Aquaculture affects wild fish populations through feed use, disease transmission, and pollution. These ecosystem impacts have welfare implications for wild animals beyond the farmed species.
Aquaculture ecosystem impacts extend the welfare calculus far beyond the farmed animals to the wild fish and marine animals affected by production. The billions of small pelagic fish harvested for fishmeal represent a massive welfare and conservation concern — these are sentient fish caught and killed in large numbers to produce feed for higher-trophic farmed species. Sea lice transmitted from salmon farms to wild salmon populations cause welfare harm to wild fish that have no benefit from the system driving their exposure. Escaped farmed salmon compromise wild population fitness through hybridization. These ecosystem welfare impacts argue for different aquaculture models: plant-based feeds, shellfish and algae production that improves water quality, and recirculating systems that eliminate escape and disease transmission. The welfare accounting for aquaculture must include all affected species, not just those in the pens.