What a Fish Feels

by Belinda Recio

Evidence indicates that fish may not only be playful, but emotional

In her book, Unlikely Friendships, author Jennifer Holland presents stories about interspecies animal pals. Most of the stories are about mammals, a few involve birds and reptiles, and one features a fish. Falstaff was a koi fish (a large carp commonly found in outdoor water gardens) who had a “friendship” with Chino, a golden retriever. Whenever Chino approached the pond, Falstaff would immediately swim over to meet him. The two friends greeted by touching noses, then Chino would lie at the edge of the pond, peacefully watching Falstaff. During their visits, Falstaff sometimes approached Chino and gently nibbled on his paws.

Out of all the touching stories in Holland’s book, it was Chino and Falstaff’s friendship that most intrigued me. The idea of a fish showing what appeared to be friendly interest in a dog just didn’t match up with how I thought fish behaved. I have always been intrigued by fish—who isn’t fascinated by evolutionary adaptations such as the bioluminescence of deep sea fish or the mobility of the mudskipper, who can walk on land and even climb trees? But I didn’t think of fish as being particularly intelligent, let alone emotional. And then I read What a Fish Knows: The Inner Lives of Our Underwater Cousins by ethologist Jonathan Balcombe and my ideas about fish were forever changed.

Balcombe presents research and anecdotal stories that portray fish as complex, sentient creatures who play, cooperate, fight, reconcile, use tools and engage in other behaviors that most of us associate with more familiar terrestrial animals. I was especially struck by stories about the piscine capacity for pleasure and play. For example, some captive fish have been observed riding air bubbles and batting around aquarium thermometers, presumably just to amuse themselves. Another fish—a cichlid—engaged in social play with another species. He played an ambush game with a cat that liked to steal a drink of water from his tank. The fish would hide until the cat approached the top of the tank and then dart up to the surface to startle the thirsty feline. The two unlikely playmates repeated this game over and over, always without injury.

As for pleasure, Balcombe reports that some pet fish regularly swim into the hands of their humans to be gently held and stroked, and wild fish seek out human touch, too. He recounts one story about an especially friendly grouper that eagerly approached divers to be petted and even rolled to his side to get a good rub, the way dogs do. And when they are among themselves, fish stroke, rub up against, and playfully nip one another in non-aggressive contexts, presumably because it feels good.

Another source of pleasure is companionship. Like other animals, fish seem capable of developing close bonds that may even involve empathy. Balcombe tells the story of Frankie and Zooey, two gold barbs kept in an aquarium. One day during an aquarium cleaning Frankie jumped out of the holding container and injured himself. Zooey immediately started to swim frantically and behave in an agitated manner. After the injury, when Frankie was listless and largely immobile, Zooey tended to him unrelentingly, nudging and pushing him off the bottom of the tank, as if trying to get him moving again. It took Frankie awhile to recover, and Zooey remained visibly agitated until he was back to normal.

It’s easy to imagine that Frankie might have been in pain while he was lying on the bottom of his tank. But the question of whether fish feel pain is subject to ongoing debate in the scientific community. Some scientists assert that even though fish have the sensory receptors associated with pain signals, they do not feel pain. They believe that a fish’s reaction to injury is more like a reflex—an unconscious reaction that looks like pain, but isn’t experienced in the same way that other animals feel pain.

But then there are those scientists, including Balcombe, who believe that there is plenty of evidence that fish do feel pain. To make his case, Balcombe presents several studies, including an experiment that looked at whether fish would seek relief from pain even if it meant paying a price. In this study, zebrafish were placed in a tank with two different chambers. One chamber was barren and the other was enriched with rocks and plants to create a more natural environment with places to explore and hide. Not surprisingly, all of the fish hung out in the enriched chamber. The researchers then divided the fish into two groups, injected one with a harmless saline solution, and the other with acetic acid, which causes pain. After the injections, all of the fish remained in the enriched chamber. But when the researchers dissolved a painkiller in the barren chamber, some of the fish moved into that chamber despite their demonstrated preference for the enriched environment. Can you guess which fish moved into the undesirable barren chamber with the dissolved painkiller in the water?

When discussing the question of sentience—the capacity to feel pain, pleasure, affection, anxiety and more—Balcombe uses pregnancy as an analogy: “You’re either pregnant or you’re not; you’re either sentient or you’re not.” Balcombe’s book, along with recent research, suggest that we need to revisit our assumptions about what fish feel, and start treating them with more respect and compassion.


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