Influence of environmental factors and pathogens on prefattening stages of cupped oysters Crassostrea gigas raised in the middle Adriatic Sea

In last decades, demand for bivalves has significantly increased almost worldwide. In the Adriatic Sea, offshore bivalve molluscs farming is almost entirely based on mussel farming although some companies started to diversify their production. The impact of environmental factors and host/pathogens interaction on growth performance and mortality of Cupped oysters (Crassostrea gigas) were analysed on different batches, during the years 2018 and 2019. Sea Surface Temperature and Chlorophyll-a measures were obtained from the database provided by Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard NASA’s Aqua satellite. Our results show a significant growth rate of the oysters reared in the Adriatic Sea, but an increase of mortality in summer months. Histological analysis does not show the presence of specific pathogens, recording only a strong positivity with immunohistochemistry for Vibrio spp. in summer 2018, but not in 2019. The research of OsHV-1 and V. aestuarianus shows negative results in all the time points, but we demonstrated that there was a combined effect of Sea Surface Temperature, Chlorophyll-a and Vibrio clade splendidus concentration on oysters’ mortality. Despite the high mortality and the resulting economic loss during the summer months, oysters farming seems to be a feasible activity in the Adriatic Sea. To maximize production and the profitability of the farm, new locations for product finishing could be suggested based on the findings of this study.