High temperatures alter the patterns of growth and development and cause physiological and biochemical stresses in Chinese cyclina Cyclina sinensis

Prolonged high temperature is a critical environmental factor contributing to the mass mortality of clams in summer. We investigated the growth and development of Cyclina sinensis cultured at different temperatures (25, 28, 31, and 34 degrees C) and their physiological and biochemical responses following a long period of exposure. The mortality rates at 31 degrees C and 34 degrees C were significantly higher than at 25 degrees C and 28 degrees C after 48 d ( P < 0.05). The overall survival rates at 25 degrees C and 28 degrees C did not differ significantly from the control group (at natural seawater temperature), but were significantly lower at 31 degrees C and 34 degrees C ( P < 0.05). The growth parameters of C. sinensis in all of the experimental groups were significantly higher than in the control group ( P < 0.05), with the highest specific growth rate at 28 degrees C. The shell to soft tissue ratio was greatly increased in the 31 degrees C and 34 degrees C groups and was significantly higher than in the other groups after 32 d ( P < 0.05 ). The condition factor at 28 degrees C was significantly higher than in the other groups ( P < 0.05 ), and started to decline after 32 days at 31 degrees C and 34 degrees C. The hepatopancreatic and gonadotropic indexes were significantly lower at 31 degrees C and 34 degrees C than in the control group ( P < 0.05). Appropriate temperature rises increased the filtration rate and ingestion rate but these were clearly inhibited at 31 degrees C and 34 degrees C. The activities of superoxide dismutase, catalase, acid phosphatase (ACP), and lysozyme (LZM) were significantly reduced at 31 degrees C and 34 degrees C ( P < 0.05). The activities of ACP, LZM, amylase, and the proteases were significantly increased at 28 degrees C ( P < 0.05). Our study showed that high temperatures accelerate the growth of shells but inhibit the growth of soft tissues, negatively affecting the development, physiology, and biochemistry of C. sinensis . Cyclina sinensis demonstrates better overall performance at 28 degrees C, but aquaculture production would be severely affected if the temperature reaches, or exceeds 31 degrees C.