Here’s a horror scenario for your day: you’re pulled into a vacuum. No air, no escape. Your body screams for oxygen. You twist, writhe, panic, but there’s nothing. Now imagine this lasts 10-20 minutes. That’s how billions of fish die every year.

Now, you’re probably thinking “Fish don’t feel the same way I do” — and that’s almost certainly correct. But they do feel, and they do feel pain.

Rainbow trout, among the most farmed fish on Earth, are a good example. According to a new study in Scientific Reports, when these fish are killed by air asphyxiation they endure between 1.9 and 21.7 minutes of pain that lasts from moderate to excruciating.

Fish feel pain

For much of human history, we assumed that animals — especially those unlike us — didn’t really feel pain. Philosopher René Descartes infamously argued that animals were mere automatons, reacting without consciousness, and this view stuck around for centuries, justifying everything from factory farming to invasive research.

Pain was seen as a privilege of the human mind, stemming from our supposed superiority. But science has steadily dismantled that idea. Studies have now shown that mammals, birds, fish, and even some invertebrates like octopuses exhibit behavioral and neurological responses consistent with pain and suffering.

Numerous studies have demonstrated that fish not only detect harmful stimuli but also exhibit prolonged behavioral and physiological responses indicative of pain perception. In 2003, a study showed that fish exhibit nervous and physiological responses consistent with pain. This was subsequently confirmed several times.

Further research across several species found that analgesics such as morphine mitigated these behavioral changes, suggesting the involvement of central pain pathways and not mere reflexes. By now, there’s ample evidence that fish feel pain, that they exhibit stress behaviors when injured, and their brains light up in patterns resembling suffering.

But our practices haven’t really changed that much.

In the new study, researchers from institutions across Europe and the U.S. applied the Welfare Footprint Framework (WFF), a method designed to measure suffering in cold, hard minutes. They focused on what happens when trout are removed from water and left to suffocate in air — still the default in many slaughterhouses.

The team broke down the dying process into four stages:

1. Initial air exposure: The fish begins gasping and panicking. Its gills collapse, and stress hormones spike.
2. Suffocation: Carbon dioxide builds up. Blood pH plummets. The fish feels a growing sense of suffocation — akin to breathlessness in humans.
3. Metabolic exhaustion: Muscles spasm. Lactate floods the system. The fish may feel ischemic pain — pain from oxygen-starved tissues.
4. Depressed brain activity: Eventually, neural function shuts down. Consciousness fades. But that can take as long as 25 minutes.

During that time, the fish likely experiences intense negative emotions: panic, confusion, and pain. This isn’t a metaphor, it’s a biochemical reality.

On average, each trout spends 10 minutes in states classified as “hurtful,” “disabling,” or “excruciating” — categories developed to mirror human experiences. When scaled by weight, that’s around 24 minutes of intense pain per kilogram of fish.

Industrialized cruelty

Humans slaughter between 1 and 2 trillion fish every year. Trillion — that’s a thousand billions. Many of those are wild-caught. But among farmed species — like salmon, trout, and seabass — slaughter happens on land, often by the millions in a single day.

That means trillions of minutes — billions of hours — of avoidable pain. You don’t have to be an animal activist to realize the ethical problems in this. Even if you eat fish, the method of slaughter matters. We care about how chickens are killed. We passed laws to stop boiling lobsters alive. Why do fish get such a bad deal?

The reasons are less to do with science and more to do with policy. Fish don’t scream and aren’t cute. We also eat a lot of them, which means any change will be challenging to implement. But that doesn’t mean they aren’t suffering. It just means we’re bad at noticing (or at caring).

Researchers propose an alternative to limit this suffering.

Electrical stunning, if done right, knocks a fish unconscious in under a second. Percussive stunning (essentially a quick blow to the head) works too. These methods drastically reduce suffering. The researchers estimate that investing just one U.S. dollar into effective stunning could avert up to 20 hours of fish pain. However, we kill a lot of fish every year.

Although modern stunning adds just 3% to a farm’s expenses, many producers don’t bother. Regulations are weak or nonexistent and the fish, as usual, don’t get a say. As a result, outdated methods like air asphyxia — or worse, chilling in ice — are still used. And make no mistake: ice is no gentle euthanasia. Cold slows down metabolism, dragging out the process.

This should matter to us

Fish are complex vertebrates with brains and behaviors shaped by hundreds of millions of years of evolution. To assume they don’t feel pain is no longer scientifically defensible. It’s just a convenient way out.

Fish welfare should be part of that conversation. It’s not just about ethics, it’s about science-based policy. If we care about reducing animal suffering at scale, this is one of the biggest challenges for our species. The least is done to spare them pain, and as the researchers highlight, there’s no technological innovation needed. Producers can invest in better equipment, and certifiers can start including fish in their welfare standards. And consumers — yes, that’s us — can vote with our forks.

If you care about animal welfare, ask your supermarket how their fish are killed. Look for certifications that include stunning. Demand better. Because right now, we’re letting trillions of sentient beings die slowly and invisibly.