Acta Hydrobiologica Sinica (水生生物学报) 2012/36:6 PP.1056-1062
Most of the decapod species of crustacean have comprehensive capacity of osmoregulation, and they can adapt to relative wide ambient salinity range. It is important to understand the underlying mechanisms of their comprehensive adaptability to salinity change because this knowledge is helpful for inland culturing of marine species. As a euryhaline crustacean, the Chinese mitten crab, Eriocheir sinensis, has been well studied in many aspects related to their physiological responses to salinity change, and many useful literature findings have been accumulated. Therefore, E. sinensis can be considered as an animal model for studying osmoregulation mechanism of the decapod species. However, the roles of nutrients in osmoregulation of E. sinensis are still limited. In this paper, male E. sinensis in freshwater (0.3‰) were transferred directly into waters at salinity values of 16‰ and 30‰, respectively, and the crabs kept at fresh water served as the control. Each treatment has three replicates. The soluble protein in haemolymph and hepatopancreas, hemocyanin, haemolymph glucose and hepatopancreas glycogen at 0h, 6h, 12h, 24h, 48h, 72h and 96h of E. sinensis at different salinities were determined. Soluble protein of haemolymph and hepatopancreas were measured with a Folin reagent based on a standard curve using bovine serum albumin as the standard protein. Hemocyanin was assayed using an ultraviolet absorption methods at 335 nm and calculated according to Nickerson =2.83. Haemolymph glucose was assayed using glucose oxidase-peroxide enzyme (GOD-POD) method. Hepatopancreas glycogen was measured using the anthrone colorimetry method. The results showed that the crabs at salinity 16‰ and 30‰ had significantly lower soluble protein content of hepatopancreas than those at fresh water (P<0.05) when crabs had encountered salt water for 12h—96h, and the soluble protein content of haemolymph decreased significantly from 6h to 48h, and then increased at 72h. The hemocyanin content showed a significantly decreasing trend from 0h to 24h, and then it increased after 48h. Hepatopancreas glycogen contents at salinity 16‰ and 30‰ were significantly lower than those at fresh water (P<0.05) from 6h to 96h, while no significant differences were observed between crabs in waters with salinity 16‰ and 30‰ (P>0.05). Haemolymph glucose content at 16‰ reduced significantly (P<0.05) from 24h to 48h, and gradually recovered up at 72h, but it showed a significantly decreasing trend from 6h to 12h at salinity 30‰, and then gradually increased after 24h. All these results indicated that E. sinensis could produce physiological and biochemical adaptation to maintain a stable osmotic pressure during acute salinity stress. Carbohydrate and protein play important roles in the osmoregulation of crustaceans. E. sinensis could use carbohydrate first to provide energy under acute salinity stress. The higher the salinity, the faster the haemolymph glucose was consumed, and it also recovered more quickly. This observation suggested that carbohydrate could be a direct source in osmoregulation. The crabs may use protein to maintain the balance of osmotic pressure under high salinity by metabolizing the protein into free amino acids. Beside providing free amino acids, hemocyanin also can carry oxygen to meet the needs for physiological activities. Therefore, more attention should be paid to carbohydrate and protein supplied under salinity stress. The ratio of free amino acids maintaining the balance of osmotic pressure and supplying energy by oxidation and the utilization of lipid in osmoregulation require further study. Since the lipid contents in haemolymph and hepatopancreas were not determined in this study, the role of body lipid in E. sinensis was not discussed here and should be further examined.