The secret lives of fish

The study of fish cognition only gained full momentum in the beginning of this century, and new information is constantly being learned. A large part of the behaviour of wild fish is based on what the individual has learned.

During the past few decades, the study of animal cognition has progressed faster than ever before. At the same time, it has begun to find answers to questions that some in the scientific community used to believe were impossible to study. An animal’s subjective experiences and feelings are one such issue.

Some researchers of human cognition and psychology formerly assumed that humans were the only species which consciously experiences feelings and sensations. This was based on the hypothesis that feelings require the kind of large and complex neocortex only found inside a human head.

Basic emotions, such as happiness and sadness, were known to be generated by the limbic system, which is structurally similar in humans and other animals. 

However, we now know that cognition and emotions are two separate things, also on a structural and operative level in the brain. The size of the neocortex helps determine the ability for rational logic. Meanwhile, the conscious experience of emotions generated in the limbic system is not dependent on the size of the animal's neocortex – or even on whether it has a neocortex to begin with.

For example, birds have a structure in their brain known as the nidopallium instead of a neocortex. Despite their differences in appearance, it has since been found that the nidopallium functions very similarly to the mammalian neocortex.

An even more recent discovery is that the telencephalon in the brain of fish also seems to have a function similar to our neocortex.

We share fear and pain

Many of the neuroscientific discoveries relating to animal brain function are so recent that they have not made their way into the textbooks yet. One step towards disseminating these research results was made in 2012 when a group of top neurophysiologists, neuroanatomists, cognitive neuroscientists, as well as other researchers specialising in the function of the brain and the nervous system, attended the Francis Crick Memorial Conference held at the University of Cambridge.

The goal of the conference was to come to a consensus on what is known about animal consciousness and feelings based on brain research thus far. The participants signed the Cambridge Declaration on Consciousness, which states that the absence of a neocortex does not appear to preclude an organism from experiencing affective states, and that brain structures that generate consciousness exist in many mammals, birds and other animals in addition to humans.

Vertebrates – mammals, birds, reptiles, amphibians and fish – have proven to be much more alike in many ways than was previously thought. Evolutionary biology has for decades renounced the idea that vertebrate evolution can be described as a “ladder”, in which some species are “lower” while others are “higher”. Instead, our evolutionary family tree is more similar to an extensive, sprawling bush, in which all of the species alive today inhabit the outermost tips of the branches. All of us, from mammals and birds to fish, descend from shared ancestors who lived about four hundred million years ago. It seems that these distant ancestors already had the capacity for some of the basic emotions, such as fear, as well as the ability to feel pain.

French grunts forage for food

In the near future, we can expect to find out a great deal more information about the experiences and cognitive capacities of fish, as they are the one group of vertebrates cognitive researchers have only really begun to focus on during this century.

One of the biggest surprises for researchers has been to discover how much of the behaviour of wild fish is based on what the individual has learned during its lifetime. Some species combine this with the ability to learn from the examples of others, not just through individual experience. Learning capacity among wild fish has been studied at sites such as coral reefs, where good visibility makes research logistics easier.

One of the studied species is the French grunt, a yellow- and silver-streaked schooling fish. The preferred food for this species can usually be found far away from its resting sites on the reef, so the fish move in schools from their nesting sites to the feeding areas and back every day.

Sometimes young, inexperienced individuals join the school and learn the route by swimming with the others. Researchers have moved marked young individuals from one resting site to another and tracked their movements to ensure that they are in fact learning the route and not just following others.

Flapping is not just a reflex

One of the most studied cognitive processes in fish is their ability to feel pain. Even though a vast majority of fishing enthusiasts may genuinely believe that a fish flapping on a hook, in a net or on the bottom of a boat is just manifesting unconscious reflexes, brain and behavioural studies unfortunately indicate otherwise.

In learning experiments, fish have exhibited a strong tendency to avoid places and situations in which they have previously felt pain. The chemical reactions in the brains of fish during a painful experience are similar to those in mammalian brains. In an experiment in which a fish is subjected to persistent pain which it cannot relieve itself, the fish will in some cases resort to self-rocking, similar to what has been observed in mammals in an equivalent situation. Such a meaningless, repetitive movement causes the release of small amounts of endorphins, the body’s own opioids, which have a slight pain-relieving effect.

If the fish is given morphine, it will stop displaying pain-related behaviour. These things are difficult to explain in any other way than by concluding that the fish is experiencing pain.

New stunning methods?

As the body of research on the topic increases, more information is also  gradually making its way to the general public. For example, Victoria Braithwaite, an American professor of ichthyology, has written a book Do Fish Feel Pain? which is a popularised compilation of balanced information based on research.

New information means the potential for new applications. For example, fishing professionals and researchers could cooperate in the future to find new ways of stunning fish. Fish which suffocate on the deck of a boat die slowly, and they feel pain as their gills dry. Fish farming and the evaluation of the related environmental effects is another potential area of cooperation between the scientific community and other sectors of society.

This essay was published in Finnish in the Y/09/16 issue of Yliopisto magazine.

Helena Telkänranta is evolutionary biologist and award-winning author from University of Helsinki. In 2017 Telkänranta will be working in University of Bristol.