Effects of salinity on feeding behavior and growth characteristics of swimming crab Portunus trituberculatus

Effects of salinity on feeding behavior and growth characteristics of juvenile and adult swimming crab Portunus trituberculatus were investigated, based on the behavior experiment using 5 salinity levels, i.e., 5, 10, 20, 30, and 40. The results showed, at low salinity of 5, the juvenile almost rested in a sand hole(Rh) about 0.5 cm depth; at high salinity of 40, the juvenile dug a shallow sand hole(about 0.1 cm) which just covered its carapace; at salinities of 10, 20 and 30, the period of outside-sand was longer for feeding and activity than at other salinities. There were 2 or 3 feeding times and each lasted 30-60 min, total fed period was about 30 min to 3 hours. Compared with juvenile, feeding time for adult crab was once to twice, and other activity rhythms were not different between juvenile and adult. Furthermore, at salinities of 10-40, the average food intake per day of juvenile was 0.0999 g·g?1, and had a biggest value of 0.1974 g·g?1 at salinity of 20. It meant the suitable growth condition of salinity for juvenile was 10-40, and 20 was the optimal salinity. It also could be proven by moulting rate of juvenile crab during the experiment; all juvenile moulted at salinity of 20, and 2/3 juveniles at 30 and 40, only 1/3 juveniles at 10, and no crabs at 5, respectively.