Thermosensitivity of the sex differentiation process in the African catfish, Clarias gariepinus: Determination of the thermosensitive period

• Exposure to high temperature between hatching and 23 days post-hatching has a masculinizing effect in Clarias gariepinus.
• The most thermosensitive period of sex differentiation is limited to 6-8 days post-hatching, preceding the first events of histological differentiation.
• Thermosensitivity of the sex differentiation process varies among families.

Gonadal sex differentiation in gonochoristic fish is generally labile and under the control of two interacting processes: genetic sex determination (GSD) and environmental sex determination (ESD). Numerous experimental studies deal with temperature induced-sex differentiation in teleosts, but none focused on the African catfish Clarias gariepinus. The aim of this study was to confirm the thermosensitivity of the sex differentiation process and to determine the thermosensitive period during the African catfish development. Fish were exposed to high temperature (36 °C) for 3 days at different periods during ontogenesis. The treatment was applied every 3 days from fertilization until 29 days post-hatching (dph). Before and after the thermal treatment, fish were reared at 28 °C. Gonadal development was histologically characterized on fish sampled at 10, 15, 20, 25, 35, 45, 55 and 70 dph. Our results demonstrated that the African catfish displays a thermosensitivity of the sex differentiation process, with a masculinizing effect of high temperature (36 °C). The most thermosensitive period extended from 6 to 8 dph. Fish batches exposed to 36 °C during this period showed a sex-ratio skewed towards the male phenotype, ranging from 58 to 100% (high inter-familial variability). The African catfish gonads (male and female) stayed histologically undifferentiated until 20 dph. Obvious signs of gonadal differentiation clearly appeared at 25 dph in females and at 45 dph in males.Variability in sex-ratios between progenies and in the response to thermal treatment suggests a role of minor genetic factors and interactions between genomic and environmental determinants in the expression of the sexual phenotype.Statement of relevance1.This paper provides novel methods to control African catfish Clarias gariepinus sex differentiation through high temperature exposure and then to produce all-male populations.2.Our work underlines the possibility to significantly reduce high temperature (masculinizing effect) treatment period to 3 days and consequently increase survival rate of progenies after treatment.3.This study also shows the inter-family variability of thermosensitivity on the sex differentiation process in Clarias gariepinus.