In European sea bass a combination of genetic and environmental factors are involved in sexual differentiation. Under aquaculture conditions the males are the predominant sex (more than 75% of fish) but for aquaculture the interest is to obtain all-females stocks because they grow about 30% more than males. It has been shown that temperature can influence the proportion of sex ratios by modifying the process of sex differentiation during which the gonads are very sensitive to exogenous factors. Studies performed with undifferentiated fish prove that constant high (19-21°C) as well as low (15-16°C) temperatures during all the developmental stages promote male-dominant populations (>90%). On the other hand, low temperatures from fertilization untilthe middle of metamorphosis (100 days aprox.) result in the highest female proportions that can be achieved only with temperature manipulation (72-74%) (Pavlidis et al 2000). With the aim to refining treatment protocols as well as to understand the process involved in ovarian and testicular differentiation, experiments with different temperature regimes were carried out.
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