Fluorescence of European glass eel (Anguilla anguilla L.) under ultraviolet light

The existence of ultraviolet (UV) biofluorescence in nature has been documented in a wide range of flora and fauna. Biofluorescence is utilised throughout biological and ecological functionality, and although invisible to the human visual perception, this spectral range is known to be integral for communication across flocks, swarms, shoals and between individuals. Under UV illumination, European eel juveniles (glass eel) were found to fluoresce bright yellow. Follow‐up experiments using the UV light source on preceding eel life stages such as pigmented glass eels (elvers), ‘bootlace eels’ (juvenile yellow eels), older yellow eels and migrating silver eels, all found that these stages had lost the capacity for biofluorescence. The information gathered from this study suggests that the use of UV light for presence/absence glass eel arrival surveying could be a useful and effective tool for researchers in the research field.