The aquatic world, often perceived as silent, is a surprisingly noisy place filled with a constant chorus of biological sounds. Contrary to the common belief that fish are mute, many species actively produce a variety of noises ranging from low-frequency rumbles to sharp clicks and chirps. This vocal behavior serves as a primary form of communication, especially where visual cues are limited by darkness or murky water. The ability of fish to generate and perceive sound indicates that acoustic signaling plays a substantial role in their social lives and survival.
The Biological Mechanisms of Sound Production
Fish employ two principal anatomical methods to generate sounds: internal vibration or external friction. One common method involves the rapid vibration of the swim bladder, a gas-filled organ used for buoyancy control. Specialized “sonic muscles,” which are among the fastest-contracting muscles found in vertebrates, attach directly to the swim bladder wall. These muscles contract and relax at high speeds, causing the bladder to resonate and produce sounds often described as “drums,” “rumbles,” or “honks.” The black drum and oyster toadfish use this drumming mechanism to create low-frequency calls, typically below 300 Hz.
The second major mechanism is stridulation, which involves the rubbing or grinding together of bony or skeletal parts. Similar to how crickets produce sound, a fish rubs a rough surface against a rigid structure, creating a raspy or clicking noise. Many catfishes stridulate by rotating the spine in their pectoral fins against a groove in their shoulder girdle. Other species, like the grunts, produce sound by gnashing their pharyngeal teeth located in the throat behind the gills. These stridulatory sounds tend to have a higher frequency range, often peaking between 1000 and 4000 Hz, and are typically short, sharp pulses.
The Reasons Fish Communicate Acoustically
The intentional sounds produced by fish serve distinct purposes, primarily revolving around reproduction and social interactions. Acoustic signals are integral to courtship and spawning rituals for many species, often restricting sound production to breeding seasons. Male fish, such as the Lusitanian toadfish, generate specific calls like the “boatwhistle” to attract females to their nesting sites. These vocalizations convey information about the male’s readiness to mate, size, and fitness, allowing females to make selective choices.
Acoustic communication is also utilized for territorial defense and aggressive displays against rivals. When defending a nest or feeding territory, a sudden burst of sound acts as a warning or “keep-out” signal to deter intruders without physical conflict. Damselfish, for example, produce distinctive clicks and chirps by grinding their teeth during aggressive encounters to assert dominance. Resident males who vocalize are significantly more successful at warding off competitors than those whose sound production is artificially muted.
Fish also use sound during times of stress, distress, or for coordination within a group. Startle responses or sounds emitted when a fish is attacked by a predator or caught may serve as an alarm to nearby conspecifics. The collective vocalizations of schooling fish may also play a role in maintaining group cohesion, especially in dark or turbid conditions where visual cues are ineffective. The prominence of sound in these contexts highlights its importance as a reliable, long-distance communication channel in the underwater environment.
How Scientists Record and Interpret Underwater Noise
The field of bioacoustics relies on specialized technology to capture the subtle sounds of fish beneath the water’s surface. The primary tool is the hydrophone, an underwater microphone that converts pressure waves into electrical signals for recording and analysis. Scientists often deploy hydrophones for long-term passive acoustic monitoring (PAM) to record ecosystem sounds over extended periods, including the nocturnal choruses of spawning fish. This technique allows for the study of fish behavior without direct disturbance.
Interpreting the recorded data is challenging due to the high volume of ambient noise in the ocean. The underwater environment is constantly filled with sounds from snapping shrimp, waves, and noise pollution from vessel traffic. Researchers analyze the spectral patterns of fish sounds, looking at characteristics like frequency, duration, and pulse repetition rate to distinguish species-specific calls from background noise. Newer methods incorporate machine learning algorithms to automatically identify and classify fish calls, speeding up the analysis of acoustic data.
In advanced studies, researchers combine hydrophones with 360-degree cameras to visually link a specific sound to the fish that produced it. Accurately pinpointing the source is complex because sound travels much faster in water than in air. These innovations help build a comprehensive library of fish vocalizations. This growing body of knowledge is instrumental for monitoring the health of aquatic habitats and tracking the presence of species that are otherwise difficult to observe.