People often assume that fish don’t feel pain. That’s odd because, like other animals we believe can feel pain — horses, dogs, cats, rats, humans — fish are vertebrates. They have the same senses we have (vision, hearing, etc.) plus some.
But they live in a very different environment, and most of us don’t encounter fish often unless they’re on the menu. The world of a fish is so removed from the human world that we have little instinct about what they are or are not feeling.
Or, as Carl Safina, ecologist, and author, put it in an article in The Guardian, “When you are a fish, no one can hear you scream.”
But do fish have anything to scream about? If you think fish do feel pain, or if you think they don’t, the answer probably seems pretty obvious to you. But scientists have been debating the issue for years.
Do Fish Have Pain Receptors?
Nociceptors are sensory receptors, often called pain receptors, that react to noxious stimuli, such as, say, a barbed hook piercing the lip.
Scientists have established that fish do have nociceptors. But while not having nociceptors means not being able to feel pain, having them is not enough to ensure the sensation of pain.
Read More: Yes, Fish Can Communicate Acoustically
Do Fish Have Brains?
In the 2010 paper “Can Fish Really Feel Pain?,” a team of scientists argues that to experience the sensation of pain (or any form of consciousness), an animal must have a neocortex. The neocortex is the part of the brain that processes higher functions such as cognition and perception. Fish do not have a neocortex — only mammals do. Thus, according to this reasoning, fish do not feel pain.
This is reassuring to many people who eat fish or catch fish for sport.
But not all scientists are convinced this settles the issue. As Jonathan Balcombe points out in What a Fish Knows: The Inner Lives of Our Underwater Cousins, birds are widely considered to be conscious, but they, too, lack a neocortex. So a neocortex doesn’t seem to be necessary for an animal to be considered conscious and, therefore, capable of experiencing pain.
Though a fish does not have a neocortex, it does have a pallium. Balcombe, ethologist and former director of animal sentience with the Humane Society Institute for Science and Policy writes that the pallium “serves the functions for fishes that the neocortex does for mammals.”
Do Fish Feel Pain When Hooked?
Much of the evidence that fish feel pain is derived not only from neuroanatomy but from behavior as well. Lynne Sneddon, a zoologist who studies fish pain at the University of Gothenburg, and one of the researchers who established that fish have nociceptors, has done some intriguing work on how fish respond to what we might expect would cause pain.
In one study, Sneddon and colleagues injected the mouths of fish with acetic acid (vinegar). The fish showed signs of discomfort, such as rocking from side to side, rubbing their noses against the side of the tank, and a greatly increased rate of gill opening and closing. When the fish were given painkillers, these behaviors decreased.
Those who reject the idea that fish can feel pain say that the rocking and rubbing of Sneddon’s fish and the thrashing of that big bass you just hooked is no more than an instinctive reaction, much like the way your hand jerks away from a hot stove — moments before you register the pain. According to this view, the fish’s reaction doesn’t necessarily mean it is experiencing anything like what we would call pain.
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Do Fish Seek Pain Relief?
Other of Sneddon’s experiments are perhaps more convincing. As described in What a Fish Knows, Sneddon injected zebrafish with acetic acid and gave them the option of two chambers within their tanks. One was what researchers call “enriched.” It was filled with vegetation, things to explore, and places to hide. The other contained just plain water.
Whether they’d been injected or not, the fish preferred the enriched chamber. But when Sneddon dissolved painkillers in the plain chamber, the fish that had been injected with acetic acid left the enriched tank for, presumably, the pain relief offered by the other chamber. This writes Balcombe, suggests that fish are willing to “pay a cost to get pain relief.”
Can Fish Feel Pain?
Though the issue may not be completely settled, animal welfare experts are beginning to accept the idea that fish can likely feel pain. The UK’s animal welfare law now accords sentience to fish, along with all other vertebrate animals (as well as some invertebrates, including decapods and cephalopods), reflecting the fact that scientists are increasingly coming around to the view that while we may not be absolutely sure that fish can feel pain (and given the fact that they can’t tell us, we may never be sure), it might be best to give them the benefit of the doubt.