A review of ammonia toxicity on aquatic organisms: Species-specific responses, microbial shifts, and environmental interactions

Ammonia (NH₃) is a widespread environmental pollutant with significant ecological and physiological impacts on aquatic organisms. While ammonia plays a key role in nitrogen cycling, excessive amounts disrupt homeostasis and cause toxic effects in various species. Its toxicity is influenced by environmental conditions such as pH, temperature, and salinity, with un-ionized ammonia being especially harmful due to its high membrane permeability. High ammonia levels impair ion balance, disturb nitrogen metabolism, trigger oxidative stress, affect neurophysiological functions at the intracellular level. Furthermore, ammonia can damage vital tissues, eliciting species-specific differential responses (fish, invertebrates, and amphibians), and impair survival, development, reproductive ability, and even movement. In addition, ammonia can alter the microorganisms' composition and metabolic functions. These findings highlight a complex relationship between microbial changes and host health conditions. Therefore, this review can aid in understanding the profound toxicity of ammonia, which affects both organisms and microorganisms, while emphasizing the need for monitoring and management strategies. As climate change intensifies environmental variability, a more profound understanding of ammonia toxicity is essential for protecting aquatic biodiversity and maintaining ecosystem stability.