Scientists prove fish suffer "intense pain" for at least 10 minutes after catch, calls made for reforms

Each year, more than two trillion wild and farmed fish are killed to feed humanity. Their deaths often go unnoticed. Yet beneath the surface is a simple biological fact: fish can suffer.

Rainbow trout, a species farmed and consumed across the globe, experience not just death – but a prolonged and intense form of distress when killed by air asphyxiation.

A new study published in the journal Scientific Reports shines a light on this pain and offers a pathway to reduce it.

Fish pain needs better measurement

Unlike environmental impact or public health, animal suffering lacks a universal metric. There are no equivalents to carbon footprints or life years lost. To address this, scientists developed the Welfare Footprint Framework (WFF).

This tool measures pain in minutes, allowing researchers to compare welfare outcomes across species and conditions. The research team applied this method to trout slaughter, where air exposure is still a widely used technique.

Fish, when pulled from water, begin a slow and stressful decline. Their gills collapse. They gasp in panic. Their blood chemistry spirals. Oxygen disappears while carbon dioxide builds.

These biological reactions unfold as the fish continues to move, gasp, and suffer – sometimes for as long as 25 minutes.

Fish suffer up to 25 minutes

The researchers divided the trout’s suffering into four time segments. These range from alarm at removal to the final depression of brain activity before unconsciousness.

Through behavioral, neurological, and pharmacological evidence, the team estimated that the average trout endures about ten minutes of pain that qualifies as hurtful, disabling, or excruciating.

In some conditions, this could stretch beyond 20 minutes. When adjusted by weight, that translates to 24 minutes of such pain per kilogram (about 11 minutes per pound) of fish killed.

The team used neurophysiological data like EEG signals and reflex loss to identify unconsciousness. They reviewed how fish respond to CO₂, pH imbalance, muscle exhaustion, and fear-inducing stimuli. Each pain level had specific criteria, ranging from annoyance to total disruption of basic functions.

Current methods cause painful deaths

Air asphyxiation is still legal and common in many parts of the world. But it is neither quick nor painless. Chilling in ice or using ice slurry might sound gentler, yet for cold-adapted species like trout, this method just slows down metabolism.

This can delay loss of consciousness even further, compounding the suffering. Ice exposure also risks tissue damage, thermal shock, and prolonged fear.

The research shows that suffering does not always begin at the point of slaughter. It often starts well before.

Crowding, transport, and handling all add to the fish’s cumulative pain. These pre-slaughter stressors can cause physical injury and hours of distress. Yet, regulations usually overlook them.

Stunning can help fish suffer less

The study evaluated two types of stunning: electrical and percussive. Electrical stunning, if properly used, could spare 60 to 1,200 minutes of suffering for every dollar spent. This makes it one of the most cost-effective welfare interventions known.

But implementation remains inconsistent. In many commercial settings, electrical stunning fails to reliably render fish unconscious. Poor placement of electrodes, inadequate voltage, or faulty machines may undermine the potential benefits.

Percussive stunning – a physical blow to the head – has shown better consistency in lab settings. But it’s difficult to scale. Fish vary in size. Equipment must be precisely calibrated. Worker fatigue also reduces effectiveness. Any slip means the fish remains conscious while bleeding out.

A new language for animal pain

What makes the Welfare Footprint Framework powerful is its transparency. Instead of assigning a fixed label to pain, it works with probabilities. If scientists believe there’s a 40% chance the pain is disabling and a 40% chance it is excruciating, the framework includes both.

This makes the model flexible and more reflective of real-world uncertainty. Pain, like emotion, varies between individuals. Some fish may suffer more than others, even under identical conditions.

“The Welfare Footprint Framework provides a rigorous and transparent evidence-based approach to measuring animal welfare, and enables informed decisions about where to allocate resources for the greatest impact,” noted Dr. Wladimir Alonso from Welfare Footprint Institute.

This approach mirrors models used in public health or environmental science. Just like life years lost to disease, we can now talk about minutes of suffering saved.

Implications for policies and people

Fish slaughter occupies only minutes in an animal’s life – but these minutes can be extremely painful. Compared to long-term reforms on farms, slaughter improvements are easier to implement and affect billions of lives.

The study’s authors argue that investing in better stunning tools and training workers can provide enormous welfare gains.

For policy makers, this research offers a scientific foundation to reform outdated practices. Certification schemes can set minimum stunning effectiveness based on real pain data.

Governments can use this to guide humane slaughter laws. For consumers, it gives a new way to think about what ends up on their plate.

Other fish suffer too

Though this study focused on rainbow trout, the underlying stress pathways – oxygen deprivation, acidosis, metabolic failure – are common across fish species. That means the Welfare Footprint Framework can be adapted.

Salmon, catfish, seabass, tilapia – they all may suffer in similar ways during air exposure. However, each species will need specific data.

Some tolerate low oxygen better. Others may react more strongly to ice. Future research must expand to include this diversity.

A turning point for aquatic welfare

The world is just beginning to reckon with the sentience of fish. For decades, their pain was denied or ignored. But science no longer allows that.

With trillions of fish slaughtered every year, even small improvements can have vast impact.

The WFF doesn’t just measure pain. It opens a language of empathy grounded in evidence. It lets regulators, producers, and consumers weigh the cost of change.

And perhaps, most importantly, the framework acknowledges what fish have felt all along – suffering that deserves to be seen and reduced.

The study is published in the journal Scientific Reports.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–