At a research station in the Mediterranean Sea, a team of scientific divers noticed that some groups of local fish called seabream would follow them around every field season. They even stole food the divers carried that was meant to be used as rewards for other fish in their experiments.
The seabream appeared to be able to recognize the divers, and the team suspected that they even knew which individual humans had previously carried the food because the fish were not thrown off by decoy divers. They continued following specific divers and ignoring others.
So, the team designed a series of tests to see just how well the seabream can tell humans apart. In the first experiment, one of the researchers spent 12 days training wild saddled seabream and black seabream to follow her around.
She donned a bright red vest and fed the fish as she swam for about 164 feet. Then, she gradually transitioned to wearing more plain diving gear. She also only fed the seabream that trailed her for the entire distance.
“Once I entered the water, it was a matter of seconds before I would see them swimming toward me, seemingly coming out of nowhere,” said Katinka Soller, a co-lead author of the study from the Max Planck Institute of Animal Behavior.
“There was Bernie with two shiny silver scales on the back and Alfie who had a nip out of the tail fin.”
For the second phase of the experiment, the team wanted to see if the seabream recognized Soller. Another researcher from the Max Planck Institute, Maëlan Tomasek, joined her in the water, wearing differently colored diving gear. They both started at the same point in the water and then swam off in opposite directions.
On the first day, the fish followed both of them equally. Tomasek never fed the fish that followed him. From the second day, more of the fish began to follow Soller.
The team focused on six fish to study individually to confirm that they were actually learning to recognize each diver. Four of the six became better at choosing which diver to follow over time.
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“This is a cool result because it shows that fish were not simply following Katinka out of habit or because other fish were there,” said Tomasek.
“They were conscious of both divers, testing each one and learning that Katinka produced the reward at the end of the swim.”
However, when they repeated the experiments wearing identical gear, the fish appeared to be unable to tell them apart.
The findings indicate that the fish were differentiating between the divers according to the colors of their gear.
Humans have a tendency to underestimate the intelligence of fish. This study shows that fish are smarter than we think.
The results of the study were published in the journal Biology Letters.
