During his first year of graduate school in California, Brad Erisman’s advisor instructed him to watch a group of kelp bass gathered under a dock. Many mundane hours later, he returned and asked Erisman what he had observed. “They’re not doing anything,” he replied. “They’re just sitting there.” “It’s not that they’re not doing anything,” his advisor corrected him. “It’s that you’re not cued in on their behaviors.” He returned to the dock. Thousands of hours of observation later, Erisman—now a fisheries ecologist at the University of Texas—readily recognizes the errors of his early days. There was a whole underwater world of subtle communication, individual behaviors, and group dynamics taking place right in front of his eyes. He just couldn’t see it at the time.

Most of us, however, never learn that lesson. As Erisman says, “People just look at fish as something to be put on a plate.” In fact, science is increasingly revealing that fishes are intelligent, emotional beings—but the inflated value we tend to assign to all things human often prevents us from accepting such findings, says biologist Jonathan Balcombe, author of What a Fish Knows . Because fishes lack faces like ours, we assume that their mask-like features mean they do not experience feelings. And because fish cannot cry out, we interpret their silence as meaning they do not perceive pain—even as their gasping mouths and flopping fins on a ship’s deck indicate otherwise.

Science is increasingly revealing that fishes are intelligent, emotional beings.

“Their bodies are shaped differently, their eyes don’t blink, they’re bathed permanently in water and—while they make lots of sounds underwater—we don’t hear them because they’re transmitted in an aqueous environment,” Balcombe says. “But they are sentient creatures with the capacity to feel.” Humans also tend to assume that because fishes are cold-blooded (put more precisely, ectothermic) and began evolving around 100 million years before land animals, they must be “primitive.” But evolution is anything but static, and fishes’ early start actually means they’re the most highly evolved of all vertebrates, Balcombe points out. Many of the world’s 33,000-plus known species of fish possess incredible senses and abilities, some of which we are only just beginning to understand. “People forget that fish were here long before we were, so they’ve had much more time to specialize and to do funky things that we haven’t even wrapped our heads around,” says Marah Hardt, author of Sex in the Sea and research director for Future of Fish, a non-profit dedicated to solving ocean challenges. “When evolution is given time, she really gets creative.” Indeed, as scientists like Balcombe and Hardt slowly chip away at the mysteries of lives lived under the sea, it’s becoming more and more obvious that we have grossly underestimated our underwater cousins. “There’s so much we’re still learning,” Hardt says, “and what we’re learning is that they’re far more complex than we previously thought.” Tools, Toots, and Treats People tend to assume that fish are little more than aquatic automatons, when in fact many are highly intelligent. For one, some can use tools—something we once assumed was limited to humans and their closest primate relatives. But tuskfishes and wrasses have been observed picking up mollusks in their mouths, carrying them over to specially selected rocks and then self-assuredly bashing those morsels open. Fish are also quick learners, with strong memories. Despite the enduring “three-second memory” myth, even goldfish—which can live up to 40 years—can recall exact colors and locations of specific feeding tubes up to a year after exposure. At some mental tasks, fishes even out-perform primates , including chimpanzees and young children. In 2012, researchers presented two identical helpings of food on a red and blue plate to capuchin monkeys, orangutans, chimpanzees, and cleaner wrasses. The animals could decide which plate to eat from, but after two minutes, the researchers removed the red plate and left the blue one. After 45 trials, all of the cleaner wrasses had learned to eat first from the red plate and then move on to the blue after the red’s removal, maximizing the total amount of food they consumed. All of the orangutans and monkeys, on the other hand, failed to figure this trick out, and just two of four chimps cracked the system—but only after 60 and 70 tries, respectively. Balcombe adds that when one of the study authors tried the same experiment at home with his four-year-old using two plates of M&Ms, she failed to catch on even after 100 trials. Such findings, Balcombe says, are “another reminder of how brain size, body size, presence of fur or scales and evolutionary proximity to humans are wobbly criteria for gauging intelligence.” But even if we do consider brains the ultimate measure of intelligence, some fishes can measure up. Several hundred species of electric fish in South American and Africa have brains that are almost the size of our own, proportionally speaking. “For fish, their brains are just immense,” says Bernd Kramer, a professor of animal behavior at the University of Regensburg in Germany. “That should signal caution to us humans in issuing our judgement.”

