Role Involvement of Gonadal Steroidsand temperature in the During Natural and Temperature-Induced Sex Differentiation of the Tilapia Oreochromis niloticus

J.F Baroiller1,2, H. D´Cotta1,2, A. Toguyeni3, F. Clota1 and A. Fostier2

1: CIRAD-EMVT / Unité de Recherche Aquaculture, c/o Cemagref, 361 rue J.F. Breton, BP

5095, 34033 Montpellier-Cedex 1 (FRANCE)

2: INRA / Station Commune de Recherches en Ichtyophysiologie, Biodiversité et

Environnement (SCRIBE), Campus de Beaulieu, 35042 Rennes-Cedex (FRANCE)

3: Institut du Développement Rural / Université Polytechnique de Bobo-Dioulasso, 01 BP 1091 Bobo-Dioulasso 01 (BURKINA FASO)

ABSTRACT

Populations composed exclusively of males are extremely useful in the commercial production of tilapias. They take into advantage the high growth-rate of males and avoid the rapid over-population of rearing facilities brought about by the efficient reproduction of females. This aquaculture requirement hasfavoured encouraged research on sex determinism and differentiation of the tilapia group. In the case of Oreochromis niloticus reared at 27ºC, the sex differentiation of the female gonad can be detected histologically at 28 days post-fertilisation (DPF) by the appearance of the first meiosis features. In vitro The analysis of the gonadal steroidogenesis has put into evidence a sex specificity of the steroidogenic potentialities associated to sex. Hence, estrogens are essentially synthesised in ovaries while 11-oxygenated androgens are produced in testis. Experiments on hHormonal treatments promoting sex-inversion have shown that 11-hydroxy-androstenodione androstenedione is the most potent masculinising hormone among the androgens identified, with while estradiolbeing is the most potent feminising hormone. These treatments are mostly efficient if when applied before 15 DPF. Thus, wWe measured the gonadal endogenous levels of estradiol and androgens in the gonads at this critical period and during sex differentiation. In addition, expression studies were performed of genes coding for two key enzymes involved in the synthesis of these steroids (11hydroxylase for 11hydroxy-androstenodione androstenedione and aromatase for estradiol) were performed. The aromatase gene is strongly expressed during female differentiation, in correlated correlation to with the determination of high estradiol levels in the ovaries, whereas,whereassuch gene expression and levels of hormone levels of both are lower in the developing males testes. On the other hand, the eExpression of the 11hydroxylase gene is weak and does not appear to be sex-specific. Furthermore, masculinising classic progenies orgenetic all-females by treatment with high temperatures populations, we. We also studied aromatase and 11hydroxylase expressions in the gonads of genetic all-female and all-male populations reared either at the standard (27ºC) and or at a masculinising temperatures (35ºC) during sex differentiation. Gonadal expression of 11hydroxylase was low and was not modified in genetic females when masculinised by a high temperature exposure. In contrast, aromatase expression was strongly repressed in these fishes with masculinisation. The potential role of both androgens and estrogens is discussed during normal natural and or temperature induced sex differentiation is discussed.

[Evidemment si tu avais le temps de donner quelques chiffres: niveaux hormones, expression relative des gènes…ce serait bien. Mais le temps, le temps…]