Do fish recognize people? Yes, but on one condition…

German scientists decided to study whether and under what circumstances wild fish recognize humans who are underwater. The results of their experiment are quite surprising and shed new light on the level of cognitive abilities in fish and the possible prospects for their relationship with humans.

Experiment with divers

The study was conducted in July 2024 at a scientific site located in Corsica, on the shores of the Mediterranean Sea. Two species of fish belonging to the prairie fish family took part in the experiment voluntarily: obladas(Oblada melanura) andcantharus (Spondyliosoma cantharus). The voluntariness of the experiment was due to the context of open water – the fish could swim in and out on their own at any time.

The first part of the study involved training. For 12 days in a row, divers dived to depths of 4-8 meters and taught the fish, which spontaneously swam up, to follow them using a lure. The diving guide provided the fish with a number of characteristic stimuli including the smell of an open bag of food, a colorful vest or a set of characteristic movements. Gradually, the fish learned to swim in the diver’s footsteps, even when the stimuli were reduced and the reward was discontinued.

In the second part of the experiment, two divers with similar physiques, but wearing different suits and fins of different colors, went underwater. Only one of them – always the same one – served food to the fish that followed him. The experiment showed that the fish quickly learned to recognize the diver who was feeding them. However, this ability disappeared when both divers wore identical outfits, despite apparent differences in sex, length and hair color.

Fish recognize people by…

Both oblates and canids learned quite quickly to distinguish who was carrying the promise of a treat. The experiment shows that fish recognize people based solely on visual stimuli. However, their senses are not sensitive enough to realize that a person has changed clothes. The outfit, especially its color scheme, seems to be of crucial importance. As an excuse for the fish, it is worth adding that a face mask does not make identification any easier.

Colors play a key role in the perception of these fish because oblates and cantharians) have tetrachromatic vision, meaning that their retina contains four types of cones responsible for receiving different wavelengths of light. As a result, the range of colors they see significantly exceeds human perceptual capabilities. In underwater environments, this is a tremendous advantage, enabling them to better identify predators, food and elements of the environment important for survival.

What does it matter?

One may wonder what is the significance of the fact that fish recognize people based on costume. At first glance – little, but the authors of the study point to its broader scientific context.

Wild fish function in an environment where contact with humans is incidental, making it impossible for them to have evolutionarily developed the ability to judge humans based on their clothing.

It seems more likely that fish recognize humans due to innate abilities that have nothing to do with the human race. How does this translate into the possibility of establishing a relationship between a human and a school of canids? The experiment proved that despite their lack of tameness, the fish engage in interactions quite readily and learn surprisingly quickly.

The study’s authors suggest that it would be worthwhile to deepen our understanding of the cognitive potential of underwater species that we are used to rather disdainfully say have no voice. All the more so because fish belonging to cichlids turn out to be surprisingly good at distinguishing subtle differences in color patterns on the faces of individuals of their own species. It may turn out that the fish, though so quiet, will still surprise us more than once.

pic. main: Sebastian Pena Lambarri / Unsplash