Animal Oh, it's you! Fish can tell people apart
Divers don't all look the same to fish. If they get food from a person, they recognize them and follow them persistently, as a research team from the Max Planck Institute of Animal Behavior (MPIAB) in Constance reports.
19.02.2025, 01:29
SDA
Less generous divers, on the other hand, are ignored. However, it is not the faces - which can barely be seen under the diving mask - that are decisive for recognition, but the characteristics of the equipment.
Researchers at the Mediterranean station "Stareso" in Corsica noticed that sea bream and other fish followed them on dives and snatched food that was actually intended as an experimental reward. They were astonished to discover that only the humans from whom the fish had previously received treats were being followed, as the Max Planck Institute explains.
Curious fish as voluntary test participants
A team led by MPIAB researchers Katinka Soller and Maëlan Tomasek then started a series of experiments with fish that were used to humans in the vicinity of the research station. The animals took part in the experiments as volunteers who could come and go as they pleased.
Soller, as the training diver, initially tried to attract the attention of the fish: Wearing a bright red vest, she fed animals that swam up to her, diving about 50 meters. Gradually, all conspicuous features such as the vest were removed. Finally, Soller, wearing simple diving gear with hidden food, only covered the full 50 meters until she fed the fish that had followed her so far.
Sea bream are real smarties
After twelve days of training, around 20 fish followed Soller on her dives. Sea bream were particularly curious and willing to learn. "As soon as I entered the water, it only took seconds before I saw them swimming towards me, seemingly out of nowhere," said Soller.
The experiments presented in the journal "Biology Letters" also showed what exactly the fish recognize: not the face of the humans, but colour characteristics of their equipment. Tomasek initially used equipment that differed from Soller's equipment only by a few colored parts of the wetsuit and different colored fins. If he also dived but did not feed the fish, he was largely ignored from then on. With completely identical diving equipment, the fish were unable to tell the difference.
Even a goldfish knows how to choose
Anyone who owns an aquarium or pond will be familiar with the phenomenon of their own fish swimming towards them, but not strangers, as Matthias Wiesensee, Vice President of the German Aquarium and Terrarium Association, said. In addition to visually recognizable patterns, sound characteristics such as the voice or gait play a role, which are detected by the animals' lateral line organ.
This is very pronounced in koi and goldfish, for example, which flock to those who feed them - but not to other family members, according to Wiesensee. Large cichlids such as angelfish and discus also noticeably build up a relationship with certain people and are often rather skeptical of strangers.
Overall, however, there is little scientific evidence to date that fish can actually recognize humans, the institute continued. Captive-bred archerfish have been able to recognize images of human faces in laboratory experiments. "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," said Tomasek.
There may be much more to the relationship
With more time, the fish may eventually 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 scrutinize our bodies," says Soller. "It was as if they were studying us and not the other way around."
Incidentally, the recognition in the Constance researchers' experiments was based on reciprocity: one fish was named Julius by the team, while a regularly participating sea bream with two shiny silver scales on its back was given the name Bernie. And then there was "Alfie, who had a tear in his tail fin", as Soller recounted.
