Eels undergo several transformations in their early stages. What are commonly called “baby eels” are distinct developmental phases, each with a unique appearance. These young creatures begin their lives in oceanic depths, embarking on extensive migrations that shape their changing forms. Understanding these appearances reveals the adaptations that allow eels to thrive across diverse aquatic environments.
The Flat, Leaf-Like Larva
The earliest larval stage of an eel is known as a leptocephalus, a name meaning “slim head.” This form is strikingly different from an adult eel, characterized by its flat, ribbon-like, or leaf-shaped body. The leptocephalus is transparent due to its laterally compressed body, jelly-like substance, and absence of red blood cells. Its internal organs are small, and it possesses a simple, tube-like gut.
These larvae typically measure between 5 to 10 centimeters in length, though some species can reach up to 30 centimeters. They drift passively in the open ocean, carried by strong currents like the Gulf Stream, which aids their long-distance dispersal from spawning grounds. Leptocephali have small, pointed heads and temporary fang-like teeth, present until metamorphosis.
The See-Through “Glass” Stage
Following the leptocephalus stage, eels undergo metamorphosis into a glass eel. During this transition, their previously flat, leaf-like bodies become more rounded and cylindrical, resembling a miniature adult eel. Glass eels largely retain their transparency.
Their clear bodies allow internal structures to be visible. Glass eels typically measure around 5.5 to 7.0 centimeters in length, with American eels often being about 2 inches long. At this stage, they begin their migration from the open ocean towards continental shelves, estuaries, and coastal waters, driven by instincts to find suitable habitats.
The Mini-Eel Appearance
The elver stage develops as the glass eel progresses into coastal and freshwater environments. This stage marks a shift in appearance as elvers begin to develop pigmentation, losing their transparency. Their bodies gradually acquire a grayish, brownish, or greenish opaque coloration.
Elvers are miniature versions of adult eels, possessing the characteristic elongated, snake-like body. They typically measure a few inches long, though some can grow up to 12 inches. This development of pigmentation provides camouflage as they continue their journey upstream into freshwater rivers and streams.