May thermic preferendum induce sex reversal of sexually undifferentiated juveniles African catfish, Clarias gariepinus (Burchell, 1822) ?

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Résumé

High temperatures, under experimental conditions, induces masculinisation in many fish species and particularly in Nile tilapia, Oreochromis niloticus. Despite many studies on the temperature sex determination (TSD) process in this species, only few information are available on TSD under natural conditions. The aim of our study was to determine if sexually undifferentiated juvenile tilapia voluntary migrate to high temperature that could induce masculinisation. Eight days post-fertilization XX juveniles (2 families, n = 150) were reared during 30 days in a thermic continuum constituted of 3 aquaria (50l) at 28, 32 and 36.5°C connected together by a channel. Two other aquaria were used as normal control (28°C) and sex reversed control (36,5°C 30 days) used to assess the thermosensitivity of each family. We observed that up to 66% of juveniles from the family 1 preferentially moved to high temperature (36.5°C) during the period of gonad differentiction (from 10-28 dpf). These juveniles displayed a significant sex reversal (28.4%) as well as control reared at 36.5°C (82.7%). On contrary, the majority (90%) of the juveniles from the family 2 move only to 32°C (optimal temperature for growth). No inversion was observed in this family and sex reversal in the control at 36.5°C was only 26.4%. Our results could suggested that, depending of the thermosensitivity of the family, undifferentiated juveniles voluntary migrated towards high temperature (36.5°C) that induced sex reversal. These results bring new insights in the sex determination process and open new way of consideration to explain the biological importance of TSD in Nile tilapia.

Mots-clés

sex reversal, Clarias gariepinus, African catfish, temperature-dependent sex determination, sexual differentiation