Wild fish can tell humans apart! One study found that snappers can recognize individual divers and will follow the diver who feeds them while ignoring others. For years, scientific divers at a research station in the Mediterranean discovered a strange problem - local fish would follow them and eat the food used for their experiments. What's even more interesting is that these fish seem to be able to identify and target specific divers who have fed them, while being blind to other divers.
To test whether wild fish can actually differentiate between human individuals, researchers at the Max Planck Institute for Animal Behavior (MPI-AB) in Germany conducted a series of experiments. By varying their diving gear, they found that wild fish can indeed tell humans apart through visual cues.
Scientists set out to answer a question that had never been tested on wild fish: Can they tell people apart? Although some studies have shown that certain captive-bred fish, such as swordfish, are able to recognize human faces in controlled laboratory settings, there is little evidence that wild fish can do the same.
"But no one has ever asked whether wild fish have the ability or motivation to recognize us when we enter their underwater world," explains Maëlan Tomasek, a doctoral student at the Institute of Fisheries Research in Paris and the University of Clermont-Auvergne in France.
Now, researchers at MPI-AB have put this question to the test - and fish have a clear answer. Wild fish do recognize individual humans. Even more amazing is that they can remember and follow specific divers who have fed them in the past. The discovery was published today (February 18) in Biology Letters.
The team conducted the study eight meters underwater at a research site in the Mediterranean, where wild fish populations have become accustomed to the scientists' presence. Their experiments were conducted in open water, and the fish participated as "willing volunteers" who could come and go as they pleased," explains Katinka Soller, an undergraduate student at MPI-AB who is co-first author of the study with Tomasek.
The first experimental phase—training—tested whether the fish could learn to follow a single diver. Training diver Soller initially tried to attract the attention of local fish; wearing a bright red vest, she fed the fish as she swam a distance of 50 meters. Over time, Soller gradually removed those conspicuous cues until she put on regular diving gear, hid the food, and waited until the fish followed her for 50 meters before feeding.
Of the dozens of fish species that inhabit the marine station, two species of snapper are particularly willing to take part in training sessions. The snappers we are most familiar with are bought to eat, but their curiosity and willingness to learn have surprised scientists.
"Once I'm in the water, it only takes a few seconds for me to see them swimming towards me, seemingly out of nowhere," said Soler. "Not only did the fish learn to follow her, but the same fish came to the course every day. Soler even gave them names: "Bernie had two shiny silver scales on his back, and Alfie had a bite mark on his tail fin." "
After 12 days of training, about 20 fish were reliably following Soller as they trained to swim, and she could identify several of them based on their physical features. By identifying the individual fish involved in the experiment, preparations were made for the next phase of the experiment: testing whether the fish could distinguish Soller from another diver.
This time, Soler dived with Tomasek, whose diving gear was slightly different from hers, especially some of the colored parts of the wetsuit and fins. Two divers start from the same spot and swim in different directions. On the first day, the fish also followed two divers. "You can see them struggling to decide who to chase," Soler said.
But Tomasek never fed the fish that followed him, so starting from the next day, the number of fish that followed Soller increased significantly. To confirm that the fish were learning to identify the correct diver, the researchers selected six fish from a large group and studied them individually and found that four of the fish showed strong positive learning curves during the experiment. "This is a cool result because it shows that the fish are not just following out of habit or because other fish are there. They are aware of both types of divers, tested each type, and learned that the catinka produces a reward when it swims to the end," Tomasek said.
But when Soler and Tomasek repeated the experiment wearing the same diving gear, the fish couldn't tell them apart. Scientists believe this is strong evidence that fish have associated differences in diving equipment, likely color, with each diver. "Almost all fish have color vision, so it's not surprising that sea breams learn to associate the correct diver with color patches on their body," Tomasek said.
"Underwater, the same goes for us," Soler said. "Diving masks distort faces, so we often rely on differences in wetsuits, fins or other parts of our gear to identify each other." Over time, fish may have learned to notice subtler human features, such as hair or hands, to distinguish divers, the authors said. "We've observed them getting close to our faces and looking closely at our bodies," Soler added. "It's like they're studying us, not the other way around."
This study confirms many anecdotal reports of animals, including fish, recognizing humans; but it goes a step further, conducting dedicated experiments in a completely natural environment. Scientists have found that wild fish can quickly learn to use specific cues to identify individual humans, and as a result, many other fish species, including our pets, can also recognize specific patterns to identify us. This mechanism underlies specialized interactions between individuals, even across species.
Senior author Alex Jordan, leader of the MPI-AB team, said: "It doesn't shock me that these animals navigate a complex world and interact with countless different species at every moment, but that they can recognize humans based on visual cues. I think what's most surprising is that we should be surprised by their recognition ability. This suggests that we may be underestimating the capabilities of our underwater cousins."
Tomasek added: "It might seem strange that humans would connect with fish, animals that are so far away from us on the evolutionary tree, because we can't intuitively understand the relationship. But if we pay attention, the relationship between humans and animals can span millions of years of evolutionary distance. Now that we know they can see us, it's time for us to see them."
Compiled from /ScitechDaily