Fish lack the brains for pain

THE debate to whether fish feel pain has raged for many years, however Professor Brian Key from the University of Queensland says it’s time to put the argument to bed for good.

Image: Scott Thomas

ANY successful angler knows that when a big fish takes your hook then you better hang on to your rod. That fish is going to flee. In the world of science this behaviour is called an escape response. Fish have evolved this powerful survival mechanism over hundreds of millions of years. Angling would not be the same if fish instead cleverly swam towards your rod. The escape response is automatically generated by the nervous system and the underlying circuitry has evolved because it was more likely that swimming away from a predator leads to a better chance of survival and hence ability to reproduce.

Humans have also evolved similar automatic responses. If you accidently touch a hot grill you will instinctively withdraw your hand. This response is so fast that it is done before you feel any pain at all. Pain comes slightly later; this is because the circuitry that causes pain is longer than the circuitry that generates immediate withdrawal/escape. The escape circuitry is in the spinal cord and rear end of the brain while the pain circuitry is in the front end of the brain and hence signals take longer to get there and to subsequently process. It is similar to having a light switch in the back room of your house that turns on a light in that room as well as a television in the front room of the house. When you activate that switch then the back room light will turn on almost instantly but it will take more time before you hear the sound coming from the front room television.

Many people think that because a fish flees it must feel pain. However, pain requires very sophisticated circuitry in the front end of the brain (just like a television has more complicated circuitry then a light bulb circuit). This pain circuitry is missing from the fish brain (although it is present in many other vertebrates, including: mice, dogs, cats, monkeys and humans). This lack of circuitry was confirmed when scientists surgically removed the front end of the fish brain. They discovered that these fish swim and eat normally, evade capture from a fish net as effectively as normal fish and display the normal rapid escape response.

Some people find it hard to understand why fish have not evolved pain when it seems so beneficial to other animals for survival. There are two pertinent points here. First, not all animals can or do evolve the same characteristics. Second, fish are not alone in lacking the necessary brain circuits to feel pain. There are many more species in the animal kingdom that lack, rather then possess this circuitry. It may be developmentally impossible for some species to evolve the successful characteristics of other species. Also, what may appear to be beneficial for one species may have no value for survival for another species in a different environment.

So the next time you are asked if fish feel pain then the answer is clearly no. Fish simply lack the brains for it. If you are tantalised by these ideas and want to further explore them then I suggest you pick up April’s issue of Australasian Science magazine at your local news agency and read the article “Do fish feel pain?”

Professor Brian Key is head of the Brain Growth & Regeneration Lab, School of Biomedical Sciences, at the University of Queensland.

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