The underwater world is often perceived as silent, a misconception that portrays fish as quiet inhabitants. However, fish actively produce a diverse array of sounds for various purposes. These sounds, ranging from low rumbles to high-pitched clicks, are an integral part of their complex lives. Understanding how and why fish vocalize reveals a fascinating aspect of marine biology.
Mechanisms of Sound Production
Fish employ several distinct biological mechanisms to generate sounds. One primary method is stridulation, where they rub together bony parts of their bodies. Examples include marine catfishes, which produce squeaking sounds by rubbing specialized pectoral fin spines against their pectoral girdle. Seahorses also use stridulation, creating clicking noises by rubbing edges of their skull. This action, similar to crickets rubbing their legs, produces higher-pitched sounds, ranging from 1000 to 4000 Hz.
Another mechanism involves the swim bladder, a gas-filled organ. Many fish species possess specialized “sonic muscles” attached to or near this bladder. These muscles cause the swim bladder to vibrate rapidly, amplifying the sound. Fish like drums and croakers are well-known for their low-frequency drumming sounds, which can range from approximately 45 to 300 Hz.
The sonic muscles can be either intrinsic, attaching directly to the swim bladder, or extrinsic, originating on other structures like the skull or vertebrae and connecting to the bladder. This rapid vibration produces pulsatile sounds or continuous tones. For instance, the oyster toadfish utilizes intrinsic sonic muscles to produce a “boat whistle” sound, a continuous tonal call. Some catfish species can use both swim bladder vibration and stridulation mechanisms.
Purposes of Fish Sounds
Fish sounds serve various communication purposes in their aquatic habitats. Acoustic signals are used in reproductive behaviors, such as courtship and spawning. Male fish, like the black drum, produce loud, low-pitched sounds to attract females to spawning grounds. The oyster toadfish males also build nests and vocalize to entice potential mates.
Sounds also play a role in territorial defense, warning off rivals and protecting established areas. Damselfish, for example, are highly territorial and use sounds to deter intruders from their spaces. Aggressive displays may involve sound production to signal dominance or to defend resources like food.
Beyond reproduction and territory, fish use sounds for general communication within their species. This includes alarm calls to signal danger to other fish, such as clownfish warning their colony of a predator. Some sounds aid in navigation or maintaining social cohesion within groups, like herring producing “fast repetitive ticks” to coordinate schooling. Some fish, like goldfish, use their hearing to sense their surroundings and orient themselves.
Detecting Fish Sounds
Most sounds produced by fish are not audible to the unaided human ear. This is due to their low frequency or intensity, often falling outside the range of human hearing. Humans hear sounds from 20 Hz to 20,000 Hz, while most fish detect sounds from 40 Hz up to 1,000 Hz, though some species, like herring, can perceive frequencies up to 3,000 Hz.
Scientists primarily use hydrophones, which are specialized underwater microphones, to detect and record fish sounds. These devices convert underwater sound waves into electrical signals, allowing researchers to listen to and analyze the aquatic soundscape. Hydrophones can be deployed on buoys, fixed to the ocean floor, or attached to animals, providing continuous data collection over long periods.
Analyzing these recordings helps scientists identify specific fish species and understand their behaviors. By studying fish sounds, researchers gain insights into population health, distribution, and the impacts of environmental changes. This non-intrusive monitoring method contributes significantly to conservation efforts and the broader understanding of marine ecosystems.