Fish Feel Pain
New Research on the Consciousness of Fish
The new review
Can fish suffer? This question comes up occasionally in discussions about animal rights. Scientific research should seemingly provide an answer to this question. Designated research on the subject is quite rare (in 2003 we reviewed one such research), but useful information can be derived from other research - much of which includes inflicting severe harm upon the fish. The most recent summary of the subject was published in June 2004 in the journal 'Applied Animal Behavior Science' by researchers from the Animal and Fowl Science Department at the University of Guelph (Ontario, Canada). Of the three researchers - Chandro, Duncan and Moccia, the name of Ian Duncan stands out, as he is one of the world's most prominent researchers in the field of animal welfare, and one of the only researchers to have systematically explored the question of 'What is Animal Welfare?'. Duncan's participation in the research guarantees the acknowledgment of interdisciplinary fields of research, from behavior to anatomy, which is often lost on researchers that focus on one particular field. The Guelph team reviewed and summarized 213 sources. We provide a summary of their research below, after simplifying some professional terminology included in it.
Welfare and Consciousness
If a fish is merely sick, it does not necessarily mean that its well-being is harmed. Harming its well-being entails a negative feeling, a conscious state. 'Consciousness' or 'sentience' are extremely tough to define, but for the time being, we are looking for more complex quality than the ability to respond automatically to certain stimuli or to undergo automatic conditioning with respect to them. In particular, we are looking for the ability to perceive different stimuli and flexibly combine between bits of data out of an active choice and an emotional state of motivation to act. While there is no way of directly perceiving such emotional states in others, it's possible to identify indications of them. According to the Canadian team, these indications include anatomical, physiological and behavioral sources, with a preference to the latter.
Fish Learn From Observation
Do fish react to environmental stimuli without thinking, as a reflex, or do they process information consciously? Few have examined this issue explicitly, but many behavioral experiments from previous studies have allowed us to apply the information revealed here. The most compelling experiments were conducted in recent years, and they indicated that fish (more specifically, bony fish) pay active attention to their surroundings, maintain interactive communication with external stimuli, recall prior experiences, compound the data stored in their memory with new information and demonstrate expectation with relation to future occurrences. One of the most interesting experiments mentioned by the Canadian team tested the ability of Siamese fighting fish to learn from observation. The researchers had placed one fish in one tank and allowed it to observe other fish fighting amongst themselves in another tank. When given the choice, the observing fish would avoid conflict with the victorious fish but confronted the losing ones. This observing fish acted less regularly when in an ensuing experiment it hadn't previously observed the fighting fish. Hence, the observing fish adjusted its behavior to its rivals not only based on its personal experience (i.e. trial and error, which may bring about conditioning) but also by observing other fish. Other experiments showed that fish learn about their environment by observing it (e.g.: females select males after watching their performance), then remember information and pass it on to each other. These data imply that fish process complex information in a flexible and adaptive way, or in other words, they appear to have consciousness.
Anatomical and Physical Resemblance
The nature of the relationship between nervous mechanisms and emotional states is under fiery controversy. However, there is no controversy over the fact that in many situations, emotions have a high survival value in comparison with reflexive reactions, and that emotions are in the product of relatively primitive brain structures. The Canadian team doesn't contend that the fish brain is identical to parts of the brain in other vertebrae (amphibians, reptiles, fowl and mammals). The assumption of resemblance is based not on a structural similarity but on homology- a functional resemblance between parts of the brain of fish and those of other vertebrates. One of the forms of proof most favored by vivisectionists is the removal of certain parts of the brain; such procedures reveal that the removal of parts of the brain in mammals brings about similar behavioral results to those following the removal of parts of the brain in fish. Electrical shocks also provoke similar reactions among the different groups. Thus, there seems to be a broad homology in the physiology of the brain in fish and in other vertebrae. Fish react to medication that affects the mind in a manner similar to mammals. Natural chemicals that are excreted by the nervous system and affect different behaviors and the transmission of pain, operate similarly in mammals and in fish, and their traces are apparent in certain homologous areas of the brains of fish and mammals. The injection of such chemicals into the brains of fish or dipping them in the chemical, caused a reduction in aggression, an improvement in memory, and even a Parkinson-like disease - all symptoms similar to those known from similar experiments in mammals.
The question isn't "can fish feel pain?", states an up-to-date researcher, but "what kind of pain do they feel?". The Canadian team concludes that the pain fish feel is similar to the pain experienced by other vertebrates. Different kinds of nerve fibers, which are known to transmit different types of pain in mammals, exist in fish. In fish, damaging these fibers provokes electrical activity in the nervous system - in the fish's brain and in the spinal cord. The information originating at the tips of the nerves undergoes a sorting process in the fish's spinal cord, much like in mammals, and sends sorted signals to areas in the brain that have been shown to play a vital role in avoiding harmful stimuli; it is therefore unlikely that the fish react to damage caused to the tissue by way of reflex only, through the spinal cord. The nervous systems of both groups exude identical chemicals that transmit signals of damage to the tissue, as well as chemicals serving as pain-killers.
Similarly to the pain manipulations described above, researchers have managed to prevent fish from demonstrating fear of dangerous stimuli in their environment by giving them medication used for suppressing fear in humans. The medication also caused the fish to demonstrate curiosity, similar to the effect it produced on rodents. The typical fear-induced reaction is prompt escape, which researchers have found changes according to the circumstances through learning. For example, fish changed their behavior toward an image of a predator once they learned that the predator won’t attack them.
One final issue that the Canadian team reviewed is distress resulting from social situations. Territorial fish establish social hierarchy through struggles, and each fish remembers its place in the hierarchy. A fish (or any other vertebrate) in a state of constant peril undergoes a variety of physiological reactions, which result in a surge of cortisol in the blood. By measuring cortisol levels and making behavioral observations, researchers have found that fish that are inferior in the hierarchy suffer from the presence of superior fish - apparently since they remember the superior fish and expect to be harmed by them.
The conclusion of Chandro, Duncan and Moccia is repeated time and again throughout their article: despite a want in data, the existing anatomical, physiological and behavioral data show that the probability that fish are sentient - that they feel fear, pain, hunger, thirst, joy etc.- is higher than the probability that they aren't. The consequences of this conclusion are clear: fish must be taken into consideration. For these researchers, suffice it to assert the need to investigate existing agricultural methods and improve them. But a more reasonable and morally coherent conclusion would be to avoid the consumption of fish altogether.