Bacterial Community Dynamics and Ecological Characteristics in Temporary Holding Water of Live Seafood Tanks

Temporary holding water in live aquatic-product markets represents a short-term, animal-associated aquatic microenvironment, but its bacterial community dynamics remain poorly understood. In this study, 16S rRNA gene amplicon sequencing was used to characterize bacterial communities in holding water of Anguilla japonica, Sinonovacula constricta, and Ruditapes philippinarum. Samples were collected in the morning and evening to evaluate taxon-associated differences and short-term temporal shifts. The bacterial communities showed clear differentiation among the six animal–time groups. Anguilla japonica holding water showed distinct bacterial assemblages from the two bivalve-associated systems, whereas S. constricta and R. philippinarum holding water exhibited more pronounced morning-to-evening changes. In particular, R. philippinarum holding water had higher bacterial richness and a larger proportion of group-specific taxa in the morning, suggesting greater initial community heterogeneity. In addition, the occurrence–abundance analysis showed that taxa with broader distributions tended to have higher mean relative abundances, whereas Rud_8 contained a comparatively large proportion of low-occurrence taxa. Overall, this study demonstrates that live aquatic-product holding water harbors taxon-specific and time-responsive bacterial communities. These findings provide preliminary ecological insight into microbial dynamics in market-associated artificial aquatic microenvironments and highlight the need to consider aquatic animal type and sampling time in future water-quality monitoring.