Abstract
The European sea bass (Dicentrarchus labrax) is a major species for Mediterranean aquaculture, with more than 160 000 tons produced yearly. It has a haploid genome size of 675 Mb, distributed in 24 chromosome pairs, without sex chromosomes. The sex ratio of wild populations is mildly, but significantly, biased towards females. However, under the farming environment, sex ratios are highly male‐biased. This, along with the fact that males grow about 30% slower than females and mature earlier, has prompted interest in the control of its sex ratio and the elucidation of its sex determining mechanism.European sea bass is a gonochoristic species with polygenic sex determination (>3 sex ratio associated QTLs), in which the contribution of genetics and the environment to sex ratio variance is approximately equal. However, the identity of the sex determining factor(s) remains unknown. There is a strong influence of the parental genotypes on the offspring sex ratio, which can vary from < 10% to ≈ 90% females. The heritability estimate of sex tendency is high (h 2 = 0.62). Sex determination is thought to occur when fish are 3–4 cm in length, and sex related growth is apparent early, before the morphological sex differentiation of the gonads takes place. Temperatures higher than 17 °C during the thermosensitive period (0–60 days post‐fertilization) have a masculinizing effect. Manipulating growth through feeding during the sex differentiation period does not alter sex ratios. Combining selective breeding and environmental control is expected to lead to the production of female‐biased populations with superior growth.