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In the electric fishes’ case, their large brain likely evolved to accommodate all the information they receive through electroreception, or a specialized ability to perceive electric stimuli in the microvolt-per-centimeter range. Electric fishes possess three different types of electroreceptor organs: one for detecting predators or prey by tuning into the natural electric fields that all animals give off in water; another for active electrolocation, allowing them to navigate through dark water as a bat does in the night sky; and a third for communicating with each other. The latter receptor is used not only for distinguishing members of their own species from similar ones, but also for identifying themselves and others as individuals. Incredibly, personal identification signals are produced at up to 1,800 pulses per second and differences in signal waveforms can be detected down to one microsecond, Kramer says. Courting males and females synchronize their signals into a type of duet, while competing males take turn issuing their pulses, as though they are arguing. When socializing as a group, individuals will even tweak their frequency by 10–15 Hz from their neighbors, to assure everyone’s electric voice gets heard. “They’re using electric signaling in a way that is unimaginable to us,” Kramer says. “It’s quite amazing—and we don’t know how they do it.” Until recently, it was near scientific heresy to even speculate as to whether fish have emotions. Other species have similarly inventive means to communicate, including by vibrating their swim bladders, grinding their teeth, rubbing their bones together, jiggling their gill covers, and even farting, Balcombe says. Pheromones and visual signals further help fishes convey messages to each other, from signaling danger to broadcasting come-hither invitations for potential mates. All this complex socializing indicates that fish have a sophisticated social lives and depth of feeling—something that evidence has come to support, Balcombe says. But until recently, he continues, it was near scientific heresy to even speculate as to whether fish have emotions. Research findings have changed that. We now know that fish, like mammals, seek out pleasurable experiences and avoid painful ones. Captive aquarium fish ride bubble streams for fun, for example, while wild mobula rays throw themselves up to ten feet into the air for no detectable reason other than they seem to enjoy it. Fish also have social lives not dissimilar to our own, with friends, enemies, and “frenemies,” and they do not limit those bonds to members of their own species.

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For example, cleaner fish, which remove dead skin and parasites from other fish, can recognize up to 100 regular clients of various species. They even can remember when each client had their last appointment (individuals who haven’t visited in a while are prioritized). Clients likewise remember their designated cleaner and may drop by up to 144 times per day—not because they have an exceptional load of parasites to remove, but apparently because they enjoy the caresses of their cleaner’s fins. “They [visit] because they want to,” Balcombe says. Fishes even seem aware of us as individuals. Captive fishes have been known to recognize the humans who feed them and ignore those who do not. Balcombe recalls a pinktail triggerfish named Furchbar, for example, who learned to pick up a pebble with his mouth and tap on the glass to get his owner’s attention around feeding time—demonstrating not just interspecies communication but also tool use. Likewise, researchers studying archerfishes found that, when presented with two human faces, the animals readily learned to identify the person that was paired with a food reward. Even wild fish can come to know and recognize humans. Moray eels, groupers, and sharks often form bonds with regular divers and, like an eager dog or cat, will approach their ungainly land friends for chin scratches and belly rubs. Most likely, we will never fully understand fish or know all there is to know about them. As Hardt points out, we’re still discovering new species, let alone coming close to cracking the mysteries of their biology. “To fully understand a fish, you would have to be a fish, I think,” Kramer adds. “They’ve kept me busy all my adult life, and the questions never seem to finish—never, ever.” Read Rachel Nuwer’s commentary piece on this story here .

Photo credit: Public Domain