A Stage-Aligned Disease Management Framework for Aeromonas hydrophila in Aquaculture: Implications for Antimicrobial...

Aeromonas hydrophila remains a persistent challenge in freshwater aquaculture despite extensive research and the availability of multiple disease-control strategies. Although antibiotics are widely used, alternative approaches including probiotics, immunostimulants, vaccines and bacteriophages are often evaluated in isolation. Increasing evidence indicates that disease outbreaks are not driven by pathogen presence alone, but by dynamic interactions among host condition, environmental stability and pathogen virulence. This review synthesises evidence from 45 controlled intervention studies to propose a stage-aligned framework for managing A. hydrophila, in which disease progression reflects increasing system instability. Stage I (Baseline Prevention) focuses on biosecurity, water quality management and microbiome stability. Stage II (Immune Priming) addresses early risk conditions characterised by elevated stress and immune responses alongside increasing pathogen load, where immune modulation, functional feeds and prophylactic vaccination enhance host resilience. Stage III (Containment) involves targeted interventions, including bacteriophage application, environmental correction and strengthened biosecurity to limit pathogen amplification and transmission. Stage IV (Emergency Control) represents acute outbreak conditions requiring integrated responses, including disinfectant application, emergency biosecurity measures and diagnosis-guided antibiotic use where legally permitted. Reported relative percent survival (RPS) varies substantially between laboratory and field conditions, highlighting the context-dependent performance of interventions. By prioritising intervention timing and system condition over intrinsic tool efficacy, this framework supports reduced antimicrobial reliance while maintaining production stability in intensive aquaculture systems.