Fish That Make Sounds—Purrs, Grunts, Hums and Hoots
The world below the ocean surface is often a noisy place, researchers say. At least one thousand types of fish – and probably many more - produce sounds. These vocalizations can take a wide variety of forms, including pops, clicks, whistles, purrs, grunts, groans, growls, barks, hums, hoots, rattles and even tinkles.
Fish produce sounds to attract mates, warn of danger, scare competitors and predators and maintain social cohesion. Some also create sound as a distress call. Although people have known for a long time that certain fish can vocalize, scientists have only recently realized how widespread this ability is.
Researchers record fish vocalizations with the aid of an underwater microphone called a hydrophone. This may be lowered into the water from a boat or carried by a scuba diver. Until recently, divers were unaware of the wide variety of fish sounds in the ocean because the sound of bubbles being released from scuba equipment masked the sounds produced by the fish. In addition, the bubbles often disturbed fish and caused them to swim away.
Fish sound researchers are now using rebreathers instead of conventional scuba gear. A rebreather is a self-contained system in which the diver repeatedly breathes in his or her exhaled air, so no gas bubbles enter the water. Carbon dioxide is removed from the exhaled air inside the rebreather. An oxygen sensor monitors the level of oxygen in the rebreathed air and a microprocessor controls the delivery of fresh oxygen into the air when it’s needed.
The Swim Bladder - The Key to Many Fish Sounds
Inside the abdominal cavity of most types of fish is a gas-filled sac called a swim bladder (the blue organ in the diagram below). The fish uses the swim bladder to control its buoyancy. When gas is added to the swim bladder the fish is more buoyant and can swim higher in the water. When gas is removed from the swim bladder the fish sinks in the water.
The swim bladder is filled in one of two ways. Some fish gulp air from the water surface. The air then passes through a duct connecting the esophagus to the swim bladder. The esophagus is the passageway that connects the mouth to the stomach. Other fish have a gas gland, which extracts gas from the blood and sends it into the swim bladder.
Internal Anatomy of a Fish
How Do Fish Produce Sounds?
In some fish the swim bladder is used as a sound-producing organ. A muscle attached to the swim bladder, called the sonic muscle, contracts and relaxes in a rapid sequence, causing the swim bladder to vibrate and produce a low-pitched drumming sound. The sonic muscle of the oyster toadfish is able to contract at a rate of 200 times a second!
Another way in which fish may produce sounds is by stridulation, a process in which hard body parts like teeth or bones hit each other. Body movements that create water currents or splashes are also used to create sounds for communication.
A Toadfish Sings in Honduras
Toadfish have a wide face that is reminiscent of a toad's and eyes that are located towards the top of the head instead of on the side as in most fish. They usually live on the ocean bottom, where they are ambush predators. They are generally colored and patterned to help them blend in with their background. Male toadfish are known for their habit of producing sounds to attract females.
The three-spined toadfish, or Batrachomoeus trispinosus, lives in the western region of the Pacific Ocean. It's the only fish so far known to produce non-linear sounds.
Normal sound is said to be linear. Non-linear sounds are more complex. Their sound waves cause unusual effects in the materials that they travel through. Non-linear sounds can produce intense sensations in humans and (apparently) in animals, too.
Crying babies and animals such as marmots and songbirds emit non-linear sounds as alarm calls and to communicate distress. Film makers use music with non-linear sounds in movies to evoke emotions like fear and tension in viewers.
Three-spined toadfish have a swim bladder that is divided into two sections, forming two functionally separate areas. Each half of the swim bladder is controlled by its own sonic muscle and can produce its own sound. When each section of the swim bladder emits a different sound at the same time the sound is said to be biphonic. Scientists are trying to discover what role the non-linear sounds play in the three-spined toadfish community.
Some Plainfin Midshipman Vocalizations
The midshipman is another type of toadfish and has the scientific name Porichthys notatus. The fish is notable for the bioluminescent spots on its surface, the sounds that it produces and the fact that it can breathe in air. Interestingly, not all plainfin midshipman are bioluminescent.
Plainfin midshipman are found off the west coast of North America from Alaska to Baja California. In California they are sometimes called “California singing fish”.
During the mating season the male midshipman hums – sometimes for long periods - by hitting his swim bladder with his sonic muscle. His humming is designed to attract a female. Once she deposits her eggs, the midshipman resumes humming to attract another female to his nest. The male guards the eggs until they hatch.
Researchers have discovered that there are two types of midshipman males – Type 1 and Type 2. Type 2 males are sometimes called “sneaker males”. They are smaller than Type 1 males and do not hum, although they can make other vocalizations. Instead, they try to sneak into the nest and quickly fertilize the eggs before the Type I males notice what they are doing.
The Plainfin Midshipman Fish
Black Drum Sounds
The black drum (Pogonias cromis) is a black or grey fish that lives in the brackish water found in areas such as estuaries. Black drums are mainly bottom feeders. The young fish have black stripes on a light background, but the stripes fade as the fish matures. Adults can become very big and may weigh over a hundred pounds.
Black drums become very noisy during the mating season. The low pitched sounds that they produce travel long distances. The males produce the sounds to attract females.
In 2005, residents in Cape Coral on the Florida Gulf Coast complained that they were being kept awake at night by low-pitched throbbing sounds in their homes, which they believed were being created by an engineering fault in the buildings. It was eventually discovered that the sounds were being created by black drum fish, which at first the residents found hard to believe. The fish had swum into the canals and estuaries in the area. Their mating calls were penetrating the ground and the seawalls and entering nearby houses.
Herring and Their Interesting Method of Sound Production
Herring communicate with each other by forcibly expelling gas from the anal area, producing bubbles and a high-pitched sound. The researchers call this sound production an FRT (Fast Repetitive Tick). They did have another word in mind when they created the term, however!
Both the Atlantic herring (Clupea harengus) and the Pacific herring (Clupea pallasii) produce FRT's. The fish gulp air from the water surface and then store it in the swim bladder. During the night, in darkness and when surrounded by other herring, air is released through the anal duct. The gas that is emitted isn't made from the digestion of food, since captive herring produce the sounds whether or not they have been fed.
Herring have a good sense of hearing. The purpose of the FRT sounds may be to ensure that the fish stay close together.
Listening to Fish Sounds
The “Discovery of Sound in the Sea” or DOSITS website was created by the University of Rhode Island. It contains a collection of audio files which play the sounds created by fish (including the black drum) and whales.
Other Fish Sounds
Both ocean and freshwater fish produce sounds. Seahorses produce clicking sounds by rubbing two parts of their skull together. The weakfish - a type of drum - produces a purr with its sonic muscle and swim bladder. Squeaker catfish rub the spines located in their pectoral fins into grooves on their shoulders. Talking catfish can produce sound in two ways - by vibrating their swim bladder or by vibrating their pectoral fin spines in their sockets.
Research of sound production in fish is still in its infancy. As scientists continue their investigations they are likely to find even more fish species that make sound and even more methods of fish vocalizations.
© 2011 Linda Crampton
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