Growth, sex differentiation and gonad and plasma levels of sex steroids in male‐ and female‐dominant populations of Dicentrarchus labrax obtained through repeated size grading

Abstract

Starting from 66 days post hatching (dph), European sea bass Dicentrarchus labrax were graded successively to create a fast growing (L‐extreme) and a slow growing (S‐extreme) population. The L‐extreme population grew significantly larger (ANOVA, n = 89–101, P v . 66·7 ± 0·9 g, mean ± s . e .). When the two populations were sexed, the L‐extreme consisted of 96·5% and the S‐extreme of 30·2% females, while the ungraded control had 59·2% females. Sex differentiation began first in females at a total length ( L T ) 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 (E 2 ) was significantly higher in the female‐dominant population at the onset of ovarian differentiation (ANOVA, n = 10, P P n = 10, P P n = 10, P 2 is closely related with ovarian differentiation and the onset of oogenesis, while T and 11‐KT is more related to spermatogenesis and precocious maturation.

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