In the streams of central and southern Myanmar, there exists a peculiar tiny fish about the size of a grain of rice. They are known as the miniature brain danio (Danionella cerebrum), which are transparent creatures measuring about 12 millimeters in length and considered to be one of the smallest known vertebrates today. Uniquely, though small in size, the sounds they produce are surprisingly loud, and under certain conditions, their sound levels can reach a piercing 140 decibels.
Scientists explain this phenomenon as a fascinating love song—the courtship behavior of the miniature brain danio. During the mating season, male fish can produce these firecracker-like loud sounds, which are exceedingly rare in nature due to their volume. Research published by marine biologist Clara Amorim (Clara Amorim) of the University of Lisbon in Portugal and other researchers show that this “song” actually correlates with the health status of the male fish and that female fish tend to choose males who sing longer as mating partners.
Amorim and her colleagues found that the “most talkative” fish in groups of various sizes could lay more eggs. This loud “courtship song” not only possibly conveys information about the male fish’s health but also, in some species of fish, the song can accelerate the maturation of the female fish’s eggs and promote spawning.
Even more astonishing is how the miniature brain danio can produce such a huge sound. According to Verity Cook (Verity Cook), it is due to the male fish rapidly contracting muscles to cause a small piece of cartilage inside the body to swiftly knock against the swim bladder, a mechanism similar to beating a drum that creates the “boom.”
Moreover, the special body shape and characteristics of the miniature brain danio make it of great scientific value. These fish remain transparent throughout their lives, with the top of their skull never closing, as if naturally born for scientific research. With the help of gene editing and fluorescent protein technology, researchers can directly observe the activity of living neurons, providing a valuable research model for neuroscience. By studying the miniature brain danio’s “courtship song,” scientists can more detailedly map the neural pathways in the vertebrate brain that generate and process sound signals.
The brain of this tiny but powerful miniature brain danio is the smallest in all living vertebrates, its volume comparable to a poppy seed, yet it hides the loudest secret in the silent ocean.
But Cook warns not to underestimate it. “Even small fish with small brains can have complex and interesting behaviors,” says Cook, “and love.”
