Fish Say the Darndest Things

Intrigued by noises of the deep, scientists are using increasingly sophisticated equipment to detect and decipher the meaning of fishes' grunts, pops, knocks, croaks, moans and more

• Susan Goodman
• Feb 01, 1996

Phillip Lobel wasn't expecting actual sounds of passion in 1988 when he first eavesdropped on the hamlet, a species of coral-reef fish. He did know that fish make sounds: Ever since the Navy consulted biologists to help decipher alarming underwater noises during World War II, researchers had been confirming that some fish grunt, click or make other racket during courtship and threat displays. But Lobel was in search of telltale noises of the mating act itself, and he assumed they would come in the form of a hydrodynamic sound — distinctive swishes of tails or fins. His goal was to measure fish reproduction without cutting fish open to peek at gonads or scooping up and counting larvae. The known sounds of courtship were potentially useful, but they sometimes spanned days; he wanted to pinpoint spawning.

So Lobel, an ichthyologist at Boston University's Marine Program in Woods Hole, Massachusetts, hooked up a video camera with an underwater microphone sensitive to low frequency sounds and a radio transmitter to send data to the lab. He called the device a "spawn-o-meter." Then he dove into waters off Jamaica and recorded hamlets. Back at the lab, after digitizing the hamlets' signals for analysis, he had one of those Eureka! moments. "I thought they were only going to produce turbulence sound with their fins," he says. "And I was amazed to find they were producing a sound from within their bodies at that critical moment when they were broadcasting their gametes, releasing their eggs and sperm." These hamlets were singing songs of love which, translated into terms of human technology, were beeps and pulses ranging from 350 to 650 hertz, or cycles per second. Human voices regularly include such frequencies; middle C, for example, is 256 hertz.

Since that first discovery in 1988, Lobel and his colleagues have listened in on 30 other fish species in various locations, and many of his subjects have turned out to make sounds during actual mating. The discovery is the stuff of which science is made, a payoff from untold hours of patient work in the ocean and the laboratory, a painstaking addition to a growing body of research on fish noises and fish communication. Says longtime fish-communication expert Arthur Myrberg, Jr., professor of marine science at the University of Miami, "Lobel's work is raising the awareness, again, that sound production is important in the lives of fishes, and it is possible that we humans may be able to make use of that information as well."

Such findings have implications for improving fish management and conservation — and for yielding a greater understanding of fish as individuals and in their social interactions. Using fishes' mating or courtship noises to pinpoint the where and when of a species' reproduction, conservationists could conceivably target certain regions to protect during breeding season. With enough hydrophones and sophisticated sound analysis, biologists may one day better estimate yearly fish reproduction, and reproductive rates might serve as an index for the effects of noise and chemical pollution. In addition, the more scientists learn about the importance of communication among underwater creatures, the more we humans realize the toll we may be taking with our boats and ocean drilling.

Anyone who has spent time around aquatic creatures knows that many of them make sounds. Snapping shrimp snap, and lobsters buzz. The songs of whales have gone from the bottom of the sea to the top of New Age music charts. Each spring, when the male midshipman, a close relative of the toadfish, advertises for mates off the West Coast, new boaters invariably call talk shows, newspapers and local aquaria to report a strange humming they interpret as a naval experiment or an underground earthquake. "We now know that hundreds of fishes produce sounds," says Myrberg. And many species, such as groupers that can alarm even skin divers with booming noises, make sounds — whether of fear or warning — when approached.

Still, fish are hardly clamorous windbags. They're quite discreet about making noises; they have to be, especially when they spawn. "Fish are in a medium where sound travels about five times faster than in air and for much greater distances," Lobel explains. "Furthermore, all animals are 'distracted, otherwise engaged' while mating, so they are vulnerable to predators. Movies always have the monsters hanging out in Lovers Lane for good reason."

But in the murky underwater world, sound can be worth the risk. A specializedchirp can distinguish one species from another or help a female choose the best mate amongst several candidates. A squeal might synchronize the release of eggs and sperm to ensure greater fertilization. Such sounds are usually less than a half-second long and at a very low decibel level. "The whole mating game is like what goes on in submarine warfare," Lobel says. "Think about the movie The Hunt for Red October. You want to produce a signal but only when the receiver you're interested in is going to get it. You want to communicate without advertising your position."

