Risk factors for POMS in Tasmania 2016

The first outbreak of disease due to OsHV-1 occurred in Tasmania in January 2016. We investigated the factors that were associated with mortality on affected farms.

de Kantzow M, Hick P, Dhand NK and Whittington RJ (2017). Risk factors for mortality during the first occurrence of Pacific Oyster Mortality Syndrome due to Ostreid herpesvirus-1 in Tasmania, 2016. Aquaculture 468: 328-336.

Summary: The microvariant genotype of Ostreid herpes virus 1 (OsHV-1 μVar) has caused repeated seasonal outbreaks of mass mortality in Pacific oyster (Crassostrea gigas) populations in Europe, New Zealand and in New South Wales, Australia. The first occurrence of OsHV-1 related mortality in Tasmania, Australia was in January 2016; mortality was documented and multivariable logistic regression analysiswas undertaken to examine risk factors. Overall mortalitywas 78% but varied from 37%92% across 6 farms and between 96% (020mmlength) and 33% (61115 mm) across size classes. The odds of mortality were 3.2 to 3.8 times greater for baskets containing oysters with an average shell length 40mmcompared to thosewith an average 61mm. Generally, the greater the time on farm the lower the mortality, consistent with the increasing age and size of the oysters. The effect of stocking density on mortality changed with increasing time on farm (age). The standard density produced lower mortality than high or low stocking density particularly for spat. Mortality was nearly twice as likely when oysters were handled for routine husbandry in the 7 days prior to the outbreak compared to not handled. Ploidy and hatchery of origin did not alter the disease outcome. The variation in mortality with husbandry requires further investigation to determine if it can be exploited to help maintain productivity. Describing the impact of OsHV-1 in new environments and identifying the association between farm management and mortality is important to develop effective disease control measures.

If you would like a copy of the scientific paper please send a request by e-mail to: paul.hick@sydney.edu.au