Kenneth Kidd: That must be painful. Or not
Do fish feel pain?
It sounds like a simple question, one that ought to have a simple, yes-or-no answer — the kind we humans tend to crave. But if there's a query that manages to combine uncertain science, definitional problems and occasionally blind emotion, it's this one.
For a start, even language can get us into trouble. At least in popular Western culture, we have a long history of attributing human motives and emotions to all manner of animals and insects.
It shows up in the bedtime stories we read to our kids and the animated movies we see at the cinema. It's as if humour, shame, pride and sorrow are all part of everyday life in nature, felt and understood by animals in precisely the same way they are by humans.
Lacking other words to describe animal behaviour and motivations, we simply use the ones that would apply to us. That has obvious literary benefits, but does it lead us astray in science?
James Rose, a professor of zoology and physiology at the University of Wyoming, certainly thinks so.
"Animals often do things that resemble things that we do," he says. "But it's a very different matter to interpret that (as meaning) they're thinking and planning what they're doing."
That's especially problematic with animals, like fish, that followed a different evolutionary path than humans, endowing them with brains and neurological systems far different from our own. For Rose, fish just don't have the necessary mental equipment to think about and feel pain in the way we do.
"If you look at fish in general, their brain stems are highly developed, but the cerebral hemispheres are not highly developed," he says. "They have the rudiments of what we have, but it just isn't very expanded, and everything I know about things like awareness indicate you've got to have more brainpower upstairs than they have."
In recent years, however, there has been a lot of debate on the pain issue, including a symposium last week at the University of Guelph that featured Victoria Braithwaite, one of the co-authors of a recent (and controversial) British study.
Braithwaite's group looked at the heads of trout and identified two types of so-called nociceptive nerves: A-delta fibres and C fibres.
In mammals, A-delta fibres are associated with perceiving instant stimuli (like hitting your thumb with a hammer), and C fibres give you the lingering sense of injury (the subsequent throbbing).
Roughly half of the nociceptive nerves in mammals are C fibres, but in fish that number is typically only four per cent. And some, like sharks, don't have any, so they simply can't detect what we'd recognize as long-term pain or a sense of injury — which probably helps explain why sharks are such ferocious biters, and why their stomachs often include everything from car mufflers to anchors.
To see whether those nociceptors were working, Braithwaite et al. injected trout with noxious substances (acetic acid or bee venom), and then watched how their behaviour changed. Depending on the experiment, the trout lost their appetites for a time, started beating water through their gills more frequently, or rubbed their noses on the side of the tank.
The study's conclusion: Those nociceptors were doing their job and the fish were reacting to pain.
But were they? Or was it just an unthinking reflex in the face of a negative stimulus?
"I would say they can certainly perceive pain," says Braithwaite, a senior lecturer in evolutionary biology at the University of Edinburgh. "Whether they feel it as an emotion, I would think they probably do."
This is where the definitional problems come in. What exactly is pain? Is it just any negative stimulus, or does the experience of pain require a higher consciousness, including self-awareness, memory and the ability to think and plan?
Academics can spend a lot of time debating the precise nature of "consciousness," but from a clinical, neurological perspective, instinctive reflexes aren't part of the mix.
"It's not just the ability to perceive and react to negative stimuli," says Richard Moccia, a professor of animal science at Guelph. "That isn't pain. Pain really is psychological at a higher level. We're really thinking about a higher level of consciousness being required."
And do fish have that consciousness? "The jury," says Moccia, "is still out on that."
Even Braithwaite, who readily uses words like pain and fear when talking about fish, isn't sure they're conscious.
"I would say that some of the behaviours of fish are much more sophisticated than we would have given them credit for, say, a decade ago," says Braithwaite. "Whether that means they're conscious, I feel very uncomfortable about. I would say we don't have enough evidence to say that they are."
There is, on both sides of the issue, fairly wide agreement that too much cognitive ability might actually be a very bad thing for a fish, since taking time for thought could prove fatal.
"They've got to be vigilant all of the time, whether they're a predator or prey," says Rose. "I've watched bonefish and sharks interact in the Bahamas, and everybody's got to pay attention all the time, because when a shark takes off, it's pretty abrupt."
So why, then, this renewed interest in whether fish experience pain? It all has to do with fish farming, which has lately come under attack by some animal-rights groups, especially in Europe.
And if you want fish farming to be governed by the same sort of rules that have long applied to the treatment of traditional farm animals, then it's more than a little helpful to have fish considered as being not much different than cattle or sheep.
As Braithwaite puts it: "The problem we have with fish is that they have this reputation of being cold-blooded, dim-witted creatures. People who do work with fish tend to think, oh well, you know, they're fish, it doesn't matter.
"We needed to say, well, actually, they're not that different from mammals and birds, because they have the same pain-processing equipment that we associate with animals."
The claimed existence of pain, in other words, might help ensure that farmed fish are treated and killed humanely. So, yes, there is an agenda.
But do we really need unchallenged evidence of pain — and consciousness — to make us act humanely?
Gary Varner, an ethical theorist and philosophy professor at Texas A&M University, argues we don't need to go quite that far. "It's not as if one finding is going to come in and carry the day."
All you need to make is a so-called argument by analogy, he says. If X has these 10 characteristics and Y has nine of them, chances are Y also has the tenth. From a philosophical perspective, you end up treating farmed fish as if you knew for certain they experienced pain, despite the lack of scientific proof.
This would, at any rate, work out better for the fish — and might even be preferable to harvesting them from the ocean.
"The only vertebrates I eat are fish," Varner says. "When I'm out fishing and I hook a fish, I do my best to kill it quickly, but maybe that could be better done under more controlled conditions. It wouldn't surprise me at all if fish farming, at least in ideal conditions, turned out to be a far better way to raise and harvest fish."
