| Litopenaeus vannamei is one of the world's important farmed shrimp species for its fast growing and better environmental adaptability. However, the outbreaks of vibriosis such as acute hepatopancreatic necrosis disease and translucent post-larva disease had become one of the important constraints on the development of shrimp aquaculture industry around the world in recent years. Due to the negative consequences associated with the use of antibiotics to control bacterial diseases, the alternative technologies, such as increasing shrimp immunity, improving nutrition level of shrimp diets and the ecological environment of shrimp ponds by using probiotics have been developed. Being limited by the source and cost of fish meal, a large amount of vegetable protein was usually used as fish meal substitute in shrimp artificial feed , which is not only difficult to be digested and absorbed, but also can lead to nutritional antagonism. In order to improve the health status of aquaculture animals by feeding high quality feed , the technology of using fermented feed has been received extensive attention . Probiotic in fermented feed can produce exogenous cellulase, protease, amylase and other digestive enzymes in the digestive tract of farmed animals, which can improve the feed utilization rate, promote the growth performance and enhance immunity of shrimp. . In this study, in order to explore the application effects of shrimp feed fermented by different probiotic bacteria, probioticstrains including Bacillus subtilis, Saccharomyces cerevisiae and Lactobacillus acidophilus were used individually and in combination for the fermentation of commercial feed and fed to shrimp L. vannamei for 28 days. The survival rate, body length growth rate, specific growth rate and feed conversion rate of the shrimp were analyzed, and the density of Vibrio in vitro and in vivo as well as relevant immune indicators in the serum were analyzed. In addition, the concentrations of ammonia nitrogen and nitrite nitrogen in the water column were compared between the groups. The results showed that the survival rates of shrimp in fermented feed groups of B. subtilis, L. acidophilus and complex bacteria were 8.54%, 8.54% and 9.76% respectively, which were significantly higher than that of the control group(P<0.05) . The body length growth rates in groups of B. subtilis and L. acidophilus were significantly higher than that of the control group (P<0.05), while the feed conversion rate in group of L. acidophilus was significantly decreased compared with the control (P<0.05). There was not significant difference in specific growth rate of shrimp between experimental groups and the control group (P>0.05). Fermented feed could effect the composition of bacteria in hepatopancreas of shrimp. The density of Vibrio in the hepatopancreas of shrimp in each experimental group was significantly lower than that in the control group on days 14 and 21 of the experiment (P<0.05). The feeding of different fermented feed in short-term (within 14 d) had no significant effect on reducing the total density of Vibrio in the water body. However, the feeding of B. subtilis and L. acidophilus fermented feed could significantly reduce the Vibrio density in the water body on day 21(P<0.05). Also the concentration of serum total protein in each experimental group was significantly higher than that of the control group (P<0.05). The activities of serum peroxidase, superoxide dismutase and phenol oxidase in group of L. acidophilus fermented feed increased significantly compared with the other experimental and control groups (P<0.05), the activities of serum peroxidase and phenoloxidase in serum of shrimp fed by S. cerevisiae fermented feed were significantly high than that in the control (P<0.05). Complex bacteria fermented feed could significantly increase the activities of serum lysozyme, peroxidase and phenoloxidase (P<0.05). However, the activity of detected immune-related enzymes in group of B. subtilis was not increased significantly compare with the control group (P >0.05), except the total serum protein, which was higher than the control. The results also showed that the concentration of ammonia nitrogen and nitrite nitrogen in the water column of each experimental group at the end of the experiment were significantly lower comparing with the control., and the best effect in reducing the concentration of ammonia nitrogen in the water body was found in the group of S. cerevisiae, while the best effect in reducing the concentration of nitrite nitrogen was found in group of L. acidophilus. In summary, it can be seen that shrimp feed fermented by B. subtilis, S. cerevisiae and L. acidophilus singly or in combination could improve the survival rate, growth performance and immunity of shrimp in a degree, and reduce the concentration of ammonia nitrogen and nitrite nitrogen in aquaculture water, but L. acidophilus show great potential as the candidate probiotic used for shrimp feed fermentation. In short, the results in this investigation will provide a theoretical basis for developing of shrimp fermentation feed, which can improve feed utilization rate and survival rate in shrimp aquaculture. |