Some fish stridulate, moving spines and fins in sockets to creak or to sound, as Lobel puts it, "like a rasping file." Others make the hydrodynamic sounds Lobel first looked for, like those made by the rapid fin movement of the striped parrotfish on its way to breed. Most, however, make drum-like sounds by vibrating muscles against their swim bladders, an air-filled sac in their abdomens. The resulting sounds vary in timbre, number of pulses and intervals of dead space to produce the low growl of the cichlids, the chirp of the domino damselfish, the croak of the croaking gourami. And the noises have different meanings. Long-spine squirrelfish grunt when fighting, for example, and make a staccato noise when predators come near. Seahorses snap while exploring new situations; gobies snore when intruders come into their territory.

Researchers have discovered that real communication is going on, with experiments like one conducted by Indiana University biology professor Bill Rowland with the jewel cichlid in 1979. By inserting tiny speakers in fish dummies and recording the response from live fish, Rowland demonstrated that while white noise emanating from the dummies evoked some reaction from his subjects, fish noises evoked a far stronger response: purring and thumping sounds, along with head nodding, gill flaring and fin spreading. "So I showed the sounds were paired with visual displays, too," says Rowland.

Despite all such evidence, Lobel warns against assuming that all fish are chatterboxes. "There is no way we can generalize and say that all fish produce sounds just because we know some do," he says. "Fish may seem very similar to each other because their 'design' was restrained by the need to swim through water. But in terms of evolution, they're quite diverse. Guppies are about as different from tuna as elephants are from dolphins. The latter two are both mammals, but you'd never generalize about their behavior. I think the basic rule of thumb is that if anything can be done in nature, it has probably evolved."

To confirm that fish respond in consistent ways to certain sounds and not to other cues will require more playback experiments in which underwater speakers produce the sounds and scientists track fishes' reactions, just as Rowland did with the jewel cichlid in laboratory tanks. Of course, the more natural the research conditions, the better, so Myrberg and colleagues took a step forward in a mid-1980s study when they found that female bicolor damselfish in the waters off the coast of Florida were able to choose between certain males by differences in their sounds. "In essence," says Myrberg, "one male had a high voice, and one had a low voice — and the females went to the male with the low voice. It's not important that they went to the low voice; it's just important they chose one of the two sounds consistently."

Predicts Lobel, "I'd wager that future research will find fish matching the complexity of communication we see in birds." And no matter how far the research leads, he hopes the songs of the deep will help change people's attitudes toward the chorus singing them. "People have never thought of fish in the same way as other pets or animals," he says. "Once you've seen fish interacting, mating and making sounds, when injured, you stop seeing them as dumb, mute creatures. You realize they deserve a little more respect."

Fish Call Function
Elephant-nosed mormyrid Clicks Aggression
Comely shiner Knock Male initiation of courtship
African jewelfish Purr or burr Male aggression in early courtship and during parenthood
Tetra Croak Male courtship
Bicolor damselfish Pop Combative confrontations
Gray angelfish Moan Recognition, maybe between a pair
Massau grouper Boom Aggression
Longspine squirrelfish Grunt Aggression
Seahorse Snap While exploring new situations
Toadfish Boat-whistle Male courtship call
Compiled from Various Sources

Peaceful Aquarium? Don't Bet on It!

There's a reason that loud, low-frequency sounds work to drive fish away from intake pipes of hydroelectric power plants. Now think of how the noises in your aquarium may be affecting your pet fish. Says ichthyologist Phillip Lobel, "A lot of people say their fish are catatonic in the corner of a tank, something that would typically happen if an animal was driven bonkers by noise."

Fish are exposed to the noise of an aquarium's air pumps and filters, vibrations conducted through floors, a room's stereo and television. Aquarium owners can reduce vibrations by inserting foam between the tank and its stand. Also, move pumps away from the tank, and separate filters from the tank with padding.

Boston writer Susan Goodman is author of two children's books. The latest is Unseen Rainbows, Silent Songs: The World Beyond Human Senses (Atheneum, 1995).