"Fish are not stupid, they're just different!"

Alex Jordan is a behavioral ecologist at the Max Planck Institute of Animal Behavior in Konstanz, Germany. His main interest: he wants to know why animals do what they do. He is especially devoted to fish, having been a hobbyist since a young age, and seeing the value of being able to study animals equally well in the wild as in captivity.
 

Alex, a few years ago you conducted a study that resonated strongly in the scientific community on the reaction of cleaner wrasses to their mirror image. What did you find out in the process?

We placed marks on the cleaner wrasses' bodies that they could only see in a mirror. The fish then tried to remove these marks. We performed various tests to make sure that the fish only reacted to marks that they saw on their own bodies in the mirror an nothing else.

A mirror test passed in this way is considered by researchers to be evidence of self-awareness. Only a few species score positively in this test, for example apes, corvids, dolphins - and now cleaner wrasses.

What do you conclude from this? Are the fish aware of themselves?

No, I don't think so. I suspect the wrasses have simply learned that a mirror creates an image of something - in this case, themselves. Since dark spots on fish bodies are an important signal for wrasses by nature - they usually represent parasites, which the wrasses feed on - they are naturally particularly interested in this. However, they probably do not possess self-awareness or even self-consciousness.

In any case, the test demonstrates that the fish are extremely adaptive and can exploit new opportunities for themselves. 

What can the mirror test then tell us in the first place?

In my opinion, the mirror test is not well suited for studying self-awareness in animals. We also did the test with African cichlids from Lake Tanganyika. They didn't care about the marks on their bodies at all. Also the cleaner wrasses passed the test only if the marks were brown. They didn’t care about marks of other colours. It is important to remember that other highly evolved animals, such as dogs or cats, do not pass the test either.

There are different reasons why an animal does not react to the marks, so in my opinion the test is not suitable to answer the question about self-awareness. It was developed by humans for humans. For most animals, it just doesn't fit.

How can you find out what other organisms think, feel, perceive?

That is very difficult in principle. Even you and I differ in how we perceive things. But you can at least describe your cognitive status to me. Since we can hardly or not at all communicate with animals, we can only infer what they feel, want, think. Some degree of uncertainty will always remain, because we can't help but take ourselves as the measure of all things. To leave our human world of experience and to put ourselves into the world of a fish is all but easy.

How could we nevertheless get an idea of what is going on inside a fish?

We want to try this with a completely new approach. We will measure the activity of nerve cells in the brain when zebrafish react to conspecifics or when they face their mirror image. If there are different activation patterns in the brain in the two cases, this would indicate that the fish are not seeing a conspecific, but themselves. That would be a strong hint for the fish being self-aware.

Fish are commonly regarded as primitive and not very intelligent. Is this justified?

Not at all. We need to stop seeing ourselves as the pinnacle of evolution and ranking other animals in descending order below. All organisms on earth are the result of millions of years of evolution. They and their predecessors have always managed to defy all odds and adapt. Seen in this light, even a bacterium is highly evolved.

Consequently, fish are not dumber or worse than us, they are just different!

How smart are fish?

We don't know exactly yet, but there are definitely differences between species. Fish that migrate in large anonymous schools through the ocean probably need less higher mental abilities than those that defend territories, for example. So I would expect more from a Tanganyika cichlid than from a mackerel.

It is known from other groups of animals that species with a narrow food spectrum are less capable cognitively than those that eat a variety of foods. Thus, the omnivores among fishes might generally be "smarter" than specialists.

Marine fish often exhibit more complex behaviors than freshwater species - simply because inland waters have not existed as long as the oceans, and therefore they have less time to develop such behaviors.

What can fish do?

Some fish are very sophisticated. They can play and use tools, they predict the actions of others, and they even cheat and reconciliate. Some species thus possess higher cognitive abilities than other vertebrates. They may not be that far from apes and humans.

Fish can also recognize people. They know who to expect food from and who not to expect it from, as many aquarium owners can attest. In our research area in Lake Tanganyika, for example, predatory fish from the genus Lepidiolamprologus have learned that they can prey  when my colleague and I are out diving. In doing so, they don't follow me, but her, because she flushes out most of the fish.

And not only that: some species can also distinguish conspecifics individually. Damselfish, for example, have individual colour markings on their faces that are only visible in ultraviolet light, which they use to recognize each other.

Another fascinating example, which we plan to investigate ourselves, is how mullet and wrasses work together in the Mediterranean. When a mullet is foraging and scavenging on the sand, it is often accompanied by a wrasse, which preys on small critters scared up by the mullet. This alone would be nothing special, but the wrasse keeps touching the mullet - it literally caresses it. Probably the mullet knows in this way that there is no danger from above while it burrows underground. The "masseur" thus ensures that the mullet stays in its territory.

What do these findings mean for how we treat fish today?

Even if there is still a lot we don't know, one thing is clear: fish can do more than we have given them credit for up to now. They are sentient animals capable of cognitive engagement with the world around them, including social interactions, fear, suffering, and enjoyment.

Thank you for this interview!

Interview by Harald Rösch