Growth performances in cupped oysters (Crassostrea gigas) during pre-fattening stages in the middle Adriatic Sea: Influence of pathogens and environmental factors

In the last decades, demand for bivalves has significantly increased substantially worldwide. In the Adriatic Sea, offshore bivalve molluscs farming is almost entirely based on mussel farming although some companies started to diversify their production. Growth performance and interaction between host, pathogens and environmental factors were analyzed in different batches of cupped oysters (Crassostrea gigas), during the years 2018 and 2019. 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. 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. In order to maximize production and the profitability of the farm, the use of new locations for product finishing could be suggested.