Endocrine changes during the annual reproductive cycle of the red porgy, Pagrus pagrus (Teleostei, Sparidae)

Abstract

Changes in 17β-estradiol (E2), estrone (E1), testosterone (T), 11-ketotestosterone (11KT), and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) levels were correlated to changes in gonadosomatic index (GSI), vitellogenin concentration (Vg), ovarian and testicular histology during the annual reproductive cycle of the red porgy, Pagrus pagrus. The production of E2, E1, T and 17,20β-P was confirmed by analysis of the steroidogenic activity of ovaries. In females, the average concentration of E2 was lower than 2 ng ml−1. E2 values first increased significantly at the stage of endogenous vitellogenesis and remained high during exogenous vitellogenesis. E1 levels were lower values than E2 (less than 300 pg ml−1), but they increased at the beginning of exogenous vitellogenesis. Estrogens concentrations followed similar pattern to Vg and were significantly correlated. Mean levels of T were mostly lower than 1 ng ml−1. They followed a pattern similar to that of E2 except for a further increase observed at the stage of final maturation. T and E2 levels were significantly correlated. The concentration of 11KT did not change significantly. The levels of 17,20β-P ranged between 0.22 and 1.22 ng ml−1 but changes were not related to gametogenesis. In males, the concentrations of T and 11KT fluctuated significantly during the sexual maturity stages, showing a similar pattern and were significantly correlated to GSI changes. T levels increased during spermiogenesis and spermiation stages to reach about 3 ng ml−1. 11KT levels stayed about half those of T. The levels of estrogens showed no significant changes. Level of 17,20β-P showed no significant variation related to male maturity. Results are discussed in relation to changes in plasma steroid levels during gametogenesis of other multiple spawner species.