Scientists have shown a fish that uses its head as a drum

Scientists from Louisiana State University have discovered that an unusual cavity in the skull of the fish Bothragonus swanii may be used for sound communication: the animal likely strikes it with its ribs, creating vibrations. The study of the species is presented on the university website (LSU).

Bothragonus swanii is a small bottom-dwelling fish that inhabits the intertidal zone of the northeastern Pacific Ocean. The creature's body is covered with a dense bone armor, which allows it to camouflage well among stones. The main feature of the species is a deep cup-shaped pit in the skull, comparable in size to the volume of the brain. Its purpose has long remained unclear.

Using high-resolution micro-computed tomography, researchers studied preserved specimens of B. swanii and related species. The analysis showed that the first pair of ribs in this fish is arranged in an unusual way: they are enlarged, flattened and mobile, not rigidly connected to the spine, and linked by tendons to some of the most powerful muscles in the body. These ribs come into contact with the bottom of the cranial pit, which is significantly harder than its walls.

According to the authors, this configuration allows the fish to quickly and forcefully strike the inner surface of the cranial cavity with its ribs, causing vibrations. These oscillations likely propagate along the bottom and serve for communication with other individuals that also move along the substrate rather than in the water column. This may be more effective in the noisy environment of tidal pools, where the sounds of waves and stones drown out normal acoustic signals.

Direct observations of such behavior and recordings of the sounds produced are not yet available, but the authors consider the proposed mechanism plausible and plan to verify it using underwater acoustic measurements.