Each year, more than two trillion fish are killed to feed the world — a staggering figure that barely registers in public awareness.
But now, a groundbreaking study published in Scientific Reports is pulling those deaths out of obscurity, showing that fish not only suffer — they often endure long, intense pain during slaughter. And thanks to a new scientific tool, that pain can now be measured in minutes.
Until now, animal suffering has had no standard unit, unlike CO₂ emissions or public health metrics. Enter the Welfare Footprint Framework (WFF) — a tool that translates suffering into time-based units, from mild discomfort to disabling pain. In this latest study, scientists used WFF to examine the slaughter of rainbow trout, a widely farmed species.
Their findings were shocking: trout can suffer for up to 25 minutes when killed by air asphyxiation, one of the most common global slaughter methods. During this time, the fish experience gill collapse, gasping, muscle exhaustion, and neurological distress. Pain levels vary, but many endure 10+ minutes of pain categorized as hurtful, disabling, or outright excruciating.
What can be done? The study highlights electrical and percussive stunning as effective interventions. Properly applied, electrical stunning could save 60 to 1,200 minutes of suffering per dollar spent — one of the most cost-effective welfare upgrades in animal agriculture. However, inconsistent equipment, training, and oversight have limited its impact.
Percussive stunning — a targeted blow to the fish’s head — is highly effective in controlled conditions but difficult to scale due to size variation and worker fatigue.
Though sometimes seen as a gentler option, ice slurry and chilling methods actually prolong pain for cold-adapted species like trout. Far from humane, ice exposure delays unconsciousness and can cause thermal shock and tissue damage, compounding fear and suffering.
While the study focused on trout, researchers stress that similar pain mechanisms — oxygen loss, blood pH imbalance, metabolic collapse — occur in salmon, catfish, tilapia, seabass, and other farmed fish.
The WFF can be adapted across species, provided there’s detailed physiological data to guide its use.
