Imagine a fish smaller than your fingernail, yet capable of generating a sound as loud as a gunshot. Meet the Danionella cerebrum, a fish found in the streams of Myanmar. Despite measuring a mere 12mm, the male of this species boasts a sound-producing capability that rivals industrial machinery.
Described in a recent study published in PNAS, this challenges our understanding of how fish generate sound. Traditionally, fish utilize a mechanism involving the rhythmic contraction of specialized muscles on their swim bladder (a gas-filled organ for buoyancy control) to produce vibrations. However, the D. cerebrum, known for having the smallest brain of any vertebrate, presented a puzzle. The swim bladder-based mechanism simply couldn't explain the extraordinary sound production observed.
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Scientists from Charité University in Berlin discovered a unique sound production system in this tiny fish. Instead of relying on swim bladder vibrations, the D. cerebrum utilizes a specialized drumming apparatus comprising three key elements:
1. Drumming Cartilage: This hard piece acts as the "hammer" in the system.
2. Specialized Rib: This acts as a lever, propelling the drumming cartilage forward.
3. Fatigue-Resistant Muscle: This powerful muscle contracts rapidly, generating the force needed for the sound production.
This unique setup allows the D. cerebrum to accelerate the drumming cartilage at incredible forces, exceeding 2,000 times the force of gravity. Upon release, the cartilage strikes the swim bladder, generating a rapid and loud pulse. Interestingly, unlike males, females lack the hardened rib, explaining their inability to produce sound.
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While the reason behind these loud sounds remains unclear, scientists speculate they might serve multiple purposes. They could help the fish navigate murky waters by emitting ultrasonic signals for improved spatial awareness. These sounds might also act as an aggressive tactic, employed by males to deter competition.
