Glass eels are the juvenile stage of eel species, particularly the European eel and American eel. They are named for their transparent bodies, which help them evade predators in their early life. Glass eels typically migrate from the ocean to freshwater rivers and estuaries, where they will grow into adult eels. During their migration, glass eels undergo a transformation, gradually developing pigmentation as they mature into elvers. This stage is crucial for their survival, as they adapt to life in freshwater environments. Glass eels play an important role in aquatic ecosystems and are also sought after in commercial fisheries.