What is the young of an eel called?

An elver is a young eel.

The eel is a long, thin bony fish of the order Anguilliformes. It is any of more than 800 species of teleost fishes characterized by elongate wormlike bodies. Anguilliforms include the common freshwater eels as well as the voracious marine morays.

Eels occur to considerable depths in most oceans and are greatly diverse in tropical seas. They range in colour from drab gray or black in deep-sea species to colourful and patterned in tropical reef species. Only the freshwater eels (family Anguillidae), which are in places abundant and greatly valued as food, are of major economic importance.

The annual invasion of fresh waters by Anguilla elvers is a locally well-known process; it occurs during October–March in Europe and in spring in other temperate regions.