Effects of live microalgae and algae powder on microbial community, survival, metamorphosis and digestive enzyme activity of Penaeus monodon larvae at different growth stages

Abstract

Most hatcheries use live microalgae and algae powder for artificial rearing; however, the effects of these different diets on the rearing process and bacterial communities is not clear. In order to investigate the effects of live algae and algal powder on the larval culture of Penaeus monodon. Two kinds of live algae (Chaetoceros muelleri, Thalassiosira weissflogii) and Spirulina powder were used to feed larvae in this study, and the effects on the environmental parameters of water, the digestive enzymes activity of larvae and the bacterial community from the zoea stage to the post larval (PL) stage were explored. The results revealed that feeding larvae with C. muelleri significantly improved the enzymatic activity of amylase and the survival rate of the larvae, and significantly reduce the concentrations of NH4-N, NO2-N and the quantity of Vibrio in the water (P < 0.05). Feeding with T. weissflogii significantly improved the enzymatic activity of lipase and pepsin, and the percentage of metamorphosis (P < 0.05). It suggested that adding live microalgae was beneficial in increasing the diversity of the bacterial community in larvae. Cyanobacteria and Patescibacteria were dominant bacteria in the algal solutions of C. muelleri and T. weissflogii. The entire rearing environment was dominated by two phyla: Bacteroidetes and Proteobacteria. Virgulinella fragilis, the bacteria present in the liquid of C. muelleri and T. weissflogii, accounts for a high proportion of bacteria in the rearing water at the zoea stage. The bacterial community in the zoea stage showed significant negative correlations with NH4-N and NO2-N (P < .05), whereas the bacterial community in the PL stage showed significant positive correlations with NH4-N and NO2-N (P < .05). Saprospiraceae and Microbacteriaceae in the water were significantly positively correlated with NH4-N and NO2-N (P < .05). Feeding larvae with C. muelleri and T. weissflogii and Spirulina powder could increased the abundance of Microbacteriaceae, Devosiaceae and Saprospiraceae at the family level, and increased the abundance of Pseudoalteromonas, Roseovarius and Nautella at genus level. In conclusion, feeding larvae with live microalgae could improve the percentage of metamorphosis and survival rates of larvae by improving the external water environment, enhancing digestion, and regulating bacterial community.