Immune Response of the Ridgetail White Prawn Exopalaemon carinicauda After Exposure to the Dinoflagellate Prorocentrum minimum

The dinoflagellate Prorocentrum minimum is known to affect the normal physiological function of Exopalaemon carinicauda by inducing oxidative stress, apoptosis, and cellular injury. To study the effects of P. minimum on the immune defense system of shrimp, E. carinicauda were exposed to 5 x 10(3) cells mL(-1) and 5 x 10(4) cells mL(-1) of P. minimum for 336 h in treatment groups, while E. carinicauda cultured in filtered seawater was employed as control. The total hemocyte counts (THC), hemocyanin concentration (HEM), and the activity of alkaline phosphatase (AKP) in hemolymph serum, as well as expressions of six immunity-related genes in hemocytes, hepatopancreases and gills were determined. The exposure of P. minimum significantly reduced the THC, HEM concentration and AKP activity in hemolymph serum. Immunity-related genes expressed differently in hemocytes, hepatopancreases and gills. Compared with the control group, the expressions of Crustin and proPO in hemocytes were significantly up-regulated in the treatment groups, while the up-regulated expressions of LGBP, Lysozyme and Serpin were only found in the group exposed to 5 x 10(4) cells mL(-1) of P. minimum. In the gills of E. carinicauda exposed to P. minimum, the down-regulation of ALF, proPO and Serpin, up-regulation of LGBP and Lysozyme, as well as unaffected Crustin were observed. In hepatopancreases, the up-regulated expressions of LGBP, Crustin, Lysozyme, Serpin and proPO (only in 5 x 10(3) cells mL(-1) of P. minimum group) were found in the treatment groups. After exposure to P. minimum for 336 h, shrimps were injected with Vibrio parahaemolyticus and WSSV. The results showed that the mortality rates of shrimp in the treatment groups were significantly increased with a dose-dependent effect, which suggests that exposure to P. minimum may reduce the immunity of E. carinicauda. The research indicates that hemocytes and hepatopancreases play important roles in protecting the shrimp immune response to harmful algae, while the protection effect of hemolymph serum and gills may be suppressed. Since the exposure to P. minimum depressed the immunity of E. carinicauda, further studies are needed to confirm whether the presence of the algae will affect the susceptibility of shrimp to pathogens.