One of the primary challenges in European seabass farming is optimizing the number of females, which grow faster and mature later than males. However, typical rearing practices often result in populations with a high proportion of males. To test whether photoperiod, temperature and fasting impact the sex ratio, two distinct experiments were conducted. In the first one, we tested the effects of two photoperiods (12 L:12D vs 10 L:14D), applied until 90 dph at 16 °C. Then, on the same fish, photoperiod was set to 12D:12 L and four different temperature treatments (19 °C, 21 °C, 23 °C, and 25 °C) were applied from 90 to 160–192 dph. In a second experiment, we tested the impact of fasting at four different times during the sex determination window: from 60 to 65 dph; 81 to 87 dph; 102 to 110 dph and 123 to 133 dph, at a temperature of 21 °C. Neither photoperiod (in the first experiment) nor starvation during larval development (in the second experiment) altered sex ratio. Conversely, we revealed (in the first experiment) that the proportion of females increased with post-larval rearing temperature: 30.4% at 19 °C, 36.3% at 21 °C, 44.1% at 23 °C, and 48.7% at 25 °C. Thus, late warm thermal treatments, following an initial cold treatment at 16 °C until 90 dph, can be useful to compensate the deficit of females in farmed sea bass production.