Physiological Responses of Sunray Surf Clam, Mactra chinensis in Low Salinities
Jun Hyung Ryu, Byung Hwa Min and Ki Tae Kim
Department of Marine Bio-Materials and Aquaculture, Pukyong National University, Busan 608-737, Korea Aquaculture Management Division, National Fisheries Research & Development Institute, Busan 619-705, Korea East Sea Fisheries Research Institute NIFS,
To investigate the tolerance of Sunray surf clam, Mactra chinensis in low salinities, survival and physiological responses related to osmoregulation of clams (60.2 ± 3.5 mm) were examined in 10, 20 and 30 psu at 15℃. The survival rate was 65.0% in 20 psu up to 216 h, while in 10 psu, severe mortality was recorded after 48 h and all died up to 96 h. Total hemocyte count (THC) was maintained a consistent level in 30 psu. While in 20 psu, it tended to decrease up to 24 h and afterwards, recovered gradually. In 10 psu, it was increased up to 6 h and tended to decrease later on. Osmolality of hemolymph followed the level of experimental water after 3 h 30 and 20 psu respectively, while in 10 psu, it did not completely follow the level of experimental water up to 48 h. Na+, Cl-, K+ and Ca of hemolymph showed the same as the result of osmolality. Glucose of hemolymph was significantly increased at 72 h in 20 psu. In 10 psu, it was significantly increased at 12 h first and sharply increased at 48 h. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) of hemolymph were significantly increased at 48 h in 10 psu simultaneously. Oxygen consumption and ammonia excretion were significantly decreased below 20 psu. Therefore, it is judged to be harmful on physiological activity of Mactra chinensis when be exposed to 20 psu over 72 h or to 10 psu over 12 h, respectively.
  
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