Analyse comparative, physiologique et moléculaire des effets de trois traitements masculinisants chez le tilapia du Nil, Oreochromis niloticus, et recherche de marqueurs de traçabilité liés à ces approches

摘要

Due to the genuine advantages of this species (fast growth, spontaneous breeding in captivity), the aquaculture production of tilapias, and especially of the Nile tilapia Oreochromis niloticus (L.), has been growing steadily over the past 30 years. Nevertheless, the success of this production is largely dependent on the sex control efficiency, in order to take advantage of the better growth of males and to avoid uncontrolled breeding that can cause crowding and dwarfism. The use of male monosex populations has thus become a standard in tilapia aquaculture since the 1970s. The dietary administration of 17α-methyltestosterone (17MT) is still the major masculinising procedure used in tilapia farming nowadays. However, it raises issues concerning the environment, fish farmers and consumers'health. More recently, alternatives to hormonal sex reversal have been evaluated, i.e. the use of YY males, treatment using aromatase inhibitors or elevated temperatures during the early life stages. In the present study, the effects of fadrozole (an aromatase inhibitor), elevated temperatures and 17MT have been compared on the survival and growth of XX fish, and as regards to the expression patterns in the brain and gonads of key genes implicated in fish sex differentiation. Comparisons seen in these induced-males were performed with genetic XX females and XY males. The growth rates of fish raised at elevated temperature were similar to those of genetic males, thereby emphasizing the relevance of this method as an alternative to hormonal sex reversal of Nile tilapia, when using highly thermosensitive strains. Whether the growth of tilapia is stimulated by androgens or depressed by estrogens is discussed. The analysis of expression profiles of the genes involved in sexual differentiation reveals different patterns in the brain and in the gonads. Amh and cyp19a1b are strongly stimulated in the brain of XX neomales treated by elevated temperatures. Conversely, amh is inhibited in the brain of fish treated with fadrozole, suggesting that amh is directed or indirectly regulated by aromatase. In the gonads of XX neomales, the levels of dmrt1 and amh are much higher than in genetic XY males. Further studies should analyse a) the fertility of neomales, b) the plasmatic levels of steroids and proteins, c) the histology and immunohistochemistry of the brain and the gonads, and d) the expression of other genes.Keywords : Nile tilapia / Masculinisation / Temperature / Hormones / Growth / Genes