| In this paper, juvenile Amur sturgeon was targeted and set different levels of salinity, pH and capture time, we investigated the regulations of acute salinity stress, chronic salinity, pH and capture stress on growth performance and physiological system of Amur sturgeon, Acipenser schrenckii. The short-term and long-term effects of stress on blood physiological, biochemical, growth rate, immunity ability were studied.1. The effect of acute salinity stress on physiological index and immune enzyme activities of Acipenser schrenckiiExperiments were conducted to investigate the plasma cortisol, metabolism responds of juvenile Acipenser schrenckii to ambient salinity mutant, plasma Na~+, Cl~- and K~+, gill Na~+/K~+-ATPase , SOD and CAT activities were measured with the aims to explore the mechanism osmoregulation and immunity of A.schrenckii. The results showed that the plasma cortisol, glucose and lactate levels of the fish in salinity stress increased firstly, and then recovered to the normal level in 24,48,96 h, respectively, as those of the control groups. Plasma Na~+ concentration increased with the ambient salinity and the time stressed, while Cl~- concentration of fish at both 15 and 22 ppt increased firstly and then decreased, and significantly differences were not observed in K~+concentration of fish of different treatments. Salinity mutant led to plasma osmolarity increase. The Na~+/K~+-ATPase activity of fish in salinity stress showed the trend of increasing firstly to its peak at 12 h, and then decreased, however, the activity of Na~+/K~+-ATPase kept at a higher lever than that of the control group. In 0.5-24 h and 96 h, 15, 22 salinity group of SOD activity were significantly higher than control group. Compared with the control group, CAT activity of salinity 15 was significantly higher than control group except for 12 h; salinity 22 at the beginning of a slight decrease, with the control group were not significantly different.In conclusion, the plasma cortisol content was more sensitive than the plasma glucose and lactate content to the ambient salinity change, and changed with the salinity change in time. Moreover, the juveniles of A.schrenckii have strong adapbility to ambient salinity mutant, and they can adapt themselves with 96 h to certain degree by endocritic and metabolism adjust . Meanwhile, salinity mutations lead to massive fish active oxygen free radicals, SOD, CAT activity increased to remove reactive oxygen free radicals, thereby protecting cells from the body harm.2. Combined effect of salinity and pH on growth and immunity ability of A.schrenckiiThe effect of salinity (0, 10 and 18) and pH(6.0～6.5, 7.0～7.5 and 8.0～8.5) on growth and immunity ability of A.schrenckii was discussed in this part. Growth index measured include survival rate SR, the average growth rate AGR, specific growth rate SGR, liver system for HSI, Feeding rate FR and food conversion ratio FCR; several non-specific immune factors include lysozyme, C3 and C4 activity.The results showed that the salinity and pH on the SR, FCR and FR had interaction. The sequence from high to low of SR was freshwater control group, salinity 10 and 18 group, freshwater group, the AGR group of salinity 10 and 18 had no significant difference. SGR, HSI and AGR had a similar trend: freshwater group, salinity 10 and 18 showed no significant differences. FCR of salinity 10 was significantly lower than salinity 18 group , while FR was on the contrary. The effect of pH on A.schrenckii was not significant.Combined effect of salinity and pH on the activity of lysozyme had interaction. The lysozyme activity of salinity 10 was significantly higher than that of freshwater and salinity 18 group, there were no difference between freshwater and salinity 18 group. Salinity and pH on the activity of C3 had no interaction. Under pH6.0-6.5 and pH8.0-8.5 conditions, the C3 has trend of decrease from freshwater group, salinity group 10 and 18, and salinity 18 was significantly lower than the group of freshwater and salinity 10.The results suggested that the Amur sturgeon was most suitable for the growth environment in salinity 10 and neutral pH. Due to the existence of interaction, alkaline pH and salinity 18 provided poor growth environment for A.schrenckii, but A.schrenckii can still maintain a certain growth rate. The increase of non-specific immune factors' activity reflect the body had a protective mechanism in a period after the stress in order to maintain its balance of the body to overcome stress. The decrease of the activity in salinity 18 group may indicate that high salinity environment had suppressed fish immune system somewhat.3. The effect of salinity and capture stress on blood physiological, biochemical and non-specific immune factors of A.schrenckiiAcute capture stress and recovery on the Amur sturgeon under freshwater and salinity 10 respectively trained 60d was studied. We investigated plasma cortisol level, physiological and biochemical parameters of blood and non-specific immune factors. The results showed at 1～2 and 4～5min capture, salinity 0 and 10 group of cortisol level were significantly higher. With the time past, cortisol level within 24 h was reinstated to the initial level. Glucose of Amur sturgeon in freshwater and salinity 10 had no significant impact. The changes of Blood TP, LDH, ALT, AKP, bilirubin and cholesterol level in freshwater and salinity group were unanimous, which were increased until reach to the highest value at capture 4～5min, and then recover within 24 hours. AST and UREA showed an average decline after the upward at first and downward trend in the recovery phase. Their concentrations were slightly lower than the initial value. Capture stress can lead to lysozyme, C3 and C4 activities increased in different degrees, but 24 h recovered initial value.In Conclusion, there were no significant difference between freshwater and saltwater on physiological and biochemical indicators of of A.schrenckii under capture stress , acute stress on A.schrenckii physiological and biochemical indicators and the non-specific immune factors varied in some degrees. This depends on the time of stress and physiological conditions of fish itself, but within 24 hours can restore the initial basic level. This shows that juvenile sturgeon body has a strong immune system and the ability to regulate the balance. |
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