Seasonal steroids variations and maturity stages in the female chub, Leuciscus cephalus L. (Pisces, Cyprinidae).

Biometric evaluation, ovary histomorphometry, plasma l7/i-estradiol (E2) and androgens (A) concentrations were investigated through the gonadal maturation and spawning of the wild chwb, Leuciscus cephalus. A lower concentration of plasma E2 was recorded from January (oogonia) to March (previtellogenic oocytes), while estradiol concentrations increased in April, when the ovary mostly contained vitellogenic oocytes. In July, when it was prevalently composed of postovulatory follicles, there was a decline in E2 plasma concentrations. Low concentrations of this steroid remained in the plasma until January, while high concentrations of androgens reached a peak in February and April preceding and following E2. The observed seasonal changes in plasma steroids, reflecting the pattern of follicles size development, were to a large extent consistent with observations made in other cyprinids. Since they define the reproductive cycle of the European female chub, they will be useful in the construction of a maturity schedule for wild populations.