One of the world’s smallest fish, measuring about the width of an adult human fingernail, can make a sound as loud as a gunshot, scientists have said.

The male Danionella cerebrum, a fish of about 12mm found in the streams of Myanmar, produces sounds that exceed 140 decibels, according to the study published in the PNAS journal, equal to an ambulance siren or jackhammer.

The most common mechanism in fishes to produce sound involved vibrations of their swim bladder – a gas-filled organ used to control buoyancy – driven by rhythmic contractions of specialised “drumming” muscles, the paper said.

However, the sound production mechanism of the pulses generated by Danionella cerebrum, which has the smallest known brain of any vertebrate, had been a mystery as swim bladder-related muscle mechanisms did not provide a plausible explanation for the origin of the sound.

The scientists at Charité University in Berlin have found the fish has a unique sound production system, involving a drumming cartilage, specialised rib and fatigue-resistant muscle. This allows the fish to accelerate the drumming cartilage at extreme forces and generate rapid, loud pulses.

“Understanding this extraordinary adaptation expands our knowledge of animal motion and highlights the remarkable diversity of propulsion mechanisms across species, contributing to our broader understanding of evolutionary biology and biomechanics,” the paper said.

The team of scientists used high-speed video recordings to investigate the mechanism of sound production.

To produce sound, a rib that lies next to the swim bladder is moved by a special muscle into a piece of cartilage. When the rib is released it hits the swim bladder and makes the drumming sound. The rib is much harder in males, which explains why females do not produce sounds.

The scientists have not established why the fish make such loud sounds but suggested it could help navigate murky waters or be an aggressive tactic used by males to warn off competition.

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