Many years ago I was told that drum fish communicated by shaking their heads violently, which caused their otoliths (earstones) to rattle; indicating that only Drums had otoliths and that, somehow, they could decipher rattles. The same person also told me the fish had earned its name “Drum” because of the drumming sound produced while shaking its head. To prove his point, my instructor dissected a fish, removed the otoliths, and shook them in a bottle so that I could hear the noise—although not until after shaking the whole fish in my face while asking, “Can you hear it?” several times—which I couldn’t.
Although he was trying to be helpful, it turns out that his information, some 30 years past, was incorrect. All fish species, with the exception of rays, sharks, and lampreys, have otoliths or earstones. Since the earstones grow in ring-like patterns, much the way trees grow, they are invaluable when aging a fish. And, not only do the earstones, comprised mainly of calcium, aid in the fishes’ sense of balance but they also give the fish a means of hearing much like the bones in our human ears.
So why does a fish need to hear? It seems they have been talking to each other for millions of years. The drums, both freshwater and salt, do not swim around shaking their heads and rattling their brains. Instead, their communication is much more sophisticated; they grunt, hum, and growl like most other fish species.
The common misconception, even amongst many scuba divers, is that the underwater world is a silent place. But sit very still on the bottom, especially near coral reefs, and the underwater world is rife with a cacophony of sound. Or, stay dry and invest in (or build) an inexpensive hydrophone and those willing to listen carefully will be amazed.
In a recent paper published in the journal Science, three visiting professors at the Marine Biological Laboratory, a branch of Woods Hole Oceanographic Institute in Massachusetts, presented the findings resulting from a five-year study of fish communication. According to the paper, Dr. Andrew Bass of Cornell University, Dr. Robert Baker of New York University Medical Center, and Dr. Edwin Gilland of Howard University studied the neuroscience and physiology of sounds created by a male Midshipman fish.
What they discovered is that the neural circuitry responsible for sound in fish is quite similar to that which allows a child to giggle or a horse to neigh. “Fish have all the same parts of the brain that you do,” says Bass, the paper’s lead author. Bass further states, “There’s reason to suggest that the use of sound in social communication is widespread among fishes.” Additional conclusions of the fish communication study also show “evidence that the ability to make and respond to sound is an ancient part of the vertebrate success story.”
It seems that the male Midshipman fish, a close relative of Toadfish, cannot attract a mate to the stone nest he creates unless his humming song finds the ear of an approving female. No song, no mate. In an article published by the MBL at Woods Hole, Dr. Bass, the lead scientist, stated, “Fish are an incredibly successful group, making up nearly half of the living species of vertebrates, and vocal communication may be partly responsible. The kind of work we’re doing contributes to answering questions as to why these animals are so successful. We’re only touching the tip of the iceberg here.”
How do fish create the sounds? Most all fish, sharks being one exception, have a swim bladder (also called a gas bladder or air bladder) which is a gas-filled organ located dorsally that controls buoyancy by contracting and expanding as the fish travels through the water.
But, the swim bladder serves a dual purpose. Its second function is that of creating sound. When the fish need to warn an intruder away from nest areas or attract a female to newly built nests, neurons in the brain dedicated to communication signal the vocal muscles around the swim bladder to contract and the appropriate grunt, growl, or hum is produced; much like our communication neurons tell our vocal muscles to contract when we have need to communicate.
Just imagine all the conversations going on below the surface. There’s still so much to learn about our seas and the creatures within and, just maybe, along the way more of us will realize how many basics we share. It wasn’t that long ago that we thought only man had the ability of language. Now we find that even fish have language.
After 30 years as a wild and domestic animal rescuer, rehabber, and educator in the states, Becky Dayhuff-Bauer became a scuba instructor and award-winning journalist covering the marine environment in the Caribbean. She is a contributing photographer to NOAA.