Genetic and temperature sex determination in the turbot Scophthalmus maximus

Genetic (GSD) and temperature sex determination (TSD) have been investigated in the turbot, Scophthalmus maximus using sex inversed males (androgen treated males=ATM) and females (oestradiol treated female-s= OTF). ATM and OTF have been produced through feeding treatments using 17[alpha]-methyltestosterone and 17[bêta]-oestradiol at a dosage of 3 or 5 mg/kg food starting from 35 days post fertilization (dpf) during periods of 500 or 700° days. 16 ATM and 6 OTF were mated with normal females or males. The 22 resulting progenies and 11 control families were reared at 17°C. For TSD evaluation, parts of 8 of these 33 families (2 from ATM and 6 from controls) have been reared at 15°C, 17°C or 24°C from 35 dpf to 100 dpf. Then all progenies (GSD and TSD) have been reared at 17°C until 11 months old (100 g body weight) for the sex ratio assessment. For 27 progenies reared at 17°C, sex ratios perfectly fit in with the hypothesis of a male homogamety ZZ/ZW system (X-square test; P<0.01). However, 2 ATM, 2 OTF and 2 control progenies presented skewed sex ratios with an excess of males (65-80%). Finally, 24 C treatments significantly affected 3 out of the 8 progenies evaluated for TSD in decreasing the rate of males. It is concluded that in turbot sex is mainly determined by a pair of sex chromosome with a female heterogamety (ZZ/ZW) but sex ratios may also be modulated by parental factors, high temperature and possible temperature/genotype interactions. This project was partly supported by France Turbot and the EU in the PL 97-3796 FAIR Project. (Résumé d'auteur