ABSTRACT
The glass eel is the stage of arrival of juvenile eels from the sea (Fig. 1). The name refers to the transparency of the small eels which are virtually colourless upon arrival in freshwater apart from some pigmentation around the top of the cranium and the tip of the tail. With residence in freshwater, glass eels become increasingly pigmented and undergo marked changes in their behaviour. Historically the term “elver” has been used to describe this stage of freshwater recruitment (e.g., Schmidt 1925; Ege 1939; Deelder 1958), but the term “glass eel” is now almost universally used to avoid confusion with small eels that have been resident in freshwater for varying periods. A recent review (Fukuda et al. 2013), and also the ICES standard terminology (ICES 2014) concluded that the term ‘glass eel’ should be used to describe juvenile eels until the dorsolateral pigmentation across the top of the body is complete; this stage also corresponds to the commencement of feeding and growth.
