In order to explore how to reduce the amount of fish meal while maintaining the good growth performance and stress resistance of Litopenaeus vannamei, in this study, the basic diet containing 10% fish meal was added with 0% (A), 2.5% (B), 3.5% (C), 4.5% (D) and 5.5% (E) of proteolytic soybean meal (PSM) to produce five groups of isonitrogonous isoenergetic feed. L.vannamei juveniles with initial body weight of (0.45+0.02) g were fed for 8 weeks. Then the growth performance and stress resistance of L.vannamei were assessed. The results showed that the final body weight of shrimps in each experimental group ranged from 14.65 to 15.38 g/individual after 8-week culture experiment, and there were no significant differences in weight gain, survival rate and feed coefficient among the groups. The crude protein content of shrimp muscle in group A was significantly lower than those in other experimental groups. The crude fat contents of shrimp muscle in group C, D and E were significantly higher than that in group A. There was no significant differences in ash and moisture content among other groups. The activities of hepatopancreas protease, hepatopancreas amylase, hepatopancreas lipase, serum lysozyme and serum T-SOD in shrimp fed D and E diets were significantly higher than that in group A. The serum MDA content in group A was significantly higher thsan those in other groups. In the stress test of artificial acute infection with high dose Vibrio Parahaemolyticus, the cumulative mortality of shrimp in group A at 48 h and 60 h post Vibrio infection was significantly higher than that in group D. The expression levels of Toll receptor, immune deficiency (IMD) and Lysozyme were detected in shrimp gill tissues after artificial acute infection with low dose V.parahaemolyticus. The results showed that the peak values of Toll receptor, IMD and Lysozyme mRNA expression appeared in group C at 24 h post infection, group B at 42 h post infection and group D at 24 h post infection, respectively.
To sum up: in the feed containing 10% fish meal, the effect of proteolytic soybean meal less than 5.5% on the growth performance of L.vannamei is not significant. The dietary proteolytic soybean meal could significantly increase the crude protein content and crude fat content in muscle and decrease the MDA content in shrimp serum. Under the experimental conditions, the dietary proteolytic soybean meal significantly changes the resistance of L.vannamei to Vibrio and the temporal and spatial expression of immune-related genes. Using 4.5% proteolytic soybean meal in feed containing 10% fish meal can obtain the best anti-Vibrio ability of cultured L.vannamei.
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