Effects of low salinity stress on immune response and evaluating indicators of the swimming crab Portunus trituberculatus

The purpose of the present study was to investigate the effects of salinity stress on immune responses and evaluating indicators in swimming crab Portunus trituberculatus. The crabs (150 ± 8.5 g in body weight) were exposed to different salinities as 21, 26 and 31‰ (control) for 6 days. The results showed the total haemocyte counts (THC) and prophenoloxidase (proPO) activity in the haemocytes decreased significantly in the treatment groups after 6 hr, and reached the lowest levels at 12 hr. The phenoloxidase (PO) activity in the plasma increased significantly and peaked at 12 hr, then recovered to control level after 24 hr. The phagocytic per cent of haemocyte, antibacterial and bacteriolytic activities in the plasma decreased significantly in the treatment groups, and reached the lowest level at 12 hr, then recovered to control level after 72 hr. The dopamine (DA) and 5-hydroxytryptamine (5-HT) contents in the plasma increased significantly and peaked at 12 hr, then recovered to control level, while the noradrenaline (NE) content in the plasma had no significant change throughout the duration of the experiment. The DA and 5-HT receptors were significantly up-regulated in the treatment groups. The highest value of mRNA expression of DA and 5-HT receptors occurred at 12 hr and recovered to control level after 24 hr. In addition, the cAMP and protein kinase A (PKA) contents in the haemocytes increased significantly and peaked at 12 hr, then recovered to control level after 72 hr. The phospholipase C (PLC) and protein kinase C (PKC) contents in the haemocytes increased significantly and peaked at 12 hr, then resumed to control level after 24 hr. These results speculated that biogenic amine (DA and 5-HT) is likely to play an important role in immune modulation via cAMP/PKA signalling pathway or PLC/PKC signalling pathway when P. trituberculatus is exposed to low salinity and these results will provide scientific data for immune evaluation.