Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was long a mystery. Of particular interest has been the search for the spawning grounds for the various species of eels, and identifying the population impacts of different stages of the life cycle.
Distribution and size of leptocephali larvae of the American eel, Anguilla rostrata
Leptocephalus larva of an ocean eel
Glass eels at the transition between ocean and fresh water; the skin is still transparent and the red gills and the heart are visible; length about 8 cm
Juvenile eels, length about 25 cm
Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.
Eel
The European conger is the heaviest of all eels.
Eel eggs hatch firstly into the leptocephalus larval stage.
Larval eels become glass eels as they transition from the ocean to fresh water.
