Pain in Fish : a review of the evidence

Fisherman James D. Rose claims that fish can't feel pain. He has published a paper stating that the neocortex, the outer folded layer of the brain that is so highly developed in humans, is the seat of all higher mental functions, including consciousness of pain. Therefore, the neurological machinery required to feel pain is missing in a fish, and indeed, is present only in humans and apes. But, in focusing on a comparison of the human brain with the fish brain alone, Rose's article seems biased and anthropocentric.

Rose did not give a reason for his assertion that consciousness depends, alone, on the neocortex. Nor did his argument take into account the straightforward evolution of the vertebrate brain. From fish to man, the brain has the same structures, arranged in the same way, with the exception only of the neocortex, which developed in mammals. Neurological studies have shown that the newly evolved neocortex of mammals took over certain higher functions, which were already present in fish, amphibians, reptiles, and birds. (I. Glynn 1999)

The expansion of the forebrain has occurred many times in different species, including in some fish, whose brain structures would fall into Rose's category. All teleost fishes (bony fishes) have elaborate forebrains (Butler and Hodos 1996) and the degree of forebrain development has been correlated with social behaviour, and communication abilities, which are considered to be integrated with cognition. (Kotrschal et al 1998).

Fish continue to develop neurons throughout their lives, and do so at a faster rate when confronted with a stimulating environment, indicating a link between experience and neural development. For example, the triggerfish, (Balistidae), which have advanced foraging techniques, have a relatively larger telencephalon—the front part of the forebrain—than most other families of fish investigated (Geiger 1956).

It is well established, for example, that birds feel pain, and have advanced cognitive abilities. Some species have better long term memories than humans, and others far exceed us in visual recognition. Yet their little pea-brains lack a neocortex. The miniaturization of the animal did not affect mental capability (Barber 1993). Tests with birds showed that higher mental capabilities could be found in a brain that is wired differently than ours. Dolphins, too, show high cognitive capabilities, but their brains have a different form than primate brains, though both are mammals (Marino 2002). There are people in which the expanded neo-cortex failed to develop, but who have normal psychology and IQ's. (Edelman and Tononi 2000). So even in humans, it seems that the neocortex is not necessary for consciousness.

Other researchers have concluded that the neocortex was not central to consciousness. Donald R. Griffin, (1998) theorized that the expanded human brain had allowed the appearance of a complex subconscious mind. Since consciousness was more likely to have been favoured by evolution due to its value for survival, he considered it more probable that the centralization of the nervous system had resulted in consciousness. No brain is simple, as anyone who has observed the activities of a spider will appreciate.

Laureys et al (2000), and other researchers, found evidence that the thalamocortical system was the essential neurological basis of conscious awareness, and Chapman and Nakamura (1999) concluded that the neural systems involved in the detection of tissue damage, (nociception) and the awareness of the pain, likely evolved as an “interactive dynamic system” with the cognitive processes, in the evolving central nervous system. These findings and others suggested that it is the way the various regions of the brain are integrated, that generates consciousness.

All of this easily available evidence that contradicted Rose's conclusions, was omitted in his article. He seemed to rely on the beliefs of fishermen, that the fish brain was so simple that it was well understood, and that it could not support consciousness. Unfortunately, fishermen had given it so much publicity that people remembered only that science had proven that fish don't feel pain. Some people started claiming that fish were missing part of their brains!

Rose ascribed Pavlovian learning, only, to fish, denying any possibility that consciousness could be involved. Other researchers found evidence that showed otherwise, and denied that learning in fish takes place in the total absence of cognition and consciousness. (Maren 2001, Lovibond and Shanks 2002; Overmier and Hollis, 1990). Chandroo et al (2004), acknowledged that learning processes seen in fish, “may require the formation of declarative memories.” (Declarative memories are memories of facts, which we can call on to use, consciously, at any time). In reviewing the relationship between learning in fish, memories, and conscious cognition, Chandroo et al found that some fish behaviour is better explained within a theoretical framework that includes primary consciousness.

Fishermen will claim that fish don't feel pain, because they have seen sharks continuing to function in spite of terrible wounds. However, this is a common behaviour even in humans. Fear is generated from deep in the brain and will over-ride pain. The effect has an obvious benefit for survival.

Another argument declare that fish cannot feel pain because sometimes a fish will bite a baited hook a second time, after being unhooked and thrown back into the sea. But, while it may be obvious to the fisherman what he is doing, how could it be obvious to the fish? These men assumed that the fish understood much more than it possibly could about its situation. It could have no basis, among its experiences in life, for understanding the fisherman's practice of deception—the possibility of a hook hidden in the bit of food it had found.

