Wild fish can recognise different humans, study finds
Scientists discovered that fish were able to remember and follow specific divers based on which ones had previously offered food.
The study’s author, Maëlan Tomasek, pictured with a “volunteer” fish during the experiment. Credit: Maëlan Tomasek
Wild fish are capable of recognizing individual humans, according to the results of a new study into the intellectual capacity of fish.
Scientific divers at a research station in the Mediterranean Sea first had an idea for the study when they realized local fish would follow them and steal food intended for other research.
The scientists discovered that the fish would choose to follow the specific diver who had previously carried food while ignoring the other divers.
As there is little existing scientific evidence to show that fish can recognize humans, the team of researchers wanted to put the theory to the test: can fish tell people apart?
The subsequent study found that not only can wild fish recognize individual humans, but they can follow specific divers they know will reward them.
Published in the journal Biology Letters, these results suggest that fish can have differentiated relationships with specific humans, not unlike a relationship between a human and a pet.
“It doesn’t come a shock to me that these animals, which navigate a complex world and interact with myriad different species every minute, can recognize humans based on visual cues,” says the study’s senior author Alex Jordan, who leads the group at the Max Planck Institute of Animal Behavior (MPI-AB) in Germany which conducted the experiment.
“I suppose the most surprising thing is that we would be surprised they can. It suggests we might underestimate the capacities of our underwater cousins,” added Jordan.
To conduct the study, the team of scientists at MPI-AB sent divers to swim eight meters underwater at a research site in the Mediterranean Sea where populations of wild fish had become accustomed to the presence of scientists.
In the first stage of the experiment, one individual diver tested if fish would follow her to receive food. The diver, Katinka Soller, wore a bright red vest and fed fish while swimming a length of 50 metres. Over time, Soller then adapted the process by wearing plain dive gear, keeping the food hidden, and only feeding fish after they had followed her swimming for 50 meters.
While there were dozens of species of fish swimming around the research station, Soller found that two species of seabream were particularly engaged in the training sessions.
“Once I entered the water, it was a matter of seconds before I would see them swimming towards me, seemingly coming out of nowhere,” says Soller.
Several of the fish that followed her quickly began to appear day after day, and Soller was able to recognise and even name some of the animals. “There was Bernie with two shiny silver scales on the back and Alfie who had a nip out of the tail fin,” she says.
After 12 days of training, Soller was able to accumulate around 20 fish that were reliably following her during each session.
Researchers then introduced a second diver for the second stage of the experiment. Soller was now joined with another diver, who was dressed in different dive gear, and both divers would swim in different directions.
At first, fish followed both divers equally. But only those who followed Soller were rewarded with food.
Over the next days and training sessions, the number of fish following Soller increased significantly. Fish were learning to recognize the correct diver who offered food, and therefore were choosing to follow Soller for the reward at the end of the swim.
The scientists say that the fish had used the differences in the dive gear, most likely the colors, to differentiate and choose from the divers.
“Almost all fish have color vision, so it is not surprising that the sea bream learned to associate the correct diver based on patches of color on the body,” says Maëlan Tomasek, a researcher who was also the second diver.
The findings help expand the ways in which people think about fish and how they understand the world. Sea bream, the species which were most prominent in the study, are mostly known to humans solely as a fish to be eaten at meal times. But this new study is evidence that they have curiosity, a willingness to learn, and a capacity to tell humans apart.
Tomasek hopes the new research can help us collectively rethink how we view and treat fish.
“It might be strange to think about humans sharing a bond with an animal like a fish that sits so far from us on the evolutionary tree, that we don’t intuitively understand,” says Tomasek. “But human-animal relationships can overcome millions of years of evolutionary distance if we bother to pay attention. Now we know that they see us, it’s time for us to see them.”
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