Abstract:In this study,the alterations of some typical hematoimmunological parameters in the swimming crab Portunus trituberculatus infected with low dose Vibrio alginolyticus were investigated.Healthy crabs with an average weight of(162±26)g were divided randomly into injected and control groups.Each crab was injected with 200 μL(2.4×107 CFU/mL)V.alginolyticus in injected group,and with 200 μL 0.85% sterile saline solution in control group.Then haemolymph samples were drawn from each crab at hours 0,24,48,72 and 96 post injection for testing hematoimmunological parameters including total hemocyte count(THC),proportion of large granular cells,total serum protein concentration,acid phosphatase(ACP),alkaline phosphatase(AKP),nitric oxide(NO)and inducible nitric oxide synthase(iNOS).THC of injected crabs was significantly 36% lower than in control group and touched the bottom post injection 24 h(P<0.05).Also,in injected groups,the proportion of large granular cells increased significantly at 24 h and 48 h(P<0.05),and returned to the same level at 72 h and 96 h.Noticeably,there was no significant difference in the injected and control groups in PC,although the numerical value of injected group waved during the test(lower at 24 h,48 h and higher at 72 h,96 h than control group).The ACP activity,after injection,increased very significantly at 24 h,48 h(P<0.01)and 72 h(P<0.05),then decreased to the control level at 96 h.The AKP activity increased gradually after injection,and noticeably,there was no significant difference with control group until at 48 h and 72 h(P<0.05),then decreased to the control level at 96 h.The NO concentration and iNOS activity of injected group shared the same pronounced increasing,there was no significant difference with control group until 72 h(P<0.01 for NO and P<0.05 for iNOS)and 96 h(P<0.01 for NO and iNOS),especially,the NO concentration in injected group was three times higher than that in control group at 96 h.All the results indicated hematoimmunological parameters of P.trituberculatus did play an important role in confronting the V.alginolyticus’s infection.