Effects of 10 salinity to the plasma osmotic pressure, cortisol, glucose and liver glycogen in Colilia nasus stressed during loading and transportation

In this study, we selected Coilia nasus from the Yangtze River with the average body length of (13.580.23) cm and the average body weight of (8.550.39) g as the experimental subjects, and we simulated the conditions during transportation for the experiments. These fish were divided into the normal stress group and the salt stress group (with 10 salinity), and there were three parallel repeats in each group. After the 8h transportation the survivors were put back into the original breeding pools. Samples from both groups were collected at certain time points -before loading (BL), after loading (AL), 2h, 4h, 6h, and 8h after the beginning of transportation, 24h recovery, and 96h recovery. We tested the plasma osmotic pressure, cortisol, glucose and the liver glycogen of these samples. The result showed that after the 96h recovery, the survival rates of the normal stress group and the salt stress group were 20% and 100% respectively. The blood osmotic pressure was reduced in the normal stress group after transportation. In contrast it was significantly elevated in the salt stress group, and reached to the peak value (0.3480.002) mOsm/kg 8h after the beginning of transportation. The plasma cortisol rapidly climbed to the peak 2h after the beginning of transportation in the normal stress group, whereas, it reached to the peak (574.7164.75) ng/mL 4h after the beginning of transportation in the salt stress group. The level of glucose in the normal stress group was significantly elevated after the transportation, but its change in the salt stress group was much milder and the concentration was stabilized 6h after the beginning of transportation. Moreover, the glucose concentration in the salt stress group was significantly lower than that in the normal stress group. The change in the liver glycogen was consistent with the change in glucose level, so we speculated that the increase in glucose resulted from the glycogenolysis of the liver glycogen. These results suggested that 10 salinity could significantly improve the level of plasma osmotic pressure, reduce the energy consumption of material, and avoid strong stress reactions such as walling and rawing, therefore effectively raise the survival rate.