Study of the sexual maturity of female bluefin tuna: purification and partial characterization of vitellogenin and its use in an enzyme-linked immunosorbent assay

Plasma steroid levels of female bluefin tuna (BFT) Thunnus thynnus rose fro m c. 1.5 ng ml(-1) during the quiescent period (March) to c 7 ng ml(-1) dur ing the ripening period (May). Testosterone (T) increased further to c. 8 n g ml(-1) during the pre-spawning period (June) while 17 beta -oestradiol (E -2) began to decrease. In the post-spawning period (August) steroid levels decreased to <1 ng ml(-1). Vitellogenin (Vtg) plasma levels seemed to follo w changes in E-2, showing an increase from the quiescent period to the ripe ning period of c. 18 mg ml(-1) decreasing slightly before spawning, and the n decreasing after spawning. The Vtg content in plasma showed a good correl ation both with the plasma levels of E-2 and T and with the percentage of v itellogenic oocytes at different periods of the reproductive cycle. Thus th e ELISA could be taken as validated. Immunohistochemical staining of ovarie s with anti BFT-Vtg serum demonstrated a high cross-reactivity with yolk pr oteins allowing the identification of vitellogenic oocytes. (C) 2001 The Fi sheries Society of the British Isles.