Atlantic Salmon Aquaculture: Comprehensive Welfare Review

Atlantic Salmon Aquaculture: The Global Welfare Challenge

Atlantic salmon (Salmo salar) is one of the world's most valuable farmed fish, with global aquaculture production exceeding 2.5 million tonnes annually — predominantly from Norway, Chile, Scotland, and Canada. As a sentient species capable of experiencing pain and suffering, and farmed in vast numbers, salmon aquaculture welfare represents one of the most significant animal welfare challenges in agriculture.

Sea Lice: The Greatest Welfare Challenge

Salmon lice (Lepeophtheirus salmonis and Caligus spp.) are ectoparasites that attach to salmon skin, mucus, and scales. At low infestations, lice cause localised skin damage. At high levels, they cause extensive lesions, secondary bacterial infections, stress, and mortality. Sea lice are the primary disease and welfare challenge in open-net sea cage salmon farming worldwide.

Control methods include: medicinal treatments (bath treatments with hydrogen peroxide, azamethiphos; in-feed medications like EMB), biological control (using cleaner fish — wrasse and lumpfish that eat lice from salmon skin), and physical/mechanical treatments (laser systems, fresh water treatments, warm water treatments). All treatments themselves cause some welfare compromise; balancing louse burden against treatment stress is a key welfare management challenge.

Cleaner Fish Welfare

Wrasse (various species) and lumpfish are used as biological lice control in salmon cages. These cleaner fish themselves have welfare needs that have historically been neglected. They are often produced at very high densities, given inadequate feed when lice are scarce, and suffer high mortality rates. Growing recognition of cleaner fish welfare has led to improved production standards and welfare guidelines.

Crowding and Stocking Density

Norwegian regulations specify maximum stocking densities of 25 kg/m³ in sea cages. Research shows welfare indicators improve at densities below 15-20 kg/m³. Crowding for treatments, harvesting, and inspection causes acute stress and injury.

Infectious Disease

Pancreas disease (PD), cardiomyopathy syndrome (CMS), amoebic gill disease (AGD), and bacterial infections including furunculosis and winter ulcers cause significant welfare compromise. Vaccination has transformed bacterial disease management; viral diseases remain challenging despite ongoing vaccine development.

Slaughter Welfare

Commercial salmon slaughter has undergone significant welfare improvement. Percussive stunning, electrical stunning, and CO₂ stunning before killing are replacing live-bled and live-chilled approaches. EFSA slaughter guidelines recommend effective stunning before any painful killing method. Scotland's Code of Practice mandates humane slaughter. Pre-slaughter stress (crowding, fasting, pump transfer) affects fish welfare and product quality simultaneously — providing alignment between welfare and commercial interests.

Genetic Selection

Selective breeding programmes select for disease resistance, growth rate, and feed conversion. Welfare-relevant traits including louse resistance, spinal deformity reduction, and cataract resistance are increasingly incorporated into breeding objectives, demonstrating that genetic selection can improve welfare alongside productivity.

This page is part of the Animal Welfare Hub — providing evidence-based information to improve the lives of animals. Return to home.