leptocephalus

The leptocephalus is the transparent, leaf-shaped larval stage of certain marine ray-finned fish, most notably eels and tarpons. These larvae are characterized by their flattened, ribbon-like bodies and their small heads. Unlike the larvae of many other fish, leptocephali possess a gelatinous, transparent body devoid of the typical segmented musculature seen in adults. Their digestive system is also underdeveloped, suggesting they absorb nutrients directly from the water.

Leptocephali are found in the open ocean and are pelagic, meaning they drift with ocean currents. Their duration in this larval stage can vary significantly, ranging from months to several years, depending on the species. During this time, they feed on dissolved organic matter in the water column. As they grow, they gradually develop adult features.

The transformation from leptocephalus to a juvenile fish is a dramatic metamorphosis. The body becomes more muscular and opaque, and the characteristic fins of the adult fish begin to form. This transition marks the end of their pelagic life and often precedes a migration to coastal or freshwater environments, depending on the species' habitat. The study of leptocephali is crucial for understanding the life cycles and distribution of many commercially important fish species, particularly the Anguilliformes (true eels).