Aquaculture effluent — containing excess feed, feces, and chemicals — affects the welfare of farmed fish and wild aquatic animals in surrounding water bodies.
Aquaculture effluent creates a welfare commons problem: farmed fish benefit from high-density rearing while wild fish in surrounding waters pay welfare costs through effluent impacts. Oxygen depletion causes stress and asphyxia in wild fish; sea lice spreading from farm to wild populations cause the same welfare harm as in farmed fish. Contained RAS systems solve the effluent problem but are more expensive — creating regulatory pressure as the key driver for industry adoption.