Infection dynamics of Bonamia exitiosa on intertidal Ostrea angasi farms.

Abstract

Bonamia spp. cause epizootics in oysters worldwide. In southern Australia, Bonamiaexitiosa Hine, Cochennac and Berthe, 2001 threatens aquaculture of Ostrea angasi Sowerby, 1871. Bonamiaspp. infections can display strong seasonality, but seasonal dynamics of B.exitiosa-O.angasi are unknown. Ostrea angasi naïve to B.exitiosa infection were stocked onto farms in three growing regions, and B.exitiosa was monitored seasonally for oneyear. Environmental parameters we measured did not correlate with B.exitiosa prevalence or infection intensities. Extreme temperatures suggest O.angasi culture systems need development. Bonamiaexitiosa prevalence increased over time. After threemonths, O.angasi had B.exitiosa prevalence of 0.08-0.4, and after oneyear, the prevalence was 0.57-0.88. At some sites, O.angasi had >0.5 B.exitiosa prevalence in >6months, but at other sites, >9months passed before prevalence was >0.5. Bonamia exitiosa infection intensities were low with no seasonal pattern but were affected by the interaction of site, season and oyster meat:shell ratio. Understanding infection and initiating a breeding programme for resistance would provide benefits for O.angasi industry expansion.