leptocephali

Leptocephali are the larval forms of eels (order Anguilliformes). The term leptocephalus comes from Greek roots meaning “slender head.” These larvae are typically transparent and leaf- or ribbon-shaped, and they spend a substantial portion of their early life in the open ocean.

Morphology and development are distinctive. Leptocephali have elongated, flattened bodies with a veil-like, gelatinous skin, lack true scales, and possess a continuous dorsal and anal fin that runs along much of the body. They usually have a small head and mouth, and their digestive system is reduced or operates differently from that of later life stages. Their appearance changes as they metamorphose into later stages such as glass eels.

Life cycle and ecology. Eels begin life as leptocephali after spawning in the pelagic ocean. Depending on species, leptocephali may drift for weeks to years before beginning metamorphosis into the next life stage, typically called glass eels, then elvers, as they migrate into coastal waters and estuaries. From there, they mature into the adult eels that inhabit freshwater or coastal environments. Classical views associate many European and American eel species with spawning in distant open-ocean areas, such as the Sargasso Sea, before their larvae migrate toward continental areas.

Distribution and significance. Leptocephali are found in the world’s oceans, reflecting the broad geographic ranges of their eel hosts. They are a key focus of ichthyoplankton studies and fisheries science, aiding understanding of eel population dynamics, migration, and life history. Taxonomically, the term applies to the larval stage across multiple eel families, including freshwater eels (Anguillidae) and conger eels (Congridae).

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