Though the aquatic world often seems silent to human ears, fish do make a variety of sounds for different purposes. Unlike many land animals, however, fish do not possess vocal cords.
The Absence of Vocal Cords
Fish do not possess vocal cords, the specialized structures found in the larynx of many land vertebrates. These cords vibrate as air passes over them, creating sounds. Unlike mammals, birds, and some reptiles that breathe air using lungs, fish respire by extracting oxygen from water using gills. Their aquatic respiratory system does not involve the air passage necessary for vocal cord vibration. Instead, their sound production mechanisms are entirely different, leveraging unique anatomical features.
How Fish Produce Sounds
Fish employ diverse anatomical structures to generate sounds, often utilizing internal organs or by rubbing body parts together. One common method involves the swim bladder, an internal gas-filled organ that helps fish maintain buoyancy. Some fish species have specialized muscles that rapidly vibrate their swim bladder, producing sounds such as grunts, drums, or croaks. Male toadfish, for example, are known for their distinct “boatwhistle” calls, generated by rapid contractions of muscles attached to their swim bladder, which can occur at rates exceeding 100 times per second.
Stridulation and Hydrodynamic Sounds
Another significant way fish create sounds is through stridulation, involving rubbing together bony structures like fin spines against the pectoral or dorsal girdle, or grinding pharyngeal teeth. Catfish, for instance, often produce sounds by locking and rubbing their pectoral fin spines within their sockets, creating rasping or creaking noises. Similarly, many species of damselfish and parrotfish generate clicking or scraping sounds by grinding their pharyngeal teeth. Hydrodynamic sounds also result from rapid movements through the water, such as sudden accelerations. These sounds, while often less intentional, still contribute to the underwater acoustic environment.
Purposes of Fish Sounds
Fish produce sounds for a range of biological purposes, making acoustic communication a significant aspect of their behavior. One primary reason is communication within their own species, which can facilitate various social interactions. During reproductive periods, many fish species use sounds for courtship, with males often emitting calls to attract mates or to signal their readiness to spawn. For example, some cod species produce grunting sounds during spawning aggregations.
Sounds also serve as a means of territorial defense, where fish emit warning signals to deter rivals. Certain fish may also use sound as a predator avoidance mechanism, either by startling a potential threat or by signaling danger to other fish, creating an alarm response. Sounds can also be associated with foraging activities. The effectiveness of sound communication underwater is amplified by how sound travels much faster and further in water compared to air, making it an efficient medium for transmitting information across distances.