You have probably heard that fish have a three second memory or that they are unable to feel pain. Neither of these statements is true, but it is telling that these misconceptions do not apply to other vertebrates.
Maybe it’s because fish seem so different from us. They don’t seem to have any capacity for facial expression or vocal communication, and we don’t even breathe the same air. Together, these differences separate them so much from humans that it is difficult for us to relate to them.
However, when scientists have conducted experiments to learn more about fish, including their neurobiology, social life, and mental faculties, they have discovered time and again that they are more complex than is often believed. In fact, they seem to have more in common with us than we would like to admit.
In my research I often work with the zebrafish, the aquatic laboratory rat. Here are five fascinating things that other researchers and I have discovered about them.
1. Fish lose their memory as they age
As human beings age, our memory declines. Scientists are working to understand the biology of cognitive decline in order to predict how we can help people age better and develop treatments for conditions such as Alzheimer’s disease and dementia.
In humans, working memory, the mental process we use to perform daily tasks, declines as we age. My colleagues and I found something similar when we observed zebrafish at six and 24 months of age swimming in a Y-shaped maze.
We found that older fish had a harder time navigating the maze compared to younger ones. What’s more, when we designed a virtual version of the task for humans, we found that 70-year-olds showed exactly the same deficits as fish.
2. They like the same drugs as humans
Biologists Tristan Darland and John Dowling of Harvard University (USA) found that zebrafish especially like cocaine. They confirmed this by placing the drug in their tank when the fish circled following a certain visual pattern. This preference is also hereditary. Offspring of fish with a predilection for the drug passed it on to their offspring, a pattern reported in humans.
Zebrafish also display the compulsive drug seeking patterns seen in addicted people. Caroline Brennan’s research group at Queen Mary University of London (UK) found that fish agreed to be caught with a net if it meant access to cocaine.
Working with the Brennan and Pfizer group, we tested other drugs (opiates, stimulants, alcohol, and nicotine) to find out what the zebrafish was telling us about their potential use of other drugs. Turns out they liked all of them… except THC, the main psychoactive ingredient in cannabis.
3. Fish remember their friends
You probably already know that fish are social animals. They can synchronize their behavior in the schools (of fish) so that each individual reflects the movements of its neighbor and the group appears to move as one.
What you probably don’t know is that each fish can recognize other fish in its own group (by smell, usually). Young prefer their own relatives, but as adult females age, they prefer known females and unknown males. This helps prevent inbreeding.
Fish retain these memories for 24 hours and prefer to get close to a new fish rather than the last one they hung out with. This shows that his social memories are strong and turns the gossip that his memory only lasts three seconds into a fad.
4. Fish feel pain
They really do. In 2003, biologists Victoria Braithwaite and Lynne Sneddon, then at the University of Edinburgh and the Roslin Institute, put acid on the lips of trout. The fish showed classic pain responses: move away, rub their lips on the bottom of the tank, increase their breathing. This behavior disappeared completely once they received a pain reliever.
However, the question remains how fish experience pain. What does pain mean to the animal? It is not just the perception of a physical event, such as stubbing your toe. It is often an emotional experience as well. Some researchers think that fish do not experience pain this way.
They argue that, although they feel pain, they are not mentally capable of having an emotional response to that pain, so their suffering should worry us less. This is because, according to them, fish lack the parts of the brain that in humans and other higher vertebrates are associated with the mental experience of pain.
But that argument is no longer so convincing. Decades of work show that all kinds of brain shapes, sizes and organizations exist in nature, and that many complex behaviors arise in animals that lack the brain structures that have been linked, in humans and other primates, to these higher processes.
In fact, it seems that the brain structures themselves may be less important than we think. Therefore, fish could have a more sophisticated experience of the world than we imagine, although using a brain that is quite different from ours.
5. Fish can get impatient
In my lab we are interested in something called impulse control. It is the ability of someone to plan their behavior and wait for the best moment to do it. Poor impulse control is a trait seen in people with various psychiatric conditions, including attention deficit hyperactivity disorder, addiction, and obsessive compulsive disorder.
We trained the zebrafish for several weeks in a series of tests, using a specially designed tank. In each test, the fish had to wait for a light to come on at the opposite end of the tank before they could swim through a pipeline to get food. If they reacted by swimming immediately, they were disappointed because there was still no food and they had to start over. We saw a great variation in their ability or desire to wait. Some fish were very impatient, while others did not mind waiting. We even found that a drug used to treat ADHD also makes fish less impatient.
Maybe the next time you see a fish you will think twice about treating it like a water automaton, only fit to be eaten with tartar sauce and pea puree.