MORPHOLOGICAL VARIATION IN AN EARLY DEVELOPMENTAL STAGE (GLASS EEL) OF EUROPEAN EEL (ANGUILLA ANGUILLA)

摘要

The life cycle of the European eel has been a complete mystery until the 20th century, when Johannes Schmidt discovered that the Sargasso Sea was the spawning location for Anguilla species (Van Ginneken et al, 2005). With his research the central mystery of the life cycle was elucidated, but there still remains a lack of knowledge on many aspects of the early life history of the European eel, Anguilla anguilla. One of those aspects is the occurrence of broad- and narrow headed phenotypes in this species. The different head shapes have been related to different diets, where broad-headed eels would feed on larger and harder prey (Proman & Reynolds, 2000). Although some research has been focusing on this dimorphism, very little is still known about howand when this dimorphism arises and what parts of the body plan are involved. To find out when this dimorphism arises we examined a sample of glass eels, using biometric and morphometric analyses, as well as morphological studies. The glass eel stage (stage V) is the first stage at which the eels have a more typical eel shape and migrate into fresh waters. With this study we aim to characterize whether the onset towards divergent shape- and morphological variation (broad- vs narrowheaded phenotypes) isalready apparent at the glass eel stage.