Artificial fertilisation of cultured Senegalese sole ( Solea senegalensis ): Effects of the time of day of hormonal treatment on inducing ovulation

To develop a protocol for the hormonal induction of ovulation and artificial fertilisation in Senegalese sole, it is necessary to determine whether the time of day of the GnRHa injection influences the lapsed time to ovulation or the egg quality. Hormonal treatments were administered at 06:00, 12:00 and 19:00h. The time of ovulation was 42.5±0.6h following hormonal treatment, and there were no significant differences between groups. However, it was noted that the time of ovulation was the most homogeneous in Groups 6 and 12, and most females in these groups ovulated at 41 or 44h following hormonal treatment. Fertilisation rates were lower in fish injected at 19:00h than in those injected at 06:00 or 12:00h, and the largest number of larvae per kg of each female was obtained when the treatment was administered at 06:00. These results suggest that hormonal treatments should be applied in the early morning to promote the maximum number of good quality eggs.