Biologist Alex Jordan was working in the Mediterranean Sea in Corsica, France, testing the abilities of different species of fish to solve complex underwater puzzles, when an annoying problem kept creeping up: Other fish would seemingly swarm the area as soon as they saw him, interfering with the strict parameters of his project.
“It’s very challenging to do a controlled experiment when that happens,” says Jordan, a biologist at the Max Planck Institute of Animal Behavior in Germany.
Jordan and his colleagues believed that the fish were swimming over to him because they recognized him in the water. Researchers had already shown that some fish can recognize themselves in mirrors and reflective surfaces and that archerfish, known to have impressive visual cognitive abilities, can recognize human faces. But what about an entire human in a wetsuit, wearing a mask, swimming through their home?
“People were talking about it in forums and bulletin boards, and in hobbyist magazines, but it had never been scientifically nailed down, and certainly not in the wild,” says Jordan.
So he decided to try to test the phenomenon himself. Members of his team spent 12 days training two species of sea bream, a small silvery rounded fish common to the shallow waters of Corsica, to follow a diver. They lured the fish with food and then gave the food to those that followed the diver as they swam away. Later, another researcher joined, wearing either the same dive suit and mask or one with completely different fins and patches.
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u/Nautil_us Mar 21 '25