Positive and negative effects of recirculating aquaculture water advanced oxidation: O3 and O3/UV treatments improved water quality but increased antibiotic resistance genes

Recirculating aquaculture systems (RASs) can be efficiently used for aquaculture, and oxidation treatment is commonly used to improve water quality. However, the effects of oxidation treatments on aquaculture water safety and fish yield in RASs are poorly understood. In this study, we tested the effects of O3 and O3/UV treatments on aquaculture water quality and safety during culture of crucian carp. O3 and O3/UV treatments reduced the dissolved organic carbon (DOC) concentration by ∼40% and destroyed the refractory organic lignin-like features. There was enrichment of ammonia oxidizing (Nitrospira, Nitrosomonas, and Nitrosospira) and denitrifying (Pelomonas, Methyloversatilis, and Sphingomonas) bacteria, and N-cycling functional genes were enriched by 23% and 48%, respectively, after O3 and O3/UV treatments. Treatment with O3 and O3/UV reduced NH4+-N and NO2--N in RASs. O3/UV treatment increased fish length and weight as well as probiotics in fish intestine. However, high saturated intermediates and tannin-like features induced antibiotic resistance genes (ARGs) in O3 and O3/UV treatments, by 52% and ∼28%, respectively, and also enhanced horizontal transfer of ARGs. Overall, the application of O3/UV achieved better effects. However, understanding the potential biological risks posed by ARGs in RASs and determining the most efficient water treatment strategies to mitigate these risks should be goals of future work.