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An illustration of Lynne Sneddon. Rebecca Clarke for Vox

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We didn’t know fish feel pain. Then the zoologist Lynne Sneddon came along.

Over the last decade our understanding of how fish experience pain has greatly advanced, thanks in large part to Sneddon’s pioneering work.

Kenny Torrella is a staff writer for Vox’s Future Perfect section, with a focus on animal welfare and the future of meat.

By one estimate, we catch or farm 840 billion to 2.5 trillion fish each year. That’s at least 10 times as many chickens, pigs, and cows farmed for food.

But the animal welfare movement — along with food companies and policymakers — has largely ignored the welfare of fish. That’s because it’s not until recently that science has caught up on the question of how fish experience pain.

Much of that science can be chalked up to the work of Lynne Sneddon and her colleagues.

Sneddon, a zoologist, set up a research program in 1999 at the Roslin Institute in Edinburgh, Scotland to investigate fish pain with her colleagues Michael J. Gentle and Victoria Braithwaite. (Braithwaite went on to publish the seminal book on fish pain, aptly titled Do Fish Feel Pain?, in 2010, and died in 2019.)

A couple years later, Sneddon set up a research laboratory to study fish pain at the University of Liverpool; she now teaches and conducts research at the University of Gothenburg. Sneddon and her colleagues’ early research inspired others to investigate fish pain and welfare, which eventually developed into a robust academic field. Their findings have also seeped into mainstream media, slowly changing the perception of fish from robotic creatures merely reacting to noxious stimuli to sentient beings who can feel pain.

Over her more than 25-year career, Sneddon has conducted a number of studies investigating the capacity fish have for pain. In 2002, she was the first to discover the existence of nociceptors in fish — sensory neurons that identify and react to harmful stimuli, an important biological marker for fish pain capacity, and the leading theory on what causes them to experience it.

Here’s an excerpt from an article I wrote about fish pain last year, detailing one of the many experiments she’s conducted:

In one of their experiments with rainbow trout, the researchers dropped Lego blocks into a tank to see how the fish would react. Normally, trout would avoid novel objects like Lego blocks out of fear. But when injected with a shot of acetic acid, the trout were less likely to avoid the Legos, as they were focused more on their own pain than avoiding a potential threat. When injected with both the acid and morphine, the trout avoided the blocks as they typically would.

Sneddon’s work is paying off. There’s now a small but growing movement to reduce the suffering of the trillion or so fish we eat each year, both on fish farms and during slaughter. And earlier this year, the UK passed a law declaring fish and decapods, like crabs and shrimp, as sentient. It’s hard to imagine such a law passing just a decade ago.