It is a common misunderstanding that the underwater world is quiet and that fish lack the ability to hear. Fish do hear, and their auditory capabilities are important for their survival in aquatic environments. While their hearing mechanisms differ from humans, sound is a significant sense for fish, providing information across wide areas and varying light conditions.
How Fish Sense Sound
Fish possess two primary sensory systems for detecting sound: their inner ears and the lateral line system. The inner ear, located within the skull, contains dense calcium carbonate structures called otoliths. Unlike the fish’s body, which has a similar density to water, otoliths are much denser, causing them to move at a different amplitude and phase in response to sound waves. This differential movement between the otoliths and the surrounding sensory hair cells bends the cilia, which are then interpreted by the brain as sound.
Sound travels differently in water than in air, moving much faster and propagating over greater distances. This makes underwater sound an important information source for aquatic animals. Many fish species also utilize a gas-filled swim bladder to enhance their hearing sensitivity. The swim bladder acts as a resonator, amplifying sound vibrations and transmitting them to the inner ear. Some fish, such as carp and minnows, have a specialized skeletal structure called the Weberian apparatus, which connects the swim bladder directly to the inner ear, further boosting their ability to detect sounds.
Beyond the inner ear, the lateral line system provides another means of detecting underwater disturbances. This system consists of a series of mechanoreceptors, known as neuromasts, found along the fish’s head, trunk, and tail. These neuromasts contain hair cells that detect water movement, vibrations, and pressure changes. The lateral line is particularly effective at detecting low-frequency vibrations, typically below 200 Hz, and is sensitive to movements within one to two body lengths of the fish. While the inner ear is responsible for true “hearing,” the lateral line complements this sense by providing information about nearby movements and water displacement.
The Sounds Fish Perceive
Fish perceive a variety of sounds, with their typical hearing range extending into lower frequencies. Many fish species can detect sounds up to 800-1000 Hz. Some generalist species typically hear sounds up to 1,000 to 1,500 Hz. However, “hearing specialists,” like goldfish, carp, and catfish, possess a broader hearing range, detecting sounds up to 4-8 kHz and with greater sensitivity to quieter sounds.
A unique adaptation in some clupeid fish, such as herring and American shad, allows them to detect ultrasound, with frequencies exceeding 10,000 Hz. This capability helps them detect the echolocation clicks produced by hunting dolphins. Fish perceive sound as both particle motion—the back-and-forth movement of water molecules—and pressure waves. All fish are capable of detecting particle motion, but only those with gas-filled organs like a swim bladder can also detect the pressure component of sound. Natural sounds fish might perceive include:
- Movements of predators
- Rustling of prey
- Communication from other fish
- Environmental sounds like waves or geological events
Why Hearing Matters for Fish
Hearing is an important sense that allows fish to navigate and survive in their underwater environments. It plays a role in detecting predators, enabling fish to perceive threats and initiate escape responses. This sense also assists in locating prey, as fish can detect the vibrations and sounds produced by potential food sources.
Beyond foraging and defense, sound helps fish with orientation and navigation. They can use acoustic cues for habitat selection and to guide migrations. Sound is also important to communication among fish, facilitating various behaviors such as mating calls, territorial displays, and maintaining cohesion within schools. The ability to discriminate between sounds of different amplitudes, frequencies, and temporal characteristics allows fish to recognize individuals of their own species and distinguish between various acoustic signals.
Noise and Fish Health
Human-generated noise has introduced a new challenge to the underwater acoustic landscape, potentially affecting fish health and behavior. Sources of this anthropogenic noise include:
- Commercial shipping
- Sonar systems
- Offshore oil and gas exploration
- Pile driving
- Dredging
- Other industrial activities
These sounds can travel long distances underwater, impacting large numbers of fish.
Excessive underwater noise can disrupt fish behavior, leading to changes in activity patterns, increased aggression, or avoidance of important feeding and breeding grounds. It can also induce physiological stress responses, such as elevated stress hormone levels, which may reduce growth rates, immune function, and reproductive success. Noise can interfere with fish communication by masking natural sounds, making it harder for them to detect mates, predators, or prey. In some instances, intense noise can result in physical harm, including:
- Internal injuries
- Cellular damage
- Hearing loss
- Disorientation
- Even death
Such impacts have broader implications for fish populations and the ecosystems they inhabit.