Overlooked risk of dissemination and mobility of antibiotic resistance genes in freshwater aquaculture of the Micropterus salmoides in Zhejiang, China

Residual antibiotics in aquaculture ecosystems can exert selective pressures on bacterial communities, driving bacteria to acquire antibiotic resistance genes (ARGs) through gene mutations or horizontal gene transfer (HGT). This study investigated the antibiotic resistance risk in freshwater aquaculture ecosystems of Micropterus salmoides in Zhejiang Province. The results revealed that oxytetracycline, ciprofloxacin and florfenicol were up to 300 ng/L, and the proportion of multidrug-resistant genes varied from 32.20 % to 50.70 % in the surveyed aquaculture water. Additionally, approximately 9.80 % of all annotated ARGs were identified as possessing plasmid-mediated horizontal transfer risks. The ARGs host prediction revealed that Actinobacteria carried the highest abundance of ARGs, up to 159.38 (coverage, ×/Gb). Furthermore, the abundance of Paer_emrE , ksgA , ompR and golS were positively correlated with Chlorophyll a concentration ( p  < 0.05), suggesting that algal blooms might facilitate the evolution and transfer of ARGs. Correlations between ARG abundances and total phosphorus, total nitrogen, pH, electrical conductivity indicated that modulating water quality parameters may serve as a viable strategy to mitigate the eco-environmental risk of ARGs in aquaculture water. This study identified antibiotic resistance characteristics in freshwater aquaculture ecosystems of Micropterus salmoides in Zhejiang Province, establishing a foundation on managing antibiotic resistance risks in such aquaculture environments.