2 research outputs found
Growth, sex differentiation and gonad and plasma levels of sex steroids in maleâ and femaleâdominant populations of Dicentrarchus labrax obtained through repeated size grading
19 pages, 6 figures, 1 table.-- Printed version published Apr 2005.Starting from 66 days post hatching (dph), European sea bass Dicentrarchus labrax were graded successively to create a fast growing (Lâextreme) and a slow growing (Sâextreme) population. The Lâextreme population grew significantly larger (ANOVA, n = 89â101, P < 0·01) attaining twice the wet mass of the Sâextreme population at 300 dph (130·9 ± 1·8 v. 66·7 ± 0·9 g, mean ± s.e.). When the two populations were sexed, the Lâextreme consisted of 96·5% and the Sâextreme of 30·2% females, while the ungraded control had 59·2% females. Sex differentiation began first in females at a total length (LT) of 97 ± 4 mm and wet mass of 9·4 ± 1·2 g (150 dph), and was completed when fish reached 166 ± 6 mm and 53·4 ± 6·4 g (250 dph) in both sexes. Precocious maturation in males was positively correlated to growth. Gonad oestradiol (E2) was significantly higher in the femaleâdominant population at the onset of ovarian differentiation (ANOVA, n = 10, P < 0·05) and in the plasma after the appearance of the first primary oocytes (P < 0·01). Gonad testosterone (T) increased in both populations after sex differentiation (ANOVA, n = 10, P < 0·05), while plasma levels were significantly higher in the maleâdominant population (P < 0·001). Both gonad and plasma 11âketo testosterone (11âKT) were significantly higher in the maleâdominant population (ANOVA, n = 10, P < 0·01) reaching maximal values at spermiation. The results suggest that E2 is closely related with ovarian differentiation and the onset of oogenesis, while T and 11âKT is more related to spermatogenesis and precocious maturation.This work was undertaken as part of the research programme âImproving production efficiency of sea bass farming by developing methodologies to eliminate environmental androgenesisâ, and was supported by a research grant from the European Community to S.Z., C.C.M. and F.P. under the Quality of Life and Management of Living Resources programme (contract Q5RS-2000-31365).Peer reviewe