Elevated temperature applied during gonadal transformation leads to male bias in zebrafish (Danio rerio)

Temperature effects on sex determination or differentiation exist in many fish species, with high temperatures predominantly producing more males. The present study aimed at elucidating the genetic background of temperature effects on sex differentiation in zebrafish. Experimental fish were generated by matings between 4 or 6 golden females and a normal or a mitotic gynogenetic male, respectively. All the larvae were reared at 28.5°C until they were divided into 3 groups per full-sib family, a control group raised at 28.5°C and 2 treatment groups reared at 35°C from 20 to 30 dpf or 25 to 35 dpf, respectively. Backcross progenies, reared at 28.5°C, were derived from F1 temperature-treated sons (35°C, 25-35 dpf) that were sired by a mitotic gynogenetic male and their corresponding mothers. No significant differences were observed regarding the survival rate between the control and treatment groups. Significant differences in the phenotypic male proportions from the controls were observed in groups treated at 35°C. The sex ratio in zebrafish was influenced by the male spawner, the female spawner, and a significant interaction of genotype by temperature. Backcross experiments point to a continuum of major genetic, minor genetic, and environmental factors in the expression of the phenotypic sex in zebrafish.