Hydrogen peroxide (H₂O₂) is a disinfectant for recirculating aquaculture systems (RAS), yet its impacts on microbial communities remain insufficiently characterized. In this study, we evaluated the effects of repeated H₂O₂ additions (5, 15, and 30 mg/L) on microbial community composition in both biofilter biofilms and rearing water of marine RAS culturing juvenile Hexagrammos otakii . Using 16S rRNA gene amplicon sequencing, we found that higher H₂O₂ concentrations led to a significant decline in alpha diversity, with Shannon index in biofilm decreasing from 4.84 ± 0.39–4.47 ± 0.52 at 30 mg/L, and water microbial richness (Chao1) showing a similar downward trend. Community structure analyses (PCoA and Bray-Curtis similarity) revealed that rearing water microbes were more susceptible to H₂O₂-induced disturbances than those in the biofilm, which showed greater structural resilience. Taxonomic shifts highlighted the suppression of key nitrite-oxidizing bacteria (NOB), particularly Candidatus Nitrotoga , under medium and high H₂O₂ treatments, while ammonia-oxidizing bacteria (AOB) remained relatively unaffected. In addition, the relative abundance of potential pathogenic Vibrionaceae decreased from > 15 % to undetectable levels by Day 27 under high H₂O₂ conditions, indicating its potential for pathogen control. These results demonstrate the need to balance H₂O₂ application for disinfection while maintaining microbiome integrity and biofilter function in RAS operations. • Hydrogen peroxide (H₂O₂) altered microbial communities in marine lab-scale RAS. • Biofilms showed greater resilience than rearing water to oxidative disturbance. • Nitrite-oxidizing bacteria are more sensitive to H₂O₂ than ammonia-oxidizing bacteria • Potential vibrionaceae abundance decreased under medium(15 mg/l) and high H₂O₂ (30 mg/l) treatments.
Huang et al. (Fri,) studied this question.