Global Atlantic salmon production exceeds 2.8 million tonnes annually, with Norway, Chile, UK, and Canada as leading producers. Each salmon spends 2-3 years in sea cages after being raised from egg in freshwater hatcheries. The welfare of individual salmon affects both animal welfare outcomes and production quality.
Sea lice remain the primary welfare challenge in salmon aquaculture. Lepeophtheirus salmonis and Caligus spp. cause skin lesions, osmotic stress, and secondary infections. Treatment efficacy and resistance management are central to welfare management. Biological control (cleaner fish), mechanical treatment, and medicinal baths form an integrated management approach.
Atlantic salmon in sea cages are typically stocked at 15-30 kg/m³. High density is associated with increased aggression, fin damage, impaired immune function, and stress-related disease. Welfare research supports maximum densities of 20-25 kg/m³ for good welfare outcomes. Norwegian regulations set 25 kg/m³ as the legal maximum.
The transition from freshwater to seawater (smoltification) is a critical welfare period. Premature transfer to sea before full smoltification causes osmoregulatory stress and compromised immune function. Monitoring smolt readiness through gill sodium/potassium ATPase activity and chloride cell development guides transfer timing.
Percussive stunning followed by gill cutting is the most welfare-positive slaughter method. Electrical stunning in water (ESW) provides effective unconsciousness but requires precise current delivery. CO2 narcosis causes distress before unconsciousness. The Norwegian Mattilsynet has set welfare standards specifying effective stunning before killing — a global benchmark.
The Salmon Welfare Index Model (SWIM) provides validated welfare outcome measures: external injuries (fin condition, scale loss, wounds), behavioral indicators (surface swimming, abnormal schooling), and health parameters (gill health, lice counts, mortality rates). Regular welfare monitoring is integrated into Norwegian aquaculture licensing requirements.