It can see no dangerous predator underwater, so how could it imagine that above the surface a man is waiting, hoping to trick and kill it? Even a human walking by the sea pursuing his own affairs, would never suspect that there was a creature waiting for him beneath the surface with a plan to trap and kill him. A fish that had already bitten a bit of food with a hook in it, has no reason to assume that the next piece of food it finds will also hide a hook.

But why ask those whose only interest in fish is to kill them? There are people who have good will towards fish : veterinarians. A bird specialist in Australia, Dr. Pat Macwhirter, wrote to me that she had assisted in surgery on a fish when a fish vet had come to work at her animal hospital. She described the fish being more sensitive than birds to electro-surgery, and said that the anaesthesia had to be deepened. There was no doubt, she told me, that the fish had felt pain.

With their training in healing, and experience with distressed animals, it seems to me that veterinarians are in a much better position than fishermen to judge whether or not an animal is in pain. I too had noted that the sharks who had escaped being landed for finning, as well as female sharks with extensive mating wounds, showed similar signs of pain as other classes of animals. They were less alert, less reactive, and slower moving.

Temple Grandin and Mark Deesing at the American Board of Veterinary Practitioners Symposium of 2002 declared that “the ability of an animal to suffer from pain may be related to the amount of associative neural circuitry linking sub-cortical structures to higher levels of the nervous system.” They considered that one could assume that an animal was in pain if it actively sought pain relief, protected injured parts, became less active when sick or injured, or self administered pain killing drugs, all of which are seen in fish, whose bodies release strong analgesics, which relieve pain.

The work of Dr. Lynne Sneddon, at the University of Edinburgh revealed 58 receptors located on the faces and heads of trout, that responded to harmful stimuli. They resembled those in higher animals, including humans. A detailed map was created of pain receptors in fish's mouths and all over their bodies.

Dr. Sneddon injected the lips of trout with acetic acid, bee venom, or saline solution as a control, and found that those injected with the noxious substances showed symptoms of pain, including an accelerated respiratory rate, rocking back and forth on their pectoral fins, rubbing the affected areas on the substrate, and taking longer to resume feeding than the control group, whose behaviour remained normal. A morphine injection significantly reduced these symptoms. (Sneddon, 2003)

The relief of the fishes’ symptoms by the pain reliever shows the interconnection between the nociceptors, which sense the tissue damage, and the central nervous system. Here was proof that fish are aware of tissue damage as pain.

Other researchers published papers showing that fish vocalize when they feel threatened. I too, have found that when I stroke triggerfish hiding in a cavity in the coral, it squeaks at precisely at the moment of each caress.

Rebecca Dunlop of the Queens University of Belfast, found that fish learn to avoid pain. She said: “Pain avoidance in fish doesn't seem to be a reflex response, rather one that is learned, remembered and is changed according to different circumstances. Therefore, if fish can perceive pain, then angling cannot continue to be considered a non-cruel sport.”

When told of these findings, James Rose replied: “One consequence, at least where I live, is that all the revenues that support research on the habitat of fishes, that monitor the health of the fish populations here—all the biologists who do this work are funded by (fishing) licence revenues. If there was no fishing there would be no one to do their job. That would be a catastrophe. That would be a colossal loss, and believe me, there would be no other funds from other sources to do the same job.” (James D. Rose speaking to science reporter Abbie Thomas, the producer of “All in the Mind,” at ABC)

This seemed a further indication that his paper allegedly proving that fish don't feel pain was politically motivated rather than an honest desire to find out the truth. Note that he had done no study, as Dr. Lynne Sneddon did, to determine whether fish feel pain or not. He had simply declared that a difference between the human brain and the fish brain proved that fish can't feel pain, while ignoring other relevant evidence.

And it can be argued that research by and for sport fishermen is of questionable ultimate value since it focuses only on the target species, to the neglect of the others in the aquatic community, and is conducted in hope of favourable results for a political cause. 

Sneddon's results have been found since by other researchers who have further investigated the best way to relieve pain in fish during surgery. (Harms et al. 2005) Pain relief is now systematically used by veterinarians who perform surgery on fish, in the full belief that they feel pain. It is now believed that the pain system in fish is virtually the same as in mammals.

It is daunting, how many people remain proud of their efforts to outwit fish. They don't see the irony in claiming that fish are too simple to feel pain, while being proud of their ability to outwit them. This appears to be the mindless acceptance of a tradition, resulting from a discovery in the stone age, and, incredibly, still bragged about in the computer age.

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