The ribbon eel changes its color and sex as it matures in the wild.

Nature · Published 3 October 2026 Swipe more like this →

In short: This striking creature undergoes a dramatic transformation throughout its life, shifting from jet black as a juvenile to vibrant blue or yellow as an adult. Beyond its shifting appearance, the ribbon eel is a protandric hermaphrodite, meaning it transitions from male to female as it reaches full maturity.

The ribbon eel, Rhinomuraena quaesita, is a unique moray eel found across the Indo-Pacific, from East Africa to southern Japan. It is the sole member of its genus, distinguished by a highly unusual urogenital system where sex cells move anteriorly rather than toward the tail. With up to 255 vertebrae, it is remarkably thin and elongated, often spotted by divers with its head poking out of sand or coral rubble. While once thought to be two separate species based on color—blue for R. quaesita and black for R. amboinensis—scientists now recognize these as a single species undergoing developmental color shifts.

Developmental changes in the ribbon eel are tied to its life cycle. Juveniles are black with yellow dorsal fins, while adult males display striking blue and yellow markings. Females, which grow significantly larger at up to 130 cm, are primarily yellow. This color-coded sex change is unique among moray eels. Curiously, these eels are colorblind, possessing only one type of photoreceptor, suggesting that their vivid hues do not serve a primary function in mating. In the wild, they can live up to twenty years, though they are notoriously difficult to keep in captivity, where they often refuse to eat.

Despite their widespread distribution, these eels face environmental pressures. As a species that prefers shallow waters between 1 and 57 meters, they are particularly vulnerable to habitat degradation, such as coral bleaching and pollution. While currently listed as least concerned by the IUCN, researchers warn that the loss of reef structure and overfishing could threaten their ability to find prey and reproduce. Unlike their wild counterparts, captive ribbon eels do not exhibit the same color-maturity correlations, and most fail to survive beyond a year, highlighting the complexity of their natural biological requirements.

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