My goldfish roommate hates when people tap on his tank. The tapping sound he hears in the water is loud and scary.
I talked with my friend Rikeem Sholes about how fish hear. He’s a fish scientist. He studies salmon hearing at Washington State University.
He told me that a fish’s hearing system includes sensory cells in the inner ear and in a line along the outside of the fish’s body and head. Some fish also use their swim bladder to have super hearing.
“A lot of people don’t realize that fish have ears,” Sholes said. “Fish don’t have external ears like we do. But they do have an inner ear that looks a little different from ours.”
Your external ear is the flappy part attached to your head. It helps you collect sounds from the air. But the sounds fish hear travel through water. So, fish ears are under their skin.
Three dense stones sit inside a fish’s ear—called otoliths or ear stones. They’re made of calcium carbonate just like bones.
Tucked under those ear stones are sensory cells called hair cells. They’re not really hair. They just look like tufts of hair under a microscope. Hair cells send electrical signals to the fish’s brain.
Sound moves through the water and into the fish’s body as a vibration. The vibration hits the ear stones and makes them move. As they move, the hair cells under the ear stones bend. When they bend, they send electrical signals to the brain. The brain uses that signal to understand what sound it’s hearing and where the sound comes from.
Fish also have hair cells on the outside of their bodies. They circle around a fish’s head and eyes. They make a long row down the fish’s side called the lateral line.
The hair cells of the lateral line are like feelers. As a fish swims, the water can bend those hair cells. That sends a signal to the fish’s brain—just like the hair cells in their ears do. The lateral line helps fish swim in a school. It also helps them detect prey or predators.
Some fish can hear extra well, thanks to their swim bladder. That’s a sack of gas in the middle of a fish’s body—like a balloon. It helps a fish float or sink depending on how much air is inside it. That’s how a fish moves up or down in the water.
Some fish have a connection between their swim bladder and their ears. For them, the swim bladder amps up sound vibrations that hit the ear stones.
“It amplifies their ability to hear—like super hearing,” Sholes said.
Maybe that’s why tapping bothers my goldfish so much. We can protect our fish friends by being careful about the human-made sounds they hear in enclosures and in the wild. Thinking about how we affect other animals and ecosystems helps us all get along swimmingly.