Comparison of the Effects of Shrimp Feed Fermented by Bacillus subtilis, Saccharomyces cerevisiae, and Lactobacillus acidophilus on the Culture of Penaeus vannamei

Penaeus vannamei is an important shrimp species that is farmed globally, owing to its fast growth and good environmental adaptability. However, vibriosis outbreaks, such as acute hepatopancreatic necrosis disease and translucent post-larva disease, have become a considerable constraint on the development of the shrimp aquaculture industry globally in recent years. Due to the negative consequences associated with the use of antibiotics to control bacterial diseases, alternative technologies, such as improving shrimp immunity, the nutrition level of shrimp diets, and the ecological environment of shrimp ponds by using probiotics, have been developed. Owing to the limitations related to the sourcing and cost of fish meal, a large amount of vegetable protein is often used as a fish meal substitute in shrimp artificial feed, which is not only difficult for the shrimp to digest and absorb but can also lead to nutritional antagonism. In order to improve the health status of aquaculture animals by providing high-quality feed, the development and optimization of fermented feed have received extensive attention. Probiotics 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 growth performance, and enhance the immunity of shrimp.In this study, in order to explore the application effects of shrimp feed fermented by different probiotic bacteria, probiotic strains, including Bacillus subtilis, Saccharomyces cerevisiae, and Lactobacillus acidophilus, were used individually and in combination for the fermentation of commercial feed and fed to shrimp (P. vannamei) for 28 days. The survival, body length growth, specific growth, and feed conversion rates 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. Furthermore, ammonia nitrogen and nitrite nitrogen concentrations in the water column were compared between the groups.The results demonstrated that the survival rates of shrimp in the 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 the B. subtilis and L. acidophilus groups were significantly higher than that of the control group (P < 0.05), while the feed conversion rate in the L. acidophilus group was significantly decreased compared with that of the control group (P < 0.05). There was no significant difference in the specific growth rate of shrimp between the experimental groups and the control group (P > 0.05). Fermented feed can affect the composition of bacteria in the 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 the short term (within 14 days) had no significant effect on reducing the total density of Vibrio in the water. However, feeding B. subtilis and L. acidophilus fermented feed significantly reduced the Vibrio density in the water body on day 21 (P < 0.05). In addition, the serum total protein concentration in each experimental group was significantly higher than that in the control group (P < 0.05). The activities of serum peroxidase, superoxide dismutase, and phenoloxidase in the L. acidophilus fermented feed group increased significantly compared with those of the other experimental and control groups (P < 0.05). The activities of serum peroxidase and phenoloxidase in the serum of shrimp fed S. cerevisiae fermented feed were significantly higher than those of the control group (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 the detected immune-related enzymes in the B. subtilis group did not increase significantly compared with that of the control group (P > 0.05), except for the activity of total serum protein, which was higher than that of the control group. The results also revealed that the concentration of ammonia nitrogen and nitrite nitrogen in the water group of each experimental group at the end of the experiment was significantly lower compared to that of the control group. S. cerevisiae and L. acidophilus groups had the best effect in reducing the concentration of ammonia nitrogen and nitrite nitrogen in the water, respectively.In summary, 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 to a degree, and reduce the concentration of ammonia nitrogen and nitrite nitrogen in aquaculture water. Moreover, L. acidophilus shows great potential as a candidate probiotic for shrimp feed fermentation. The results of this study provide a theoretical basis for the development of shrimp fermentation feed, which can improve the feed utilization and survival rates of shrimp in aquaculture.