On the heels of Valentine’s Day when people are playing romantic tunes and thinking fondly of their loved ones, there are some romantic tunes that resound underneath the water — if you are lucky enough to hear them. These are the songs of fish singing to their mates, or at least some of the sounds are romantic. Others are used for other types of communication and some are deemed “incidental” sounds that fish make as a result of their physiology or behavior.

Fish sounds don’t tend to be as dramatic as the vocalizations of whales or dolphins, but they can be quite varied and unique. Sounds include squeaks, grunts, chirps, drums, and pops, to name a few.

So, do fish have vocal cords? No. Instead of using vocal cords to make sounds, they produce sounds several different ways. The first is by rubbing their bones or teeth together and is called stridulation. Seahorses do this by rubbing the bones of their skull together. Other sounds can surprisingly come from a fish’s swim bladder. This is the gas-filled sac in a fish’s belly that helps it to adjust its buoyancy.

A fish can fill its swim bladder by gulping air when it is at the surface, which then weirdly passes down its esophagus into the bladder. In some fish, there is a muscle attached to the swim bladder that makes the bladder vibrate and make a kind of drumming sound. Other fish without this muscle might still make a noise as gas is released from the swim bladder when they descend from the surface — kind of like a fish burp.

Several fish in the Gulf of Maine make interesting sounds. Atlantic herring, for example, release air from their swim bladders in the opposite of a burp. Sound researchers have dubbed this a fast repetitive tick (FRT). It is thought that one of the purposes of the FRT is to communicate with each other in order to stay close while they are swimming in schools. Atlantic cod make low knocks and hums during spawning season. And, another local fish, the cusk, makes pronounced grunting sounds.

The sounds that fish make are not just useful to the fish themselves, but also are useful to scientists. Studying something that lives underwater is tricky. The sounds that they make can be an important tool for scientists attempting to track and manage fish populations. This is especially helpful when trying to identify when and where fish are spawning. One way to sample fish during spawning is to capture them and dissect them to look for eggs. This is obviously less than ideal. So, being able to listen and tune in to when this is happening is very useful and much less harmful.

But it is not easy to hear fish underwater. The surface of the water acts like a giant sound mirror and keeps all that sound under the water. It doesn’t take much to listen in to some of what is being said, though. You can put your ear against the bottom of a boat and often hear clicks, pops and grunts. Or you can put a simple tube into the water and listen. Scientists use more sophisticated microphones called hydrophones that are specially designed to amplify sounds under water.

If you want to hear some amazing fish sounds, there is a great podcast on NPR’s Living Lab (capeandislands.org/show/living-lab-radio-on-cai/2018-12-10/fish-noises-help-scientists-locate-understand-them.) The DOSITS (Discovery of Sound in the Sea, .org/) also has a wide array of fish sounds.

There is always something mysterious and interesting happening under the water that we can only begin to understand. But it doesn’t take much to listen for what might be a love song. Or perhaps it’s just an overinflated fish bladder.