I’ve always figured that all animals – big, small, ugly – could feel pain. It makes sense that every creature should be able to detect horrible stimuli in order to quickly move away from it. Whilst this feeling of “pain” may not be as complex as the human experience of pain, it is still “pain” – isn’t it?
Well, it’s very difficult to objectively study pain in humans – let alone cows, mice or fish. The best evidence we have is looking at how animals react to potentially painful stimuli, like heat and bee venom, and seeing if their reaction is similar to how humans behave. These days we can also look at the neurons firing in animal’s brains to see how it responds to this stimuli, and again compare it to the patterns that neurons fire in humans.
From observations of cows headed to the abattoir, mice exposed to searing heat, and even pet dogs who hurt themselves, western society seems pretty comfortable with the idea that mammals can feel pain on a similar level to humans. Studies of “pain sensitive” regions in rat brains, and mice genetically engineered not have genes that transmit pain, also supported this conclusion. But, more controversial is whether fish feel pain.
In 2003 researchers from the Roslin Institute in Scotland found that when the lips of rainbow trout are injected with bee venom or acid they behave similar to how humans would. For example, the fish started “breathing heavily” i.e. the rate of gill breathing was similar to a fish swimming fast. And they took 90 minutes longer to start feeding again when compared to fish injected with harmless saline. The fish also rocked from side to side, a repetitive behaviour seen in unhealthy zoo animals. And, when injected with acid, they rubbed their lips on the side and bottom of the tank, just like humans might to reduce the pain from a burn.
The Scottish researchers say this sort of behaviour isn’t just a reflex – they are feeling some discomfort and attempting to alleviate it.
The fish’s neurons did funny things too. When injected with the venom or acid around 20 neurons in the trout fired in a similar pattern to that seen when humans feel pain. This didn’t happen when the trout were injected with saline.
Does this mean the fish feel pain?
Not necessarily. While the fish might be behaving as if they feel pain and some extra neurons are firing, it’s still very possible they just don’t have emotional capacity to percieve the stimuli as “pain” per se. That’s what fish neurobiologist James Rose at the University of Wyoming thinks. He reckons rhose extra neurons are just firing as a response to a new and unexpected substances. So, considering fish are renown for their short memory span they might just be thinking – “What’s that?” “What’s that?” rather than the complex emotion of “OUUUUUCHHH.”
Until the fish in Walt Disney’s Finding Nemo start translating to english, I guess, we’ll never know for sure if fish feel pain. But, the more we learn about animal behaviour, the more we seem to realise how similar humans are to the rest of the animal kingdom.
Notions that humans, or even mammals, are the only creatures to feel pain seems to hark back to theology – that we two legged, (mostly) hairless creatures, are somehow special and different. Pain is such an innate feeling, all creatures must feel it on some level, right? On the other hand, the human brain is pretty special, so it’s likely we can do and feel a whole lot more than a trout; maybe feeling pain is one of those things.
