Do cold-blooded (fish, reptiles) feel pain?

Answer

Best,

A very valid question to which there is no simple answer. Below some clarification about pain perception in (among other things) fish, something I recently wrote for a magazine of an aquarists association. In summary: fish do experience pain, if ‘pain’ is regarded as ‘a physiological reaction of the body as a result of a negative experience’.

Hopefully this clarifies a little

kind regards

Dominique Adriaens

“Whether or not considering ethical implications with regard to fish welfare often depends on whether one takes an anthropocentric and anthropomorphic perspective, especially when it comes to fishing and fish suffering. This results in different attitudes towards other creatures, in this An anthropocentric person considers fishing as something significantly inferior to man, so that ethical problems that apply to man would not apply to fish at all. An anthropomorphic person, on the other hand, will consider the ethically charged problems of man projecting onto fish and thus treating them as suffering organisms of equal value. However, both attitudes are subjective and extreme positions are wrong in both cases, which also makes it difficult to arrive at an unambiguous and correct position. Take the following quote from Aquarium World: ” .. especially the concept of “pain” is used from the human experience on the d extrapolated.” This quote refers to a commonly made anthropomorphic mistake, namely that those experiences that a person consciously experiences are consciously experienced in the same way by other organisms. Conscious sensations are generated in certain specialized regions of the brain, most notably the neocortex of the cerebrum. This neocortex evolved evolutionarily only from the mammals. And even then, self-awareness (the ability to experience pain consciously and emotionally, among other things) is a quality that is only assigned to humans, apes and dolphins (at least until now) (Allen and Trestman, 2017). Although animals can show reactions that clearly indicate pain, as one would expect in humans if this pain were experienced, it cannot automatically be concluded that those animals experience it in the same emotional way as humans do.

But here lies the pitfall, when the interpretation immediately spills over into an interpretation that is too anthropocentric. After all, it is wrong to assume that because of not consciously experiencing pain (so-called nociception), fish do not have any negative experiences at all as a result of pain and stress. There is no doubt that even in fish pain must be accompanied by a negative experience, because that is the whole evolutionary essence of pain: making sure that a certain experience that harms an animal is perceived as negative, so that the next time it is experienced as negative. experience will be prevented. Should pain be accompanied by a positive feeling, it is quite obvious that an animal would not survive that long (one does not hit the finger with a hammer again, because this was such a positive experience).

Although much less is known about the anatomical and behavioral aspects of pain perception in fish (compared to, for example, mammals), it is now clear that fish have all the essential parts for experiencing pain: sensory organs to receive it, nerve pathways to transmit it to the brain. brain, processing centers in the brain, chemicals to control pain, and behavioral responses to pain stimuli. More than 10 years ago it was shown that fish also have the specific nerve pathways that are responsible for the detection of pain stimuli, and that their stimulation gives rise to a pain response (and even a feeling of fear) in the animal (Ashley and Sneddon, 2008). In trout, for example, 35% of all sensory organs on the head consist of so-called nociceptors (sensory organs for detecting pain stimuli). As for the delivery of pain impulses to the brain, there are nerve pathways (both the very fine nerve fibers that pick up direct pain stimuli, and the larger nerves that send them to the spinal cord and brain) that are very similar to those found in mammals. Fish have parts in the front part of their brain (the telencephalon) that are analogous in function to parts of the human brain that are responsible for the sensation of pain and fear (e.g. amygdaloid zone in fish and the amygdala in mammals, or the thalamus which is connected to the brain zone where sensory stimuli enter). It has also been shown that the duration of certain behaviors associated with a painful stimulus is proportional to the intensity of pain elicited (a saline injection produces a shorter pain response than a bee venom injection). They also have a mechanism to reduce the pain after a painful stimulus (otherwise an animal would be in constant pain): they have certain molecules in their cells that can bind opium-like substances (these are substances produced in the body that cause pain). suppress). For example, a certain behavior that is associated with pain will disappear if an anesthetic such as morphine is administered (this also binds to those molecules). Although there are no demonstrable signs that a similar conscious and emotional sensation of pain is present in fish, as in animals with more complex brains, including humans (Rose, 2002), there are numerous indications that this should not be considered purely reflexive. be considered (Ashley and Sneddon, 2008; Huntingford et al., 2006). For example, fish, including goldfish, can be taught to avoid harmful stimuli, indicating a certain complexity of thinking and learning.”