Effect of zinc sacrificial anode degradation on the defence system of the Pacific oyster, Crassostrea gigas: Chronic and acute exposures

► Crassostrea gigas were exposed to zinc released from a sacrificial anode. ► Two types of experiments were performed: long- and short-term laboratory tests. ► Immune parameters and mRNA expression of genes implied in detoxification were analysed. ► Oysters were affected by an acute Zn concentration and moderately impacted by a mild one. Two types of exposures were performed to assess the effects of zinc released from sacrificial anode degradation: a chronic exposure, in which oysters were exposed to 0.53±0.04mgZnL−1 for 10weeks, and an acute exposure, where oysters were exposed to 10.2±1.2mgZnL−1 for 1week. At the end of the acute exposure experiment, 81.8% mortality was recorded. In contrast, no mortality was detected after 10weeks exposure. Moreover, all of the immune system biomarkers studied, except the number of circulating haemocytes, were stimulated by a moderate level of zinc and inhibited by a high level. Our exposure conditions did not induce SOD or MXR mRNA expression in gills and digestive gland. However, an increase of MT mRNA is observed in these tissues. The results indicate that oysters are sensitive to acute zinc toxicity but are only moderately affected by a mild zinc concentration.