In tilapia, all-male populations are beneficial for farmers because males have a faster growth-rate than females and it avoids the constraints associated with reproduction. Considering that a male grows 1.6-fold more than a female after 7 months of culture and that tilapia annual production is 2.8 million tons (2nd World Fish production), there is a substantial economical gain for producers. All-males are commonly produced by androgen treatment to masculinise XX larvae. Search for alternatives based on more consumer and environment-friendly methods represents a major challenge for aquaculture. Both genetic or temperature sex control are good alternatives but require long progeny testings to sex & identify fish. Furthermore, selection of breeders (YY males & XX female) giving 95-100% males is necessary. A reliable and precocious sexing procedure would accelerate progeny testings, finding of particular genotypes and reduce production costs for farmers. It will also help scientists in developing temperature and genetic approaches for sex control. The Cirad-INTREPID Unit proposes in the SexTil (Sexing Tilapia) project to: 1) Construct an easy sexing kit for Nile tilapia to be used in laboratories by analysing precociously the expression of a Male-gene. 2) Develop a simpler sexing kit to be used by tilapia farmers consisting on the protein coding the Male-gene. 3) Validate these 2 types of kits on important Nile tilapia strains (Bouake; Manzala; GIFT ..) and on the other farmed tilapia species. 4) Perform a marketing exploration study to analyse the potential of these sexing kits worldwide, and thus help a French company (ie start-up) to commercialize the kits worldwide. Thus it will have considerable economical repercussions, reducing feeding costs, the necessary rearing space, labour and time requirements as well as promote environmentally-friendly sex control alternatives to hormones.