PRODUCTION OF A HIGH PERCENTAGE OF MALE OFFSPRING WITH 17-ALPHA-ETHYNYLESTRADIOL SEX-REVERSED OREOCHROMIS-AUREUS .2. COMPARATIVE REPRODUCTIVE-BIOLOGY OF FEMALES AND F2 PSEUDOFEMALES AND LARGE-SCALE PRODUCTION OF MALE PROGENY

In Oreochromis aureus, the use of pseudofemale spawners (sex-reversed male with a female phenotype) is an alternative technique for producin g monosex genetically male tilapia offspring. This study compared the reproductive capacities of F2 pseudofemales and females and evaluated the possibilities of applying this process of high percentage of male production on a large scale in earthen ponds, The percentage of non-sp awning pseudofemales F2 (40%) is high in comparison to females (20%), On average females spawned three times and pseudofemales spawned once and significant variation was observed in the frequency of spawning (P < 0.1),The pseudofemales presented typical gonads and relative fecund ity similar (P > 0.05) to that of females; (respectively 1668 +/- 1445 and 1643 +/- 1070 eggs.kg(-1) per spawning). The GSI of spawning fema les and pseudofemales was respectively 3.7 +/- 1.7% and 4.4 +/- 2.2% ( P > 0,05). The sex ratio of progeny of pseudofemales deviated signific antly (P < 0.01) in favour of males (90.7 to 91.0%) compared to the re sults observed with normal females (52.0 to 57.0%). The male percentag e obtained could result from polyfactorial sex determination in 0, aur eus. The mean fry production with pseudofemales per m(2).day(-1) was 3 5% lower (10.0) with the pseudofemales than with the normal females (1 5.4). This process gives less satisfactory results in comparison with classical techniques, but it does provide a sufficient fry production rate and male percentage, especially in intensive culture.