Physiological and biochemical responses of Zhikong scallop, Chlamys farreri, to different thermal stressors

Water temperature is a significant environmental stressor that affects physiology and biochemical activities of bivalves. Here, temporal variations in physiological and biochemical parameters of Zhikong scallop, Chlamys farreri, under three water temperature treatments were investigated. For the first treatment, scallops were transferred from rearing temperature (15 degrees C, control temperature) to 5, 10, 20 and 25 degrees C, respectively. The second group of scallops was gradually acclimated to above experimental temperatures at a rate of 1-2 degrees C day(-1). The third group was transferred directly between 15 and 7 degrees C every 12h and for six times. Results showed that significantly higher oxygen consumption and ammonia-N excretion together with a significant lower ingestion rate was observed for the acute temperature change treatment compared to those in the equivalent gradual temperature variation treatment (P<0.05). In acute temperature change treatment, hepatopancreas antioxidant enzyme activities, that is, superoxide dismutase (SOD) and catalase (CAT), immune enzyme activities, that is, acid phosphatase (ACP) and lysozyme (LSZ), and heat-shock protein 70 gene (Hsp70) expression levels of scallops increased substantially within 48h. Significant increases in SOD, CAT, ACP and LSZ activities, and malondialdehyde content occurred under exposure to fluctuating temperatures (P<0.01). Gill and hepatopancreatic Hsp70 expression levels also increased significantly in response to water temperature fluctuations (P<0.05). The study provides basic knowledge about thermal stress in Zhikong scallop and may contribute to the management of scallop mortalities.