20-02-2025
Oh hey, it's you! Fish can recognize humans, research shows
Divers don't all look the same to fish. If they get food from a person, they will recognize them next time and follow them persistently. Less generous divers, on the other hand, tend to be ignored, as evidenced by researchers at the Max Planck Institute for Animal Behavior (MPIAB) in the German city of Constance.
However, it is not the faces – which can hardly be seen under the diving mask – that are crucial for recognition, but rather the peculiarities of the equipment.
Researchers at the Mediterranean station Stareso on Corsica noticed that sea bream and other fish followed them on dives and even stole food that was actually intended as a reward. They were amazed to discover that the fish only followed the people from whom they had previously received treats, as the Max Planck Institute explains.
A team led by MPIAB researchers Katinka Soller and Maëlan Tomasek then started a series of experiments in the area around the research station, where fish - already accustomed to humans - volunteered in the experiments, coming and going as they pleased.
Soller, as the trained diver, first tried to attract the their attention: Wearing a bright red vest, she fed the fish that had swum over and dived about 50 metres.
Gradually, all conspicuous features, such as the vest were removed. Ultimately, Soller dived a full 50 metres in simple diving gear with the food hidden, until she fed the fish that had followed her up to that point.
Sea bream are particularly clever
After 12 days of training, around 20 fish followed Soller on her dives. Sea bream showed particular curiosity and a willingness to learn.
"As soon as I entered the water, it only took seconds for me to see them swimming towards me, seemingly out of nowhere," Soller says.
Described in the journal Biology Letters, the experiments also showed exactly what the fish recognize: not the human face, but colour features of their equipment.
Tomasek initially used equipment that differed from Soller's equipment in the colour of only some parts of the neoprene diving suit and the fins. If he also dived but did not feed the fish, they largely ignored him from then on.
When the diving equipment was completely identical, the fish were unable to distinguish between the divers.
Even a goldfish knows you
Anyone who owns a fish tank or a pond is familiar with the phenomenon of one's own fish swimming towards you, but not strangers, says Matthias Wiesensee from a German aquarium association.
In addition to visually recognisable patterns, sound characteristics such as the voice or gait play a role, which are detected by the lateral line, a sensory organ found in fish.
This is very pronounced in koi carp and goldfish, for example, which swim to those who feed them – but not to other family members, according to Wiesensee. Large cichlids such as scalars and discus also noticeably develop a relationship with certain people and are often rather sceptical of strangers.
Overall, however, there is little scientific evidence showing fish can recognize people, the institute said. In laboratory experiments, captive-bred archerfish were able to recognize images of human faces.
"But no one has ever asked whether wild fish have the ability or even the motivation to recognize us when we enter their underwater world," says Tomasek.
With more time, the fish might also be able to pay attention to more subtle features such as hair or hands, the researchers suspect. "We have already observed that they approach our faces and examine our bodies closely," says Soller. "It was as if they were studying us and not the other way around."
Recognition in the experiments of the Constance researchers was mutual, by the way: one fish was named Julius by the team; another one, a sea bream that regularly participated with two shiny silver scales on its back, was named Bernie. And then there was "Alfie, who had a crack in his tail fin," as Soller recounts.
