Exploring correlations between spawning mediated response and summer mortality in Pacific oyster Crassostrea gigas

Pacific oyster, Crassostrea gigas, is one of the most important species for aquaculture and ecological indicators for environmental changes. However, mass summer mortality has become a widespread challenge to Pacific oyster aquaculture industry in recent decades. Due to the energy cost for gametogenesis, the reproductive season is considered a period of high risk for mortality events. This chapter reviews both immunity and energy metabolism in Pacific oysters, providing an appropriate approach to evaluate the integrative health condition in oysters, with a focus on the spawning-dependent stress response via comparison between pre- and post-spawning oysters under environmental stress. This review endeavor reflects the likely consequences of oyster spawning under food deprivation, heat shock and bacterial challenge and contributes to our understanding of the underlying mechanisms for oyster summer mortality. As oysters have already been used as important bioindicators in the environment and are representatives for intertidal populations, the implications of spawning impacts on resilience to environmental stress may be applicable to other compatible species in similar geographic distributions. By drawing on the broader literature from other commercial species, particularly clams, mussels, cockles and abalone, we synthesized the current evidence for spawning related immuosuppression contributing to epidemic disease and mortality in molluscs. This review provides insights into the understanding of global warming effects on ocean productivity in a world-wide aquaculture species whose reproduction is triggered by temperature increases.