Danionella cerebrum, a translucent fish species of only 12 mm length, produces high amplitude sounds exceeding 140 dB (re. 1 µPa, at a distance of one body length) — comparable to a jet engine during take-off in 100 m distance.
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Danionella cerebrum has a pair of extrinsic, indirect sonic muscles that house the drumming cartilage. When a sonic muscle contracts, the fifth rib is pulled anteriorly and builds tension as it pulls the cartilage. The sudden release of the cartilage causes it to rapidly strike the swim bladder, producing a short, loud pulse. A burst of pulses is generated with either bilaterally alternating or unilateral muscle contractions. In sum, this mechanism enables loud and stereotyped sounds that can be elicited in structured sequences, making it a unique solution for acoustic communication and ultrafast skeletal motion in vertebrates surpassing the limitation of muscle contraction speed. Image credit: Ralf Britz, Senckenberg Natural History Collections.
“The snapping shrimp can generate a popping sound of up to 250 dB with its claws,” said Dr. Ralf Britz, an ichthyologist at the Senckenberg Natural History Collections.
“The mating calls of the flightless kakapo reach 130 dB, and elephants can produce noise of up to 125 dB with their trunks.
“Fishes, on the other hand, are generally considered to be rather quiet members of the animal kingdom.”
“However, there are certain fish species that can be surprisingly loud. For example, the male plainfin midshipman fish attracts its females with an audible vibrato of around 100 Hz and 130 dB.”
In the new study, Dr. Britz and his colleagues examined Danionella cerebrum, a miniature teleost fish with the smallest known vertebrate brain.
“This tiny fish can produce sounds of over 140 dB at a distance of 10 to 12 mm — this is comparable to the noise a human perceives of an airplane during take-off at a distance of 100 m and quite unusual for an animal of such diminutive size,” Dr. Britz said.
“We tried to understand how the fish manages this and what mechanisms are responsible for this achievement.”
Using a combination of high-speed video, micro-computed tomography, gene expression analysis, and finite difference methods, the researchers found that Danionella cerebrum males possess a unique sound-generating apparatus that includes drumming cartilage, a specialized rib, and a fatigue-resistant muscle.
“This apparatus accelerates the drumming cartilage with a force of over 2,000g and shoots it against the swim bladder to produce a rapid, loud pulse,” Dr. Britz said.
“These pulses are strung together to produce calls with either bilaterally alternating or unilateral muscle contractions.”
Due to its small size and lifelong optical transparency, Danionella cerebrum is an emerging model organism in biomedical research.
The species is native to shallow and turbid waters of Myanmar.
“We assume that the competition between the males in this visually restrictive environment contributed to the development of the special mechanism for acoustic communication,” Dr. Britz said.
The study’s results challenge the conventional notion that the speed of skeletal movement in vertebrates is limited by muscle movement.
“Understanding the extraordinary adaptation of Danionella cerebrum expands our knowledge of animal locomotion and highlights the remarkable diversity of propulsion mechanisms in different species,” the authors said.
“This contributes to a broader understanding of evolutionary biology and biomechanics.”
“The sounds produced by other Danionella species have not yet been studied in detail; it would be interesting to learn how their mechanism of sound production differs and how these differences relate to evolutionary adaptation.”
“In combination with its lifelong transparency, the genus Danionella offers a unique opportunity to compare the neural mechanisms underlying the sound generation between the different species.”
The study was published in the Proceedings of the National Academy of Sciences.
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Verity A.N.O. Cook et al. 2024. Ultrafast sound production mechanism in one of the smallest vertebrates. PNAS 121 (10): e2314017121; doi: 10.1073/pnas.2314017121
