Wild Fish Can Recognize Individual Human Divers

A fascinating new study published February 19, 2025, in the Royal Society’s Biology Letters reveals that wild fish can recognize and discriminate between individual human divers. Researchers Maëlan Tomasek, Katinka Soller, and Alex Jordan conducted experiments with two species of sea bream in the Mediterranean Sea and discovered that these fish can learn to identify specific divers – but only when they’re wearing distinctive gear.

Following for Food

The study centered on a simple but elegant premise: can wild fish tell human divers apart? While many pet owners swear their goldfish recognize them, scientific evidence for this ability in wild aquatic animals has been scarce until now.

The research team trained two fish species – saddled sea bream (Oblada melanura) and black sea bream (Spondyliosoma cantharus) – to follow a human diver who would reward them with food. Then came the crucial test: would the fish discriminate between two different divers and consistently follow the one offering rewards?

The results were remarkable. When the two divers wore different gear (different colored wetsuits, fins, and masks), both fish species quickly learned to identify and follow the “correct” diver who provided food rewards. Some individual fish, which the researchers could identify by unique markings, showed particularly strong learning curves.

However, when the divers switched to identical diving equipment, the fish’s ability to discriminate between them almost completely disappeared. This strongly suggests the fish were using visual cues from the diving gear, rather than recognizing the divers themselves.

Not Just Another Human Face

As someone who’s studied animal cognition for years, I find these results particularly intriguing. We often underestimate the perceptual and cognitive abilities of fish, yet here we see wild sea bream rapidly learning to distinguish between human divers – creatures they would rarely encounter in their evolutionary history.

What’s especially noteworthy is that these fish weren’t specially bred or domesticated. The researchers deliberately chose to study wild fish to avoid the confounding effects of selective breeding or prior experience with humans. This suggests that the fish are using pre-existing cognitive abilities – likely evolved for other purposes like recognizing prey, predators, or conspecifics – and applying them to a novel situation.

The finding that fish relied primarily on diving gear for recognition also makes perfect sense. As the researchers note, sea bream are tetrachromatic with excellent color vision. Underwater, where diving masks obscure human faces and distort appearances, the distinctive colors and shapes of diving equipment would provide much more reliable visual cues than the small portions of human faces or bodies that remain visible.

Implications Beyond the Reef

This study has several fascinating implications. First, it adds scientific weight to the numerous anecdotal accounts of individual fish recognizing specific human divers or aquarium keepers. It suggests the possibility of genuine bonds forming between humans and fish – a concept that might seem strange but is increasingly supported by evidence.

For researchers, it demonstrates that cognitive studies with wild fish are feasible, as these animals will voluntarily and repeatedly interact with specific human divers. This opens new methodological avenues for studying fish cognition in natural environments rather than laboratory settings.

There are practical implications too. As the authors humorously note, “Researchers might not always want to be followed all around by fish, but if they do, they will not be disappointed.” Indeed, scientists conducting underwater observations might need to account for the possibility that their presence could attract or repel certain fish based on previous interactions.

Not So Different After All

What strikes me most about this study is how it narrows the perceived gap between fish and more “advanced” vertebrates. We readily accept that dogs, cats, horses, and even some birds can recognize individual humans. Yet we’ve been reluctant to extend this ability to fish, perhaps due to our tendency to view them as “primitive” or lacking in cognitive sophistication.

This research joins a growing body of evidence that fish possess more complex cognitive abilities than we’ve traditionally given them credit for. They can use tools, recognize themselves in mirrors, remember complex spatial layouts, and now, it seems, distinguish between individual humans.

The next time you peer into an aquarium or don your diving gear, remember – those fish might very well be recognizing you too. Just make sure you’re wearing something distinctive if you want them to remember you on your next visit.