Influence du génotype sexuel sur les caractéristiques de la reproduction de femelles (génotype WZ) et de pseudofemelles (génotype ZZ) chez le tilapia Oreochromis aureusInfluence of sexual genotype on reproductive traits of females (genotype WZ) and pseudofemales (genotype ZZ) in the tilapia Oreochromis aureus

The sex reversal of Oreochromis aureus (male genotype: ZZ ; female genotype: WZ) with an oestrogen (17α-ethynylestradiol) treatment produces pseudofemales with a male genotype (ZZ). Crossing these fish with normal males (ZZ) gives, in theory, 100 % male offspring. We have determined and compared the principal traits of reproductive biology of three broodstock batches of O. aureus. First batch (batch 1) was constituted using normal females only, the second (batch 2) involved pseudofemales only, while the third batch (batch 3) contained both females and pseudofemales. Fecundity and mean egg weight was not significantly different in females and pseudofemales. In the third group, spawning rate of the pseudofemales (0.6 spawns) was lower than that of the females (6.4 spawning). In this last group, 60 % of the pseudofemales never reproduced. In batches 1 and 2, there were no differences between females (6.9 spawns) and pseudofemales (4.7 spawns). Lowest spawning rate of pseudofemales may result from the expression of the male sexual genotype of these fish.