Scientists can't decide if fish feel pain

Have you ever gone fishing? Did you keep the fish and eat it? Or did you pull the hook out and toss it back into the water?

The second option, catch and release, has always felt a little...wrong...to me.

Picture this: You're a fish. You're swimming along. You see a tasty worm, and chomp. BLAMMO! You're arching through the air, tugged by your mouth into the hands of some giant, overall-clad land-monster.

At this point, as a prey animal, you know what comes next. A sharp stab, a warm trickle, and then unfeeling, endless oblivion. You make your peace.

But then, imagine the big ugly human just plays with you for a few minutes while you gasp, unable to breath. Then there's a yank and your lip splits further (OW!) and you fly, splat, back to the blue deep. You think 'What the heck?' and then realize it's over and swim away. You're relieved, but still, what a jerk!

So fishing to eat makes sense to me. Catch and release? More like trout-bullying.

But the December 2016 issue of the journal Animal Sentience suggests that my moral intuition may be based on a fallacy: that catching a fish hurts the fish. You see, for a fish to hurt, it has to be able to feel pain.

The neurobiologist Brian Key, writing under the succinct title "Why do fish not feel pain?" lays out a compelling case that our finned, gilled, and scaled cousins simply don't have the brain structures to feel pain.

Human pain, he argues, happens in the cortex. That's the region of your brain associated with complex, conscious experience and thought. It's a complex system (even for a brain system), with a great deal of back-and-forth flow of information.

What does that mean?

The cortex doesn't just turn a stimulus, like a prick of the thumb, directly into an action, like yanking your hand away. That would be a one-way flow of information. Stimulus-reaction.

Instead your cortex turns the sensation over. What did that feel like? It hurt. Who did it to me? That fool. What am I going to do? Prick him right back when he least expects it. Ha ha! Stimulus-experience-consideration-reaction.

Fish certainly react to things that would be painful to people, swimming or flopping to avoid them. But they lack cortices, or any other structures in their brain that might do the multi-directional pain-processing job of the cortex. Key argues that without a cortex a fish can't feel the pain. Any behavior that looks like pain avoidance is really just the result of simple one-directional mental processes. Stimulus-reaction. Prick-flee.

Key points out that you can do things to a fish that would seem painful to a human eye, like drilling a hole in its head, without significantly impacting its behavior. You'd think that if a fish felt that overwhelming pain, it might find the experience a bit distracting.

He goes on to argue that a whole set of behaviors and experiences some researchers attribute to fish (anxiety, depression, discomfort, and so on) are really simple learning and avoidance that don't require any conscious thought.

That humans see so much complexity in fish, in his view, seems to say more about the people than the fish.

He can't prove that fish don't feel pain without actually living as a fish, he acknowledges, but science doesn't offer us any reason to assume they do.

Here's the thing though: Key's view isn't particularly popular among many of his colleagues.

Hanna Damasio and Antonio Damasio, a team of neuroscientists whose work on pain in humans Key cites in his paper, wrote one of several commentaries picking apart his argument.

Though they don't study fish pain, they write that Key is too simplistic in locating human pain entirely in the cortex. Yes, pain is more complex than the mere reflex that drives many simpler creatures through the world. And it is more difficult to figure out whether people without functioning cortices experience pain.

But there's real reason to think they do, or at least experience some of the unpleasant feeling-set we call "pain," because of processes in other regions of the brain, like the brain stem. Fish may not have cortices, but they certainly have brain stems.

There may not be enough evidence to prove fish feel pain, but Hanna Damasio and Antonio Damasio argue that Key doesn't marshal nearly enough evidence to show that they don't.

Some of Key's other critics are more pointed. Culum Brown, a biologist who studies fish behavior, writes a commentary that amounts to a long list of critics who reject Key's perspective.

I'd argue that the take away for us lay people isn't "it's totally cool to bully cod." But there is reason, as Key points out, to question our intuitions when we suggest (for example) that certain fishing behaviors should be banned.

At what point are we taking reasonable steps to protect animals from harm, and at what point are we making it harder for people to live because we're squeamish about some scientifically squishy inferences from thrashing fish?

Another takeaway? Consciousness, feelings, and experience are still concepts that science doesn't have a very good system for dealing with, especially when we're probing beyond the human mind. That's why both Key and his critics' arguments boil down to Look how much you don't know, and can't prove, not look at what I can prove.

There are no universally-accepted fundamental laws yet, or even that much in the way of common intuitions. The apple hasn't dropped on the head of consciousness studies' Isaac Newton. In the meantime, we're going to have to live without a definite answer about what happens in the mind of a hooked fish.