Effect of Effective Microorganism Inoculants on Bacterial Communities Associated with Brachionus plicatilis

Brachionus plicatilis, a type of rotifer, is a vital live feed in marine aquaculture, particularly during the early developmental stages of fish and crustacean larvae. However, under high-density culture conditions, rotifers tend to accumulate and transport substantial quantities of bacteria, fungi, and other microorganisms present in aquatic environments. Sustainable and efficient methods for suppressing pathogenic microorganisms in B. plicatilis cultures while simultaneously improving its safety and quality as a live feed in aquaculture remain underdeveloped. To address this gap, we investigated the effects of aquatic effective microorganisms (EMs) on the population density and microbial community structure of B. plicatilis under extensive culture conditions. We monitored changes in B. plicatilis population density in response to varying concentrations of the EM inoculants. The diversity, composition, and temporal dynamics of the intestinal and surface microbiota at an optimal EM inoculant concentration and analyzed microbial community dynamics through high-throughput sequencing, which allowed for a precise evaluation of the effects on microbial diversity. Results demonstrated that treatment with a 1.0% EM inoculant for 24 h considerably increased B. plicatilis density while effectively reducing the load of harmful pathogenic microorganisms. Additionally, these results suggest that EM inoculation regulates microbial community structure by inhibiting pathogenic microorganisms and promoting the growth of beneficial bacteria without introducing residual environmental contaminants. Overall, this study offers a viable approach for sustaining aquaculture practices, contributing to global food security initiatives by promoting environmentally friendly and safe fish feed production.