Physiological comparisons of Pacific cupped oysters at different levels of ploidy and selection to OsHV-1 tolerance

The production and supply of triploid oysters Crassostrea gigas has become an increasingly frequent activity in aquaculture companies to satisfy the growing demand of growers. These triploid oysters are usually obtained by crossing male tetraploid oysters with female diploid oysters. Furthermore, studies have shown that it is possible to select oysters for better resistance to infection by OsHV-1 and they are currently produced by commercial hatcheries in France. The effects of ploidy and selection on the physiological functioning of the Pacific cupped oyster are still relatively unknown, especially in tetraploid animals selected for better resistance to infection by OsHV-1. In the framework of sustainable domestication, and by taking into account the natural habitat, it has become necessary to shed more light on the subject. Faced by this lack of knowledge, a physiological study of respiration and clearance rate was performed on 6 stocks of C. gigas oysters whose levels of ploidy (2n, 3n and 4n) and sensitivity to OsHV-1 resistance (selected and non-selected) were different. The experiments were performed in controlled and reproducible habitats where OsHV-1 is absent. The physiological results showed: i) an absence of interaction between ploidy levels and selection; ii) families showed no significant difference as a function of the level of selection to OsHV-1 tolerance; and iii) significant differences in clearance rate and daily weight growth as a function of the oysters' ploidy level. In particular, the results revealed that the clearance rate of tetraploids was lower than that of diploid and triploid oysters with a growth rate equal to that of triploids and higher than diploids. Additional studies are envisaged in the discussion to better understand these results. •Production of triploid oysters has become an increasing activity in aquaculture companies to satisfy the demand of growers.•Effects of ploidy and selection for resistance to pathogens on the physiology of oysters are misunderstood.•The interest of this study is to verify the effects of selection and ploidy on the physiologyl of cultivated oysters.