DIFFERENCES IN AGE AND SEXUAL MATURATION BETWEEN PREMIGRANT AND MIGRANT SILVER EELS IN THE LOWER RIVER RHINE SYSTEM

摘要

Every year in autumn (Sept-Nov) the majority of large female yellow eels experience drastic physiological and morphological changes and become silver eels. These changes are associated with the onset of sexual maturation (Pankhurst, 1982; Aroua et al., 2005) and are accompanied by cessation of feeding and the start of migration. Swimming itself was found to stimulate enlargement of the eyes that indicates progressing maturation, oocyte growth and fat deposition (Palstra et al., 2007), increased LH content in the pituitary and plasma 17beta-estradiol levels (E2; van Ginneken et al., 2007).