elver

An elver is a young eel. Eels are slender, elongated, and usually scaleless fish found in all seas and freshwater bodies.12

Catadromous fish, like eels, spend most of their lives in freshwater and then migrate to the sea to breed. The best-known examples are the European eel (Anguilla anguilla) and the North American eel (A. rostrata), which spawn in the Sargasso Sea. Their transparent, leaf-like larvae, called leptocephali, drift on currents to continental shelves. After about two and a half years, they transform into elvers, which are bottom-dwelling and pigmented. These elvers, also known as glass eels, migrate upstream into freshwater streams in the spring, often in massive numbers. They grow into yellow eels, remaining in freshwater for 5 to 20 years before maturing into silver eels and returning to the sea to spawn, after which they die.34