Crowding is the primary welfare challenge in salmon aquaculture. High stocking densities cause chronic stress, suppress immunity, and dramatically increase disease vulnerability.
Crowding in salmon aquaculture creates a cascade of welfare harms. The chronic stress of living at high density suppresses immunity, making salmon more vulnerable to the diseases that then require treatment — often with medications that themselves affect welfare. The crowding-disease-treatment cycle is one of the defining welfare problems of industrial salmon farming. Individual fish welfare within crowded pens is highly variable: dominant fish access food; subordinate fish may be chronically nutritionally deprived. Fin damage from aggression at high densities is a welfare indicator that is directly observable and used in certification schemes. Reducing stocking density is the most direct structural intervention for improving salmon welfare — it addresses the root cause rather than managing downstream consequences.