Can fish recognize humans? Yes, but under one condition…

German scientists set out to investigate whether and under what circumstances wild fish can recognize humans underwater. The results of their experiment are quite surprising and shed new light on the cognitive abilities of fish as well as the potential for developing their relationship with humans.

The experiment with divers

The study was conducted in July 2024 at a research facility located in Corsica, on the shores of the Mediterranean Sea. Two species of fish from the sea bream family voluntarily participated in the experiment: saddled seabream (Oblada melanura) and black seabream (Spondyliosoma cantharus). The voluntary nature of the experiment was due to the open-water context—fish could freely swim in and out at any time.

The first phase of the study involved training. For 12 consecutive days, divers descended to depths of 4-8 meters and trained fish that spontaneously approached them to follow them, using bait as an incentive. The diving guide provided the fish with multiple distinctive stimuli, including the smell of an open food pouch, a colorful vest, and a specific set of movements. Over time, the fish learned to swim after the diver even when these stimuli were reduced and the food reward was no longer given.

In the second part of the experiment, two divers with similar physiques but wearing wetsuits and fins in different colors entered the water. Only one of them—the same one each time—fed the fish that followed him. The experiment revealed that the fish quickly learned to recognize the diver who provided food. However, this ability disappeared when both divers wore identical suits, despite noticeable differences in gender, hair length, and hair color.

How do fish recognize humans?

Both saddled seabream and black seabream quickly learned to distinguish which diver carried the promise of food. The experiment demonstrated that fish recognize humans solely based on visual cues. However, their senses are not sharp enough to notice when a person changes their outfit. Clothing, particularly its color, seems to play a crucial role. To be fair to the fish, it’s worth noting that a diving mask on the face does not make identification any easier.

Colors play a key role in the perception of these fish, as saddled seabream and black seabream possess tetrachromatic vision, meaning their retinas contain four types of cones responsible for detecting different wavelengths of light. As a result, their range of perceived colors significantly exceeds human visual capabilities. In the underwater environment, this provides a major advantage, allowing them to better recognize predators, food, and important elements of their surroundings for survival.

Why does this matter?

One might wonder what significance the fact that fish recognize humans based on their clothing has. At first glance—not much. However, the study’s authors highlight its broader scientific context.

Wild fish live in an environment where encounters with humans are rare, making it unlikely that they have evolved an ability to assess people based on their attire.

A more plausible explanation is that fish recognize humans due to innate cognitive abilities that have nothing to do with the human species. How does this translate into the potential for building relationships between humans and schools of black seabream? The experiment proved that, despite not being domesticated, fish are quite willing to engage in interactions and learn surprisingly quickly.

The researchers suggest that it would be valuable to deepen our understanding of the cognitive potential of underwater species, which we often dismiss by saying they have no voice. Especially since fish from the cichlid family, for instance, have been shown to remarkably distinguish subtle differences in facial color patterns within their own species.

It may turn out that fish, though silent, will continue to surprise us in ways we never expected.

main photo: Sebastian Pena Lambarri / Unsplash