Do Fish Feel Pain?

Ila France Porcher posted the following as a rebuttal to a 2002 paper titled The Neurobehavioral Nature of Fishes and the Question of Awareness and Pain, Fisheries Science, 10(1): 1-38 by James D. Rose which asserted fish and sharks don’t feel pain. Rose’s paper can be downloaded on Google. Fisherman James D. Rose asserts 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. Thus, he claims that the required neurological machinery 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, and omitting consideration of the evolutionary pathways of the vertebrate brain, 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 had 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.

Evidently, cognition—the ability to think—was an important factor in the establishment of whether fish could feel pain, and it happened that in the same year as Rose's article was published, Bshary, Wickler, and Fricke published a review of the findings on the cognitive capabilities of fish (Bshary et al 2002). Here are a few examples:



Recognition of others as individuals has long been established in many varieties of fish, both visually and acoustically (Myrberg and Riggio 1985). It forms the first step towards complex social lives, in which cognition is often most evident. I documented relationships among reef sharks for years. They, too, relate to each other individually.

Social learning is illustrated by the migrations of the surgeon fish, Acathurus Nigrofuscus, described in detail by Arthur A. Myrberg Jr. in 1998. These fish leave their territories all over the lagoon, and travel in single file through paths in the coral to their traditional spawning grounds. They go and return along the same paths each night at precisely the same time, as I saw in the local lagoon, year after year. I had noted that the spawning ground was the only place along the lagoon's border where the outflowing current was exactly balanced by the incoming surge, so that the huge cloud of spawn that they left there, in the gathering night, stayed in place. These short term migrations had been shown to be the result of social learning; each generation of fish learned from its elders where to go to spawn, and when.

Triggerfish, Balistidae. often feed on sea urchins. Usually, they try to “blow” them onto their side to get access to the unprotected body parts beneath. Fricke (1971) observed at Eilat how five different individuals of Balistapus undulatus sucessfully hunted sea urchins by first biting off the spines, which allowed them to grab the urchin and take it to the surface. They fed on the unprotected parts underneath, while the urchin slowly sank. In spite of decades of observations, Fricke never saw this behaviour anywhere else. It appeared to be the result of social learning.

Intertidal gobies, Gobius soporator, live in tide pools, and during low tide they can jump from one to another, without being able to see their target pool at the beginning of the jump. Experimentation showed that the fish had memorized the lay of the land around the home pool by swimming over it when the tide was in, so were referring to a three dimensional memory to navigate when the outgoing tide left them only a labyrinth of pools. (Aronson 1951, 1956).

With the exception of humans, fish are more skillful than primates at nest building. At least 9000 fish species build some sort of nest, either for egg laying or for protection.

The male minnow Exoglossum selects more than three hundred stones, all of the same size, from over 5 m distance, to build a spawning mound 35 cm wide and 10 cm high (van Duzer 1939). Another fish builds dome-shaped nests from 10,000 pebbles (Lachner 1952).

The jawfish (Opistognathus aurifrons) collects stones of various sizes to build a wall, leaving a hole just big enough to pass through. This involves repeated rearrangement of the stones. In between, the fish searches for new stones that might better fit the available space than the ones it has already collected, using flexible behaviour depending on the circumstances (Kacher 1963; Colin 1972, 1973).

Another example showing surprising flexibility of behaviour is the ability of the ten-spined stickleback (Pygosteus pungitius) to build his nest around the eggs if the female has already laid them, though he usually builds the nest first (Leiner 1931). Great care is required, and a different technique has to be used to avoid damaging the eggs. Since those eggs do hatch, the males achieve their goal. (Morris 1958)

R. Bshary (2002), described seeing cooperative hunting between red sea coral groupers (Plectropomus pessuliferus), or lunartail groupers (variola louti), and giant moray eels (Gymnothorax javanicus):

“These two large species of groupers were observed regularly approaching the eels that were resting in a coral cave, and shaking their bodies in exaggerated movements, usually at less than 1 m distance to the moray eel.... In 7 of 14 observations, the moray eel left its cave and the two predators would swim next to each other, searching for prey. The groupers would often come so close that the two predators touched each other at their sides. While the moray eels sneaked through holes, the groupers waited above the corals for escaping fish.”

Another unusual form of cooperation among different species is seen in cleaning symbiosis. Cleaner fish come from many different fish families, and depend on cleaning for their diet to varying degrees. They clean the dead skin and ectoparasites from their clients in return for a meal. Full time cleaners may have about 2,300 interactions per day, with clients belonging to 100 different species! (Grutter 1995)

According to the evidence, cleaners have their hundred client species categorized as those who only come to their local cleaner, and those whose home ranges include the territories of other cleaners. For the latter, they have competition, so give them priority over the locals, who have no choice of cleaner.

Cleaners sometimes “cheated” by feeding off the client's healthy flesh as well as doing the usual cleaning job, and the clients with no choice of cleaner punished the cleaner by aggressively chasing it, and inflicting a bite or two, as they saw fit. (Clutten-Brock and Parker 1995). But these clients benefited in the future, because the cleaner fish were seen to give them, but not others who visited in the meantime, a better-than-average cleaning service on the next visit! Apparently cleaners can distinguish more than 100 individual clients belonging to various species.

Cleaners will hover above the client and touch it with their fins, in an effort to influence its decision to come for a cleaning. This touching tactic is also used to try to reconcile with a client whom they have cheated as described above. Cleaners even exploit the presence of a third party in an attempt to make aggressive clients stop chasing them by going to a nearby predator and caressing it, so that the client dares not continue the chase!

Cleaners will behave altruistically toward their clients if they are being watched by potential new clients—but only those who could visit another cleaning station. Since clients will emulate the behaviour of the former client, the sight of another being treated very well by the cleaner, is more likely to convince it to come for servicing than seeing another client being chased or eaten! This tactic suggests a short term image, or social prestige (Alexander 1987; Zahavi 1995; Nowak and Sigmund 1998; Roberts 1998), that determines their success in attracting new clients.

Such complex social behaviour—cheating, reconciliation, altruism, species recognition, individual recognition, punishment, social prestige, and bookkeeping, displayed by full- time cleaners 50 to 100 times per day, is generally considered to indicate consciousness when displayed in primates.

A similar example of social judgement is given by predator inspection, in which different individuals take turns to lead others away from the school to look over a predator. Fish who don't take their turn cooperatively, will not be trusted by their partners in the future. In other words, the fish make an evaluation of the behaviour of another individual, remembers it, and takes it into account in future decisions. (Milinski et al. 1990b; Dugatkin and Wilson 1993)

At the end of the review of cognition in fish, Bshary wrote: “We are aware of only one experimentally shown qualitative difference in mechanisms between primates and fish, and this difference is the ability to imitate.”

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 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, in our present time considerations). In reviewing the relationship between learning in fish, memories, and conscious cognition, Chandroo et al found an objective basis for suggesting 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 or other heightened states will over-ride pain, which is generated from deep in the brain. 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 would 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.

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 birds and mammals.

It is daunting, how many people are 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 atomic age.