The common perception of the underwater world as a silent realm is inaccurate. Fish, much like land animals, actively produce sounds, engaging in complex acoustic communication for diverse purposes. This ability to generate sound is widespread across numerous species, indicating its significance in their daily lives beneath the surface.
How Fish Produce Sounds
Fish employ several biological mechanisms to create sounds. A primary method involves the swim bladder, a gas-filled organ. Many species, such as drums and croakers, possess specialized sonic muscles attached to or near this bladder. These muscles cause the swim bladder to vibrate rapidly, producing sounds like grunts, croaks, hums, and thumps. The swim bladder acts as a resonating chamber, amplifying these vibrations into audible sounds.
Another common mechanism is stridulation, which involves rubbing together hard body parts. Fish can produce sounds by grinding their oral or pharyngeal teeth, or by rubbing fin spines against skeletal elements. Examples include marine catfishes using pectoral fin spines against their pectoral girdle to create squeaking sounds, and seahorses clicking by rubbing skull components. These stridulatory sounds often result in clicks, rasps, or creaks.
Hydrodynamic sounds are also produced by some fish through rapid body movements. These sounds are low-frequency thumps or pops generated when a fish quickly changes direction or velocity. While sometimes a byproduct of swimming, such sounds might play a role in predator-prey interactions. For instance, rapid movements during spawning can also generate hydrodynamic noise.
The Purpose of Fish Sounds
Fish use sounds for a range of communicative functions essential for survival and reproduction. Courtship and mating represent a significant context for sound production. Male fish often produce specific calls, such as the “boat whistle” of the oyster toadfish, to attract females to nests and synchronize spawning. These acoustic signals convey information about male quality, including size and condition.
Sounds also serve in territorial defense, allowing fish to ward off rivals and protect their space. Species like damselfish use sounds to deter intruders from their territories. These acoustic signals can be effective over longer distances or in murky waters where visual cues are limited. Fish can also express aggression through sounds like growls or knocks when fighting.
Warning and alarm signals are another important use of fish sounds. Some fish emit sounds to alert others to the presence of predators or danger. Certain fish may also produce sounds when captured or stressed. Sounds can also contribute to group cohesion, helping maintain school integrity and aiding in coordinated foraging activities.
Hearing the Underwater Symphony
Most fish sounds are low-frequency, below 1000 Hz, and are not directly perceptible to the human ear without specialized equipment. This is due to how sound propagates in water and the limitations of human hearing. Researchers utilize underwater microphones, known as hydrophones, to record these diverse vocalizations.
The sounds documented from fish are varied, extending beyond simple grunts. They include pops, clicks, whistles, purrs, growls, croaks, hums, barks, and even rattles. Many species, such as the American codfish, have distinct sounds. The study of these underwater sounds, including those made by fish, falls under the scientific discipline of marine bioacoustics.
Despite the common human perception of a quiet underwater world, aquatic environments are acoustically rich and complex. This vibrant soundscape underscores the intricate communication networks that exist among fish, revealing a hidden world of acoustic interactions that scientists continue to explore.