Temperature modulates gonadal development and sex ratio of pirancanjuba Brycon orbignyanus

In this study, we assessed the effect of temperature on gonadal development and sex ratio in Brycon orbignyanus. The fish were kept at three different temperatures (20 °C, 23 °C, and 26 °C) from the beginning of exogenous feeding. At 420 days after fertilization, 10 individuals were collected per temperature regimen for histological and hormonal evaluation of the gonads. The results showed that the sexual pattern was temperature-dependent. All individuals maintained at 20 °C were undifferentiated, with only somatic cells in their gonads. At 23 °C, most individuals were immature males (7/9, 77.8%), and at 26 °C, the majority were males still in maturation process (6/9, 66.7%) and males with gonads in the regression phase were also found. In the hormonal assay, the only treatment in which the individuals had detectable estradiol levels was 23 °C. Testosterone levels were quantified from individuals in the three treatments. We conclude that continuous treatment at 23 °C and 26 °C favors testicular development in B. orbignyanus, and gonadal development is accelerated in fish farmed at 26 °C, as the males in the latter treatment matured at one year and two months of age.