“When I ran my hands over her skin, the edges of her fins quivered like a dog’s leg sometimes does”

While working on this book, I received a video clip from an astonished viewer who couldn’t understand why a fish—in this case, a bright orange lemon cichlid known to many as the friendly Nemo fish—kept coming back to be petted and lifted out of the water by a human, who would happily return it a moment later.

What could motivate a fish to do this? I believe it was simply pleasurable for it. Fish often touch each other for pleasure. Courtship involves two individuals rubbing against each other or nibbling. Cleaner fish try to please their clients and to this end stroke them with their fins – because such gestures strengthen relationships. Moray eels and groupers swim up to familiar divers and let them stroke them or stroke them under the chin.

I conducted an informal survey of fish perceptions, and in addition to the thousand responses from random respondents, I also received eight reports from people who described fish behaviors similar to those described earlier for the cichlid. These included allowing themselves to be touched, petted, and picked up. Journalist Cathy Unruh later wrote to me about a grouper named Larry, the name she gave to a fish that would come up to her and other divers for petting. She believed that Larry was eager to make eye contact and watch the bubbles rising from the scuba masks. He even turned from side to side—like a dog or a pig might—to be petted all over. Today, there are tons of videos on the Internet of fish frolicking with divers, sometimes even cuddling them. And divers pet them the way you pet a house cat. There are new videos appearing all the time in which aquarium fish swim into their owner’s hand to be petted.

Other fish, such as sharks, rays and stingrays, also seem to enjoy being touched. Diver Sean Payne told the story of a young manta ray he encountered off the coast of Florida that swam up to him and began to rub against him, as if to encourage him to play, and eventually squeezed itself between his hands.

As I ran my hands over her skin, the edges of her fins vibrated like a dog’s leg sometimes does when you scratch its belly vigorously.

– Payne recalled. According to Andrea Marshall, founder of the Marine Megafauna Foundation, manta rays are very curious and eager to interact with people. These large anemones, which have the largest brain of any fish, love to be massaged with bubbles. Marshall swims under them and blows air on them from a tank. When he stops, the manta rays swim away, but they come back for a repeat.

A similar story can be heard at the Shedd Aquarium in Chicago, where five bearded sharks live in a 1,500-cubic-meter tank. Two of them like to swim with local divers. “I think they like the feel of the bubbles from the tanks,” says Lisa Watson, who is in charge of the coral reef animals. “When we do maintenance, we feed them bubbles from underneath, and they swim above and get their bellies tickled.”

It is possible that fish can also enjoy other things besides touch, such as eating, playing, or copulating. In addition, there is also a banal sense of comfort. Southern bluefin tuna from Australia can roll around in the water and expose themselves to the sun for hours. It is not entirely clear why they do this. It is possible that they are simply basking in the sun, which allows them to swim faster and react more efficiently to stimuli, and therefore hunt more effectively. I suppose that this experience can also be simply enjoyable, because pleasure is an evolutionary reward for useful behavior.

Sunfish are famous for lying on their sides just below the surface, basking in the sun. Their huge bodies are home to a multitude of parasites (up to forty different species, including giant copepods that grow to several centimeters). Sunfish line up under layers of floating kelp, waiting for the services of cleaner fish working there. The first in line turns on its side to signal its readiness to be treated.

Not every parasite can be removed in this way, so the sunfish turn to specialists for the largest ones. They swim to the surface and allow the seagulls to pull them out of their skin with their powerful beaks. Sometimes they actively invite the birds to look, swimming behind them or between them. Does this justify the conclusion that the sunfish feels relief when it gets rid of what is biting it? Does it mean that the fish understands the cause-and-effect relationship between the bird and the parasite? In my opinion, this is the most likely explanation for such characteristic behavior of a wise old animal that can live for a century and travel thousands of square miles across the open ocean.

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