Water quality parameters including oxygen, ammonia, temperature, and pH are the primary determinants of welfare for fish in aquaculture systems.
Water quality is to fish welfare what air quality is to terrestrial animal welfare — a fundamental environmental parameter that, when inadequate, causes continuous physiological stress and suffering. Fish in water with low oxygen, elevated ammonia, or inappropriate temperature cannot escape these conditions and experience chronic respiratory distress, tissue damage, and immune compromise as a consequence. The welfare implications of poor water quality are immediate and measurable through behavioural indicators such as surface breathing and reduced feeding, and longer-term through growth depression, disease incidence, and mortality. Modern aquaculture technology makes excellent water quality management achievable, but economic pressures and management failures mean that water quality welfare problems remain widespread in less regulated systems.