Effects of acute nitrite exposure on immunity indicators and HSP70 expression in chinese mitten-hand crab {Eriocheir sinensis)

Nitrite is an intermediate product either in the bacterial nitrification of ammonia, or in the bacterial denitrification of nitrate. The concentration of nitrite may reach 50 mg L ^-1 in intensive aquacultural systems due to an imbalance in biofilter resulting from overcrowding effect and poor water recirculation. High levels of nitrite in water were potential factors triggering stress on aquatic organisms. The sensitive indicators of stress evaluation for the Chinese mitten-hand crab Eriocheir sinensis were selected to investigate the effect of ambient nitrite on the immunity response. In this experiment, the juvenile crabs (mean weight: 3.25 g) were divided into four nitrite exposed groups (10, 20, 30 and 40 mg L ^-1 ambient nitrite concentrations) and control group. The total hemocyte counts (THC), superoxide dismutase (SOD) activity, malodiadehyde (MDA) level and HSP70 expression were measured after 3 h, 6 h, 1 d, and 2 d stress. The results were showed as follows: 1) After treated in low concentration (10 mg L ^-1) nitrite exposure, THC increased significantly at 3 h and SOD activity in hepatopancreas increased significantly at 3 h and 6 h compared with the control group, which indicated a poison-intoxication effect. 2) With time elapsing and ambient nitrite increasing, THC and SOD activity in hepatopancreas decreased while MDA level in hepatopancreas incread, which indicated accelebrating effect of lipid peroxidation by nitrite exposure. 3) HSP70 could be expressed at a low level in gills of crabs in the control group. The HSP70 expression reached a peak at 6 h stress when exposed in 10 and 20 mg L ^-1.nitrite and at 3 h stress when exposed to 30 and 40 mg L'1 nitrite. The maximum expression was positively correlated with the concentration of ambient nitrite. Therefore, nitrite stress played a mainly role in decreasing of immunity by accelerating lipid peroxidation. The level of MDA in hepatopancreas was an effective indicator and HSP70 expression in gills also could be an early indicator of nitrite stress.