[Hormonal stimulation, in vivo, of the ovary of European eel in the yellow stage].

The immature ovary of yellow eel was stimulated by a long-term treatment with a gonadotropin II rich extract of carp pituitary. Ovarian follicles of treated yellow eels showed an accumulation of lipidic vacuoles in the oocyte cytoplasm and a thickened follicular envelope (in this regard, they resembled the ovarian follicles of previously studied silver eels). The treatment also resulted in a significant but limited increase in the gonadosomatic ratio and mean follicle size (these values were much lower than those measured in silver eels). No change in pigmentation or general morphology was observed. Thus, under our experimental conditions, a gonadotropic stimulation of the yellow eel leads to some but not the totality of the ovarian modifications which occur physiologically during silvering.