatus), a cyprinid fish native to continental Europe is experiencing population decline which appears to be linked to the spread of the invasive Asian cyprinid (Pseudorasbora parva). Species interaction studies showed inhibition of spawning, wasting then death in L. delineatus cohabited with P. parva, or exposed to their holding water (Gozlan et al. 2005). Histological examination lead to the identification of an intracellular parasite, similar to the freshwater Mesomycetozoean parasite, Rosette agent (Sphaerothecum destruens) that infects salmonids in the USA. Subsequent PCR and sequence analysis of a partial 18S rRNA gene demonstrated 100% homology. S. destruens is capable of survival in fish in the marine environment and has been associated with sporadic severe infectious disease (occasionally mortalities up to 90%) of cage-reared Chinook salmon (Oncorhynchus tshawytscha) in North America (Elston et al. 1986; Arkush et al. 1998) and in farmed Atlantic salmon (Salmo salar) in freshwater in California (Hedrick et al. 1989). In the US the disease is usually chronic and does not appear to impair spawning of infected fish.  Information on the impact on wild stocks is extremely limited.   This is the first identification of this parasite in the UK and from a cyprinid. Given the potential for causing severe disease we have developed cell-culture of the sunbleak rosette agent for use in pathogenicity studies. Sunbleak rosette agent spores are infective to EPC, CHSE and FHM cells replicating most rapidly in EPC cells. Spores can be induced to zoosporulate in water forming motile uni-flagellated zoospores in a temperature dependant manner. Challenge experiments with spores and zoospores in salmon and sunbleak are ongoing; characterisation and initial pathogenicity studies will be described.

Arkush, K.D., Frasca, S. (Jr) and Hedrick R.P. (1998) Pathology associated with the Rosette agent, a systemic protest infecting salmonid fishes. J. Aquat. Anim. Health. 10:1-11

Elston R.A., Harrell, L. and Wilkinson M.T. (1986) Isolation and in vitro characterization of Chinook Salmon (Oncorhynchus tshawytscha) Rosette agent. Aquaculture. 56:1-21

Gozlan, R.E., St-Hilaire, S., Feist, S.W., Martin, P. and Kent, M.L. (2005) Biodiversity: disease threat to European fish. Nature. 2005 435(7045):1046. 

Hedrick, R.P., Friedman, C.S. and Modin, J. (1989) Systemic infection in Atlantic Salmon Salmo salar with a Dermocystidium-like species. Dis. Aquat. Org. 7:171-177