Microbial community structure and function in aquatic environments during the overwintering cultivation of juvenile <i>Apostichopus japonicus</i>

To characterize microbial community structure and function in aquatic environments during the overwintering cultivation of juvenile Apostichopus japonicus , we analyzed water samples from a representative industrial indoor aquaculture facility in Tangshan, Hebei Province. We assessed water quality by measuring key physicochemical parameters and employed 16S rRNA gene sequencing to profile microbial composition and functional traits. Our results revealed that ammonium nitrogen (NH₄-N) levels in surface water during the late pond-transfer stage in Workshop 2# reached 1.494 mg·L⁻¹, significantly exceeding those observed in other samples (P&lt;0.05). Microbial richness in Workshop 1# peaked during the early pond-transfer phase, significantly increasing relative to other timepoints within the same workshop (P&lt;0.05). At the phylum level, Proteobacteria and Bacteroidetes dominated across all samples. Firmicutes represented the third most abundant phylum during early pond-transfer stages, while Actinobacteria ranked third in routine aquatic water. Sulfitobacter and _Polaribacter were prevalent at the genus level during the early pond-transfer phase. Of particular concern, Vibrio showed the highest relative abundance in mid-phase pond-transfer water from Workshop 1#, indicating a potential disease risk. These findings elucidate microbial community shifts in A. japonicus aquaculture systems during overwintering, offering both theoretical insights and practical recommendations for optimizing industrial-scale aquaculture management.