Sex determination and the feasibility of genetically male tilapia production in the Thai-Chitralada strain of Oreochromis niloticus (L.)

This paper presents the findings from investigations on sex determination and attempts to produce monosex male tilapia through the use of novel YY-males in the Thai-Chitralada strain of Oreochromis niloticus cultured commercially in Thailand. To determine the underlying variability in sex ratio, 95 progeny groