Publication Abstract

Seasonal variations and maturity stage related differences in serum levels of sex steroids, vitellogenin and thyroid hormones in common dentex (Dentex dentex)

Seasonal variations and maturity stage related differences in serum levels of sex steroids, vitellogenin and thyroid hormones in common dentex (Dentex dentex)

M. Pavlidis, L. Greenwood, B. Mourot, C. Kokkari, F. Le Menn, P. Divanach and A.P. Scott

Seasonal variations in serum concentrations of 17-estradiol (E₂), vitellogenin (Vg), testosterone (T), 11 ketotestosterone (11-KT), and thyroid hormones (T₄, -thyroxine; and T₃, 3,5,3'-triiodo--thyronine) were investigated during the first, second, and third reproductive cycles in intensively reared populations of common dentex, Dentex dentex, and correlated with gonadal development and spawning. In females, there were baseline E₂ values (<0.10 ng/ml) and negligible Vg concentrations during the postspawning and pregametogenesis period (June to December), and these increased thereafter to peak during the spawning period. Maximum T₃ and T₄ serum concentrations were found around spawning. There was a positive correlation during vitellogenesis and final maturation between Vg and T₃ (r² = 0.366). In addition, Vg and T₃ concentrations were statistically higher in the stages of vitellogenesis and final maturation than at the other stages (P < 0.001). Minimum T₃ and T₄ concentrations (October) coincided with the decrease in water temperature and the associated decrease in the daily feeding rate and the specific growth rate. In males, as in females, seasonal changes in serum levels of T and 11-KT were well correlated with gonadal development. The presence of males in the stage of completed spermiogenesis in December coincided with the surge in both androgens and this increase lasted until the end of the spawning period. There were no significant differences in serum T₃ and T₄ levels among the maturity stages. The observed seasonal changes in serum gonadal steroids and Vg reflected the pattern of oocyte development and the spawning behavior of common dentex and were typical of the patterns described in most multiple spawners studied to date. Thyroid hormones may enhance early ovarian development and stimulate vitellogenesis in female dentex.

Reference:

M. Pavlidis, L. Greenwood, B. Mourot, C. Kokkari, F. Le Menn, P. Divanach and A.P. Scott, 2000. Seasonal variations and maturity stage related differences in serum levels of sex steroids, vitellogenin and thyroid hormones in common dentex (Dentex dentex). General and Comparative Endocrinology, 118: 14-25.

M. Pavlidis, L. Greenwood*, B. Mourot, C. Kokkari, F. Le Menn, P. Divanach and A.P. Scott*

General and Comparative Endocrinology, 118: 14-25