Advances in response mechanisms of fish to ammonia stress: A review

Ammonia stress has emerged as a critical challenge in global aquaculture, driving extensive research into fish response mechanisms spanning physiological, molecular, and ecological dimensions. This review synthesizes advances in understanding multi-tiered adaptations, including branchial ammonia excretion, urea/glutamine conversion pathways, and microbial symbiosis-mediated detoxification. Key findings highlight species-specific strategies: teleosts prioritize oxidative stress mitigation via Nrf2/glutathione redox regulation, while ureogenic species enhance urea cycle enzyme activities. Microbial communities in aquatic ecosystems further modulate ammonia dynamics through nitrification and denitrification processes. Current mitigation approaches ranging from bioaugmentation and photocatalytic oxidation to dietary antioxidants like probiotics and polyphenols demonstrate efficacy but face limitations in scalability and ecological compatibility. Emerging technologies such as CRISPR-edited ammonia-tolerant strains, real-time water quality monitoring, and circular bioeconomy models (e.g., algal bioconversion of effluents) may represent paradigm-shifting solutions. Future research must integrate multi-omics platforms with ecological modeling to decode evolutionary trade-offs between detoxification energetics and growth performance, ultimately enabling precision aquaculture systems that harmonize productivity with environmental resilience. This comprehensive analysis not only refines theoretical frameworks for ammonia toxicity but also contributes to developing effective strategies for sustainable aquaculture management and addressing the ongoing challenge of ammonia pollution.