If you were a fish, you'd want to drag a hook through the mouths of humans and pull them into the water to drown

That Fish You Caught Was in Pain
Research challenges the myth among anglers that fish can't feel pain from barbed hooks.
By Victoria Braithwaite

Every year, sportsmen around the world drag millions of fish to shore on barbed hooks. It's something people have always done, and with little enough conscience. Fish are … well, fish. They're not dogs, who yelp when you accidentally step on their feet. Fish don't cry out or look sad or respond in a particularly recognizable way. So we feel free to treat them in a way that we would not treat mammals or even birds.

But is there really any biological justification for exempting fish from the standards nowadays accorded to so-called higher animals? Do we really know whether fish feel pain or whether they suffer — or whether, in fact, our gut sense that they are dumb, unfeeling animals is accurate?

Determining whether any type of animal really suffers is difficult. A good starting place might be to consider how people feel pain. When a sharp object pierces the human body, specialized nerve endings called nociceptors alert us to the damage. Incredibly, no one ever seems to have asked before whether fish have nociceptors around their mouths. My colleagues and I in Edinburgh, Scotland, recently looked in trout and found that they do. If you look at thin sections of the trigeminal nerve, the main nerve for the face for all vertebrates, fish have the same two types of nociceptors that we do — A-delta and C fibers. So they do have the necessary sensory wiring to detect pain.

And the wiring works. We stimulated the nociceptors by injecting diluted vinegar or bee venom just under the skin of the trout. If you've ever felt the nip of vinegar on an open cut or the sting of a bee, you will recognize these feelings as painful. Well, fish find these naturally irritating chemicals unpleasant too. Their gills beat faster, and they rub the affected area on the walls of their tank, lose interest in food and have problems making decisions.

When I have a headache, I reach for the aspirin. What happens if we give the fish painkillers after injecting the noxious substances? Remarkably, they begin to behave normally again. So their adverse behavior is induced by the experience of pain.

But just because fish are affected by pain, does that mean they actually feel it? To answer that, we need to probe deeper into their brains (and our own) to understand what it means to feel pain.

To determine what fish go through mentally when they experience painful stimuli, we also need to determine whether they have a capacity to feel emotion and to suffer.

This is a much harder problem. It goes to the very heart of one of the biggest unresolved issues in biology: Do nonhuman animals have emotions and feelings? Are nonhuman animals conscious?

Scientists and philosophers have long debated consciousness and what it is and whether it is exclusively human. There are multiple definitions and, frankly, we haven't really come to grips with what it means to be conscious ourselves. Are we conscious because we are capable of attributing mental states to others, or perhaps because we have a qualitative awareness of feelings, whether positive or negative? And if we can't define our own consciousness, can we expect to detect it in fish?

Perhaps not, but we can look for behaviors and abilities that we believe contribute to human consciousness — for example, complex cognitive abilities and specialized brain regions that process emotion and memory.

It turns out that the stereotype of fish as slow, dim-witted creatures is wrong; many fish are remarkably clever. For example, they can learn geometrical relationships and landmarks — and then use these to generate a mental map to plan escape routes if a predator shows up.

And their brains are not as different from ours as we once thought. Although less anatomically complex than our own brain, the function of two of their forebrain areas is very similar to the mammalian amygdala and hippocampus — areas associated with emotion, learning and memory. If these regions are damaged in fish, their learning and emotional capacities are impaired; they can no longer find their way through mazes, and they lose their sense of fear.

None of this tells us that fish are conscious, but it does demonstrate them to be cognitively competent: They are more than simple automata.

So do we have to change the way we treat fish? Some still argue that fish brains are so less well developed than those of birds and mammals that it isn't possible for fish to suffer. In my view, that case is not proven.

Moreover, we actually have as much evidence that fish can suffer as we do that chickens can. I think, therefore, that we should adopt a precautionary ethical approach and assume that in the absence of evidence to the contrary, fish suffer.

Of course, this doesn't mean that we necessarily must change our behavior. One could reasonably adopt a utilitarian cost-benefit approach and argue that the benefits of sportfishing, both financial and recreational, may outweigh the ethical costs of the likely suffering of fish.

But I do find it curious that it has taken us so long even to bother to ask whether fish feel pain. Perhaps no one really wanted to know. Perhaps it opens a can of worms — so to speak — and begs the question of where do we draw the line. Crustacean welfare? Slug welfare? And if not fish, why birds? Is there a biological basis for drawing a line?

(Victoria Braithwaite, a behavioral biologist at Edinburgh University, is on sabbatical at the Institute for Advanced Study in Berlin.)