Pain Management in Farmed Fish: Science and Practice

Pain Management in Farmed Fish: An Evidence-Based Approach

The capacity of fish to experience pain has been established through substantial scientific evidence, yet pain management in aquaculture practice lags far behind that in terrestrial livestock farming. This represents a significant and addressable welfare gap — farmed fish undergo procedures and experience conditions that cause pain and distress, and practical analgesic and anaesthetic interventions exist but are underutilised. This page summarises the evidence for fish pain and provides practical guidance on pain management in aquaculture.

The Science of Fish Pain

The evidence for fish pain and nociception includes:

Nociceptors: Fish possess A-delta and C-type nociceptors comparable to those in mammals, distributed throughout the body
Neuroanatomy: Fish have the neural structures required to process noxious stimuli, including ascending spinal pathways and forebrain regions involved in aversive experience
Physiological stress responses: Tissue damage triggers cortisol elevation, heart rate changes, and neurochemical responses consistent with pain processing
Behavioural responses: Noxious stimuli cause avoidance learning, protective behaviours (rubbing, guarding), and motivational trade-offs suggesting experiential rather than merely reflexive responses
Analgesic responsiveness: Fish treated with analgesics (morphine, lidocaine) show reduced nociceptive behavioural responses — the gold standard test for pain

Key scientific reviews (Sneddon 2018; Braithwaite 2010; Birch et al. 2021 LSE report) have concluded that fish are sentient and that their pain experiences should be taken seriously in welfare legislation and practice.

Painful Procedures in Aquaculture

Common aquaculture procedures causing pain that may be inadequately managed include:

Branding, fin clipping, and PIT tagging (research and management)
Surgical implantation of biologgers
Spawning induction (handling and injection)
Manual stripping (egg/milt collection)
Gill biopsy and health monitoring procedures
Delousing procedures (mechanical sea lice removal)
Transport and crowding (physiological stress causing distress)
Slaughter without stunning (common in many aquaculture contexts)

Available Anaesthetic and Analgesic Agents

Anaesthetics (Sedation and Loss of Consciousness)

MS-222 (tricaine methanesulfonate): Most widely licensed and used fish anaesthetic. Buffered with sodium bicarbonate to reduce acidity. Dose varies by species; reversal by placing in fresh water
AQUI-S (isoeugenol): Approved in several countries (not UK); effective and lower stress response than MS-222 in some species
Clove oil (eugenol): Widely used informally; effective sedation; concerns about induction and recovery smoothness
CO₂: Available and rapid but causes significant distress during induction — not welfare-optimal

Analgesics

Lidocaine (local anaesthetic): Effective topically and by injection; short duration. Used for fin clipping, biopsy
Morphine: Demonstrated analgesic effect in research; not licensed for aquaculture use; research tool only
NSAIDs (meloxicam): Emerging evidence for efficacy in some species; dose regimens being established

Humane Slaughter

Slaughter without prior stunning means fish remain conscious and capable of experiencing pain throughout the dying process. Recommended humane slaughter methods:

Electrical stunning: Most practical for large-scale aquaculture; renders fish immediately unconscious when applied correctly. Specific protocols required per species
Percussive stunning (spiking): Effective individual method; requires skill and consistent technique
Ice slurry: Minimum welfare standard for small-scale harvest; induces sedation within 5–10 minutes depending on species and temperature differential
CO₂ stunning: Less welfare-optimal due to aversive induction; avoid where electrical alternatives exist

Best Practice Recommendations

Use licensed anaesthetic (MS-222) for all handling procedures lasting >30 seconds
Apply lidocaine for any procedure involving tissue damage
Implement electrical or percussive stunning as standard slaughter method
Minimise handling frequency and duration — plan procedures to reduce exposure
Conduct transport in appropriately oxygenated, temperature-controlled water
Monitor for post-procedure welfare outcomes (behaviour, feeding response)