Spawning-dependent stress response to food deprivation in Pacific oyster Crassostrea gigas

This study investigated the impact of spawning on metabolic and immunological responses in Pacific oysters Crassostrea gigas under food deprivation. Both pre- and post-spawning oysters were deprived of food for 80 days and then refed for 52 days. Overall mortality was less than 4%, but the condition index was significantly reduced by food deprivation and spawning. Mantle glycogen of post-spawning oysters was less than pre-spawning oysters and was further depleted with reduction of adductor glycogen during food deprivation. Under food deprivation, mantle and gill proteins in pre- and post-spawning oysters were also reduced and maintained at a low level until feeding recommenced. Pre-spawning oysters exhibited strong metabolic resilience to food deprivation as indicated by faster glycogen and protein recovery than post-spawning oysters upon refeeding. The results of hemocyte phagocytosis and hemolymph antimicrobial activity also demonstrated that post-spawning oysters had low immune resilience under food deprivation. This study indicates that food deprivation impedes metabolic and immunological activities in oysters, resulting in a prolonged post-spawning recovery and low metabolic and immune capacity. This finding contributes to our understanding of the factors contributing to oyster mortality in areas with low food supply.