Boys, C.A., Rowland, S.J., Gabor, M., Gabor, L., Marsh, I.B., Hum, S. and Callinan, R.B., (2012) Emergence of Epizootic Ulcerative Syndrome in native fish of the Murray-Darling river system, Australia: Hosts, distribution and possible vectors. PLoS ONE 7(4): e35568.  doi:10.1371/journal.pone.0035568

Summary

There are few records and little is known of the infectious diseases of fish in the Murray-Darling River System (MDRS), Australia. In June 2010, bony herring (Nematalosa erebi), golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii) and spangled perch (Leiopotherapon unicolour) with lesions or severe ulcers were sampled from a 200 km stretch of the Barwon-Darling River. Lab tests confirmed infection by the fungus-like pathogen Aphanomyces invadans and the reportable disease Epizootic Ulcerative Syndrome (EUS). Apart from one record of bony herring from the Darling River in 2008, EUS has been recorded in the wild only from coastal drainages in eastern, northern and Western Australia. This study confirms the presence of A. invadans in the MDRS, and is the first report of EUS in golden perch, Murray cod and spangled perch. The lack of previous cases, the large number of new hosts, the geographic extent and prevalence of this disease, the severity of ulceration and large number of individuals affected suggest a relatively recent invasion by A. invadans. An alternative “Perfect Storm” hypothesis is discussed whereby A. invadans is endemic to the MDRS, but in the past environmental conditions have not favoured an outbreak. Whilst this hypothesis is not favoured, low water temperatures (12.7° – 16.3°C) and high flows may have predisposed fish to infection in 2008 and 2010. Translocation of fish, migratory birds, boats and fishing equipment are potential vectors for the movement of A. invadans from coastal drainages to the MDRS. Recommendations are made for further surveillance, research and biosecurity.