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
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?
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.
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
do you conclude from this? Are the fish aware of themselves?
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
any case, the test demonstrates that the fish are extremely adaptive
and can exploit new opportunities for themselves.
can the mirror test then tell us in the first place?
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 colors. It
is important to remember that other highly evolved animals, such as
dogs or cats, do not pass the test either.
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.
can you find out what other organisms think, feel, perceive?
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
could we nevertheless get an idea of what is going on inside a fish?
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
are commonly regarded as primitive and not very intelligent. Is this
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.
fish are not dumber or worse than us, they are just different!
smart are fish?
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.
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.
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.
can fish do?
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.
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.
not only that: some species can also distinguish conspecifics
individually. Damselfish, for example, have individual color markings on their faces that are only visible in ultraviolet light,
which they use to recognize each other.
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
do these findings mean for how we treat fish today?
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
you for this interview!
by Harald Rösch
Source / Credit: MAX-PLANCK-GESELLSCHAFT