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 ¼ 89-101, P < 0Á01) attaining twice the wet mass of the S-extreme population at 300 dph (130Á9 AE 1Á8 v. 66Á7 AE 0Á9 g, mean S.E.). When the two populations were sexed, the L-extreme consisted of 96Á5% and the Sextreme of 30Á2% females, while the ungraded control had 59Á2% females. Sex differentiation began first in females at a total length (L T ) of 97 AE 4 mm and wet mass of 9Á4 AE 1Á2 g (150 dph), and was completed when fish reached 166 AE 6 mm and 53Á4 AE 6Á4 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 ¼ 10, P < 0Á05) and in the plasma after the appearance of the first primary oocytes (P < 0Á01). Gonad testosterone (T) increased in both populations after sex differentiation (ANOVA, n ¼ 10, P < 0Á05), while plasma levels were significantly higher in the male-dominant population (P < 0Á001). Both gonad and plasma 11-keto testosterone (11-KT) were significantly higher in the male-dominant population (ANOVA, n ¼ 10, P < 0Á01) reaching maximal values at spermiation. The results suggest that E 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. # 2005 The Fisheries Society of the British Isles

Body size dimorphism of sea-reared Atlantic salmon (Salmo salar L.): Implications for the management of sexual maturation and harvest quality

“…Sex-ratio is an important population parameter and is likely to be skewed following weight-grading in sexually dimorphic populations. This was shown in sea bass (Papadaki et al, 2005) and in this study by the power of BW to discriminate between genders in association with the seasonality in sex-ratio observed at harvest. Significant dimorphism most probably occurs at the time of weight-grading leading to a higher proportion of males in the best performing cohorts harvested earlier in the season.…”

“…In this later species, repetitive weight-grading of mixed-sex population allowed segregating a fast-growing, 96.5% female, population for experimental purpose (Papadaki et al, 2005). Mechanical segregation of genders and sex-specific harvest could minimize maturation during sea bass ongrowing to optimize biomass output and facilitate the production of various market size.…”

Gonadotropins in European sea bass: Endocrine roles and biotechnological applications

“…The expression of lhcgr increased at 250 days in male gonads, while no significant differences were found during the period analyzed in females. The increase in Lh content and lhb/lhcgr expression could be related to the significant number of precocious males that appeared in this population (Papadaki et al, 2005;Felip, Zanuy, Gómez, unpublished).…”

Updating control of puberty in male European sea bass: A holistic approach

“…At 250 dpf, gonad differentiation has been completed in both sexes (Papadaki et al, 2005). After fertilization, and generally under intensive culture conditions, as much as 20-30% of the male population can attain anticipated puberty or precocity (Begtashi et al, 2004); in this case, gonad size does not exceed 1.5% of the GSI.…”