Genetic sex manipulation of Nile Tilapia: The alternative method for production of a high percentage of male seeds in a hatchery scale by YY-female technology

Abstract

The Nile Tilapia, Oreochromis niloticus, is worldwide-cultured fish species for their fast growth. However the production of this species has long been hindered by precious maturity of female. Recently YY-male technology has been introduced for producing all male seeds depend on sex determination mechanism, XX-female; XY-male, of this species (Scott et al., 1989; Mair et al., 1997; Tuan, et al., 1998). In this study, we compared the reproductive ability of YY-male and YY-female and suggest the alternative method for production of a high percentage of male seeds in hatchery scale by YY-female technology.The gametes produced from YY-male with XX-female crosses showed significantly lower hatching rates than that of XX-female with XY-male crosses. Otherwise, hatching and survival rates in early developmental stage (up to swim-up stage) of gametes produced from YY-female with both XY-male and XX-male crosses presented similar with that of XX-female with XY-male crosses. Due to the low fecundity of YY-males in experiment I, we decided that YY-female technology would be more reliable to produce all male seeds in hatchery scale. In experiment II, mass produced progenies from tanks stocked YY-females and XX-males showed 93.5% (S.D. 6.4%) of male. YY-female presented relatively lower spawning frequency than that of normal females, but not differ in amount of seed produced and mean spawning interval. We concluded that YY-female technology with improved seed production methodology (Noh et al., 1997) enables the production of a high percentage of male seeds in hatchery scale.