Seahorses are among the most recognizable and unusual fish in the ocean. Their slow, deliberate movements often lead to the assumption that they are silent creatures inhabiting a quiet underwater world. However, research using specialized hydrophones has revealed that seahorses are not mute, but produce vocalizations using a specific physical mechanism for distinct purposes.
The Nature of Seahorse Sounds
Seahorses produce two primary types of acoustic signals: clicks and growls. The most common sound is the “click,” a rapid, low-frequency pulse often associated with feeding and social interactions. These clicking sounds typically register frequencies between 50 and 800 Hertz and are usually too quiet for humans to hear without specialized listening devices.
A second, less frequent sound is the “growl,” a series of low-frequency pulses concentrated below 200 Hertz. Growls are often accompanied by body vibrations and are primarily recorded when the animals are under duress. Both males and females are capable of producing these sounds, making acoustic signaling a shared trait within the species.
How Seahorses Physically Produce Noise
Unlike many other fish that use their swim bladders to create sound, seahorses lack this mechanism for vocalization. Instead, they produce noise through a mechanical action known as stridulation, which is the act of rubbing two bony parts together. The sound-producing apparatus is located in the head structure.
The clicking sound is generated by the articulation between the supraoccipital ridge of the neurocranium (part of the skull) and the grooved anterior margin of the coronet. The coronet is the crown-like structure situated on the top of the head. When the seahorse rapidly moves its head, these two bony elements slide and knock against each other, creating the sharp click.
This stridulatory mechanism has been confirmed through surgical manipulation, which showed that modifying the supraoccipital-coronet joint decreased the proportion of clicks produced during feeding strikes. While the growl is distinct, it is believed to be produced by a different mechanism. This potentially involves vibrations in the cheek or a different structural component, though the click mechanism is the most studied.
The Purpose of Their Vocalizations
Seahorse sounds serve two distinct behavioral functions: one related to sustenance and the other to communication. The clicks produced during feeding are closely linked to the seahorse’s rapid suction feeding strike. When a seahorse snaps its head forward to catch tiny prey, the quick head movement triggers the stridulation, making the click a consistent byproduct of the strike.
Acoustic signals are also deliberately used during complex social interactions, most notably in courtship and mating displays. Courtship clicks are often louder and more frequent than feeding clicks, with the highest abundance recorded on the final day of the courtship process. Researchers suggest this signal may function as a courtship call, signaling readiness to mate and helping to synchronize the pair’s actions.
The “growl” sound, produced when a seahorse is captured or handled, appears to be a distress or defensive warning. This low, vibrating sound may function to startle a potential predator, allowing the seahorse a chance to escape. The existence of these distinct sounds in different contexts suggests that seahorse vocalizations are an important part of their behavioral ecology.