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Summer is here, and beaches and docks are full of the sounds of people having fun: splashing in the water, revving motor boats, thumping sand into castle shapes.
If you can find a quieter spot of water and stick your ears underneath, you might hear many other sounds made by fish.
People have known that fish make sounds since ancient Greece; that's why they gave some fish names like red drum, pig fish or croaker. "They're based on the sounds these fish make," says Audrey Looby, a fish-sound researcher at the University of Florida.
So far, about 1,000 fish species have been recorded making sounds. You can listen to some of them at a website called FishSounds, to which Looby will soon contribute. Her favorite-sounding fish is the Gulf toadfish.
Unlike birds, which make sounds in the same way, Looby says that fish evolved to make sounds many times during their existence. That means they make sounds in different ways. "Basically, they use whatever mechanism is easiest for them," she says.
Fish don't have specialized vocal cords, larynxes or vocal folds. So one of the most common ways they make sound is through tribulation — rubbing two pieces of bony structure together, "like clicking their teeth or rubbing their pectoral fins against other structures to make cricket(-like) sounds," says Looby.
Many others make sound with their swim bladders, which they use primarily to stay buoyant and level in the water. But, Looby says, "some fish have a sonic organ of some kind attached to this swim bladder, so they can (bang) on it and it resonates like a drum."
Scientists are unsure how many fish make sounds, but some estimate that it might be as many as 22,000 types, which is two-thirds of about 34,000 known species. And those are just the sounds fish make on purpose — to call to mates, to let other fish know they're in trouble or to communicate that "this is my area of the reef, listen to how tough I sound so why don't you just swim away," Looby says. Fish also make passive sounds, such as chewing noises as they munch on sea grass or algae.
According to Looby, active and passive sounds are important because they "convey a lot of information about what's going on" to fish and to researchers. Chewing sounds, for example, let anyone who's listening know that there's a food source available. And the mating and warning noises of certain fish species tell scientists information such as "how much diversity is on a reef, where invasive species are located, where endangered species are located," says Looby.
With climate change making parts of the ocean heat up and become unlivable for fish in other ways, researchers say that fish sounds could help them preserve and restore habitats. For example, there are projects looking into whether piping in the sounds of a healthy reef into one that is dying might encourage fish to come back and populate it.
Learning about fish sounds "lets us learn about (underwater) environments and hopefully manage them at the same time," Looby says.