Sex-ratio, early sex steroid profiles and cyp19a1b, dmrt1 and foxl2 gene expressions upon high temperature treatment of undifferentiated African catfish juveniles (Clarias gariepinus)

Different mechanisms are involved in high temperature-induced masculinization among teleost fishes. These mechanisms need to be investigated in African catfish, a species with a XX/XY genetic sex determinism that can be overridden by high temperature (HT). The influence of HT on the three main sex steroid hormones (testosterone – T, 17β-estradiol – E2, and 11-ketotestosterone – 11KT) was assessed from non-fertilized eggs to 14  days post-hatching (dph) in eggs or whole body of six full-sib progenies reared at 28 °C (control) and 36 °C for 6 to 8 dph (high masculinizing temperature). HT effect on foxl2, cyp19a1b and dmrt1 expression was also investigated in the head at the end of the thermal treatment (8 dph) and shortly after (14 dph) in the six progenies. Masculinization rates in fish exposed to HT ranged from 30 to 100%, but did not influence sex steroid levels. However, the masculinization rate was correlated with 11KT levels at 1-h post-fertilization, suggesting that 11KT level at this phase may influence the masculinization potential. Expression of foxl2 was not detected in the head during the experimental period while, to our knowledge, this is the first report of dmrt1 expression in teleost fish head (perhaps in brain). Similar to sex steroid hormones, HT did not induce significant changes in cyp19a1b or dmrt1 relative expressions in the brain. Nevertheless, when results were split into two groups, according to the masculinization rates of progenies, lower thermosensitive progenies showed high cyp19a1b relative expression shortly after HT treatment, while in control groups, highly thermosensitive progenies displayed high dmrt1 relative expression at 14 dph. While this may be true, a direct link between the HT treatment and the biological indicators analyzed was not clear and the mechanisms of masculinization have to be further investigated, particularly in the gonad.