Does supplementation with effective microorganisms under recirculating aquaculture system conditions affect water and intestinal microbiome of common carp?

The efficacy of effective microorganism products in aquaculture covers multiple aspects that act directly on fish, such as improving resistance to fungal, bacterial, and viral infections, reproduction, feed efficiency, and overall growth performance, or indirectly through improved water quality. In this study, the application of two commercial water and two commercial food Effective Microorganism supplements was tested under recirculating aquaculture system conditions for their effect on the water and intestinal microbiome of common carp (Cyprinus carpio), as well as on carp growth performance. Neither the dynamics of alpha diversity nor the abundance of single genera followed a pattern related to the experimental setup defined by the supplementation. However, the effects of supplementation were clearly manifested by an increase in the final weight of the fish. The most consistent alteration was a significant increase in Lactococcus abundance in the intestinal microbiome compared to that in the control group, as observed in both experimental setups. We conclude that feed supplementation with Lactococcus enhances its intestinal abundance in fish and promotes improved growth performance, likely through mechanisms involving glucose absorption and metabolism, as demonstrated in previous studies.