Effluent from fish farms affects surrounding water quality and wild fish welfare, requiring effective management to prevent pollution-related suffering in wild populations.
Aquaculture effluent affects wild animal welfare in the surrounding environment — an externality that is rarely considered in farm welfare assessments that focus only on the fish being farmed. Nutrient enrichment from uneaten feed and faecal matter depletes oxygen in localised areas, causing distress and mortality in wild fish. Antiparasitic chemicals — particularly emamectin benzoate and synthetic pyrethroids used against sea lice — are highly toxic to crustaceans at environmental concentrations and affect benthic communities near treatment sites. Land-based RAS systems with effective filtration substantially reduce effluent impacts but require rigorous maintenance. Including wild animal welfare impacts in the environmental assessment of aquaculture operations would provide a more complete picture of the welfare costs and benefits of different production systems.