Do fish feel pain? Why some scientists are split on the debate

Fish often avoid intense stimuli, but scientists and animal welfare groups have long debated whether fish can feel pain. So is there an answer?

Animal rights organization PETA claims on its website that fish do feel pain and advocated for people not to catch, farm or eat them. Meanwhile, other scientists ‒ including Ana Zangroniz, a Florida sea grant extension agent at the University of Florida ‒ contested PETA's conclusion and said people who believe fish are in pain are actually seeing fish's response to stress.

"Some of what the 'pro' field, if you will, have captured is they're showing fear to certain stimuli," said Zangroniz. "They're showing changes in ventilation rate. They're showing stress in terms of change in behavior."

So, do the aquatic creatures (and sometimes beloved pets) actually feel pain?

Do fish feel pain?

That's still a debate among scientists. Zangroniz said too much is unknown about fish to say they can or cannot feel pain. The tough part is that fish cannot be compared to other species, she said, like mammals or birds.

"That has a lot to do with their anatomy and physiology and the way that their brains and their pain receptors are structured," she said.

Sharks and rays do not possess nociceptors, which Zangroniz said is key for transmitting the feeling of pain to the brain.

Studies like the one PETA referenced, conducted by biologist Victoria Braithwaite, showed fish's behavior changed when given painful stimuli and they expressed avoidance if a tissue was injured. Other studies have said fish don't feel pain as they lack the neural tissue required for sensing pain. Studies have instead found evidence of people projecting feelings of pain onto the animals' reactions.

University of Leicester Fish Biology and Fisheries Professor Paul Hart agreed with Zangroniz and added that for the European Union and the United Kingdom, asserting that fish can feel pain comes with legal regulations that must be enforced. He said an animal must be self-aware to feel pain.

"Unless you're aware of yourself as a conscious being, you don't suffer from pain in the same way as if you were just reacting instinctively to an unpleasant stimulus and taking evasive action," he said.

What level of pain do fish feel?

That, too, is unknown. Zangroniz said studies only use a few species of fish and don't represent the more than 30,000 fish species that exist. She added pain is measured in mammals on the grimace scale, often seen in doctor's offices with a happy to sad face.

"They're for mammals, not just humans, but dogs, cats and raccoons − they're looking for changes in facial expression, and so that's an example of a pain test that really wouldn't be applicable in trying to measure that sort of change in fish, because they can't change facial expressions," she said.

How can I tell if a fish is in pain?

Despite us not really knowing if fish can feel pain, both Hart and Zangroniz said fish do visibly respond to stress or unpleasant stimuli by swimming away from the origin.

Still, Zangroniz said if a person has pet fish and notices they're floating in the tank or swimming erratically, they can try to remove variables that draw out stress from the fish or seek medical help from a fish health specialist.

One thing that is not recommended: releasing fish into a local aquatic wildlife setting. Many pet fish are exotic to the U.S., she said, and doing so could release an invasive species or unknown bacteria in the local aquatic system.

"Depending on where you live, I would consult your local fish and wildlife department," Zangroniz said.

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Contact reporter Krystal Nurse at knurse@USATODAY.com. Follow her on X, formerly Twitter,@KrystalRNurse, and on BlueSky @krystalrnuse.bsky.social.