Several years ago, scientists noticed, and were mystified by, a high pitched buzzing sound that stood out against the background noise of the deep Pacific Ocean. Now the cause has been revealed: the sound is associated with the nightly vertical migration of millions of small fish that rise at dusk to feed near the surface and descend again before dawn. The reason for the noise is not known, it might be an unintentional byproduct of pressure changes during the migration or it might be a form of communication. Either way, it is consistent with a little known fun fact—fish are surprisingly noisy.
Fish noises include the explosive sounds made by gas release in herring and the rhythmic drumbeat of redfish. Even tiny larval fish are in on the act: transparent, centimeter-long baby snappers make grunting sounds at night, possibly to help maintain group cohesion.
More familiar to coastal residents are the whistles and croaks of slimy midshipmen and toadfish in the intertidal zone. As biologist Andrew Bass explains, the breeding season for these fishes is definitely not quiet time. Male midshipmen, for example, attract mates with a humming sound that can last up to an hour. Toadfish employ a high-pitched whistle for this purpose. Both species employ shorter grunts or barking sounds to frighten rivals during conflicts. During breeding season, theses sounds are so persistent that California anglers have nicknamed the midshipman “canary fish.”
How are these sounds produced? Over 50 families of marine and freshwater fish can vocalize by one of two mechanisms. One method is stridulation, or sound produced by rubbing two body parts together. Some fish have pharyngeal teeth located in the back of the throat arch. When these are rubbed together, a chattering or grunting sound results. Swim bladders, organs used by many fish to regulate buoyancy, can resonate and amplify theis sound.
In other fish, specialized muscles expand or contract the swim bladder, producing a drumming or throbbing. There is, in fact, a particularly noisy family of fish called the Drums, or Sciaenidae. These muscles tend to be more pronounced in the larger breeding males than the quieter females or smaller males. Male toadfish have been recorded at 120 decibels, louder than a rock concert.
The migratory hum was originally discovered while scientists were listening for more pleasant ocean noises, such as whale songs. Clearly, when it comes to noise, the whales have a lot of company. Given all the racket, it’s amazing marine animals can hear themselves think underwater.