An international team of researchers have determined that fish do not feel pain the way humans do.
This team of neurobiologists, behavioral ecologists and fishery scientists were led by Prof. Dr. Robert Arlinghaus of the Leibniz Institute of Freshwater Ecology and Inland Fisheries and of the Humboldt University in Berlin. The results of their study can be found in a recent issue of Fish and Fisheries.
This study has far reaching implications in Germany. On July 13th of this year, a revised animal protection act was enacted. However, it does not contain any concrete statements regarding the handling of fish. According to the protection act, fish are sentient vertebrates who must be protected against cruel acts performed by humans against animals. This means that anyone in Germany who kills or inflicts severe pain or suffering on vertebrates, without due cause, faces penal consequences, including stiff fines and prison sentences.
Before the revised act, the legislature had settled the question of the fish issue, but the revision opened the door again to the question of how fish feel pain. A final answer will have far-reaching consequences for fishers, anglers, aquarist, fish farmers and fish scientists.
The research team, consisting of seven specialists from the USA, Europe, Canada, and Australia, has performed a literature review of all the significant studies on the subject of fish pain in order to answer this question. They identified many deficiencies in the studies. Chief among these are the assumption that fish do not have the neuro-physiological capacity for a conscious awareness of pain, and that behavioral reactions by fish to seemingly painful impulses were evaluated according to human criteria and were thus misinterpreted. Thus, they have determined that there is still no final proof that fish can feel pain.
It is necessary to understand how pain perception works for humans to comprehend the researchers’ criticisms. In humans, injuries stimulate nociceptors, which send electrical signals through nerve-lines and the spinal cord to the cerebral cortex, or neocortex. This is where the signals are processed into the sensation of pain if the person is fully aware.
Not all injuries, even severe ones, necessarily result in an experience of pain, however. For example, pain can be intensified through causing fear, and it can be mentally constructed without any tissue damage at all. In other words, our mental state affects our feeling of pain. It is also possible for any stimulation of the nociceptors to be processed without the person having an experience of pain. This is the principle upon which anesthesia works.
Because of these challenges, pain research distinguishes between a conscious awareness of pain and an unconscious processing of impulses through nociception. This unconscious processing can also lead to hormonal reactions, behavioral responses as well as to learning avoidance reactions. This means that nociceptive reactions cannot be equated with pain, and are not a prerequisite to pain.
Fish, unlike humans, do not possess a neocortex. This fact provides the first indicator of doubt regarding the pain awareness of fish. In mammals, certain nerve fibers known as c-nociceptors have been found to be involved in the sensation of intense experiences of pain.
The study looked at two classes of fish: primitive cartilaginous fish such as sharks and rays, and bony fish such as carp and trout. The primitive cartilaginous fish show a complete lack of c-nociceptors, and the bony fish rarely present them. This means that the physiological prerequisites for a conscious experience of pain are hardly developed in fish. Bony fish, however, do possess simple nociceptors, and do show reactions to injuries and other interventions, but it is not known if this is perceived as pain.
The current study finds that there is often a lack of distinction in the literature between conscious pain and unconscious nociception. The majority of research reviewed by the team evaluates a fish’s reaction to a seemingly painful impulse such as rubbing the injured body part against an object or the discontinuation of the feed intake as an indication of pain. This methodology, however, does not provide verifiable proof that the reaction was due to a conscious sensation of pain or an unconscious impulse perception by means of nociception, or a combination of the two.
It is very difficult to use behavioral responses to detect underlying emotional states. In addition, fish often show only minor or no reaction at all to interventions which would be extremely painful to us and to other mammals. Pain killers that are very effective in humans, such as morphine, are ineffective in fish, or required such astronomically high doses that, for small animals, would have meant immediate death from shock. The researchers say that this finding suggest either fish have absolutely no awareness of pain in human terms, or that they have completely different reactions to pain. It is not advisable, therefore, to interpret the behavior of fish from a human perspective.
According to the German Animal Protection Act, it is forbidden to inflict pain, suffering or harm on animals without due cause, but the criteria for when such acts are punishable is exclusively tied to the animal’s ability to feel pain and suffering. The research team has serious doubts that fish are aware of pain as defined by human terms. In a strictly legal sense, this means it should not constitute a punishable offense if, for example, an angler releases a harvestable fish at his own discretion instead of eating it. The researchers stress, however, that their doubts about the ability of fish to feel pain do not release anybody from their responsibility of having to justify all uses of fish in a socially acceptable way and to minimize any form of stress and damage to the fish when interacting with it.
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