Fish Recognize Divers Based on Equipment Cues, Not Faces
Abstract:
Divers donning different gear sets evoke distinct responses in fish, with those who provide sustenance garnering consistent attention. This recognition stems not from facial features, but rather from specific equipment characteristics, as demonstrated in a series of experiments conducted by researchers at the Max Planck Institute for Behavioral Biology.
Introduction:
Contrary to popular belief, divers exhibit distinct appearances to fish. Those who offer sustenance elicit recognition and persistent companionship, while less generous counterparts are met with indifference. This intriguing observation sparked an investigation into the recognition mechanisms employed by fish, with surprising results.
Methods:
At the Mediterranean research station "Stareso" in Corsica, researchers witnessed fish following divers and pilfering food intended as experimental rewards. Intriguingly, only individuals who had previously received treats from these divers exhibited such behavior.
To delve deeper, a team led by MPIAB researchers Katinka Soller and Maëlan Tomasek designed experiments involving human-habituated fish near the research station. The fish participated voluntarily, with the freedom to come and go as they pleased.
Experiments:
Soller, designated as the training diver, initially donned a conspicuous red vest while feeding approaching fish. As the experiment progressed, these conspicuous features were gradually eliminated. Ultimately, Soller traveled the full 50 meters in standard diving gear, concealing food, before feeding the fish that had followed her.
Results:
After twelve days of training, approximately 20 fish consistently accompanied Soller on her dives. Sea breams displayed notable curiosity and learning abilities. "The moment I entered the water, it only took seconds before I saw them swimming towards me, seemingly out of nowhere," remarked Soller.
The experiments, published in the journal Biology Letters, revealed a crucial aspect of fish recognition: equipment cues, rather than human faces. Tomasek employed gear that differed from Soller’s only in colored sections of the wetsuit and differently colored fins. When Tomasek dived but refrained from feeding the fish, they largely ignored him. However, with identical diving attire, the fish could not distinguish between the divers.
Discussion:
Aquarium and pond owners have long observed similar phenomena. Fish eagerly approach those who provide nourishment, but remain apathetic towards strangers. Besides visual cues, auditory signals, such as voices or footsteps, perceived through the fish’s lateral line organ, also play a role.
This is particularly evident in koi and goldfish, which readily approach their feeders but not other family members. Large cichlids, such as angelfish and discus, also forge noticeable bonds with specific individuals, often displaying skepticism towards unfamiliar faces.
Scientific evidence for fish recognizing humans has been scarce. Captive archerfish have demonstrated the ability to recognize human faces in laboratory experiments. "But no one had ever asked whether wild fish possess the ability or even the motivation to recognize us as we enter their underwater world," said Tomasek.
With extended exposure, fish may eventually become adept at recognizing more subtle cues, such as hair or hands. "We have already observed them approaching our faces closely and scrutinizing our bodies," Soller noted. "It was as if they were studying us, not the other way around."
Interdependence and Recognition:
The recognition in these experiments was a reciprocal process. One fish was affectionately named Julius, while a frequent sea bream with two silvery scales on its back was dubbed Bernie. Another participant, sporting a torn tail fin, became known as "Alfie."
Conclusion:
Fish are capable of recognizing individual divers based on distinctive equipment cues, forging relationships based on sustenance. This ability highlights the fishes’ remarkable cognitive abilities and underscores the importance of responsible diving practices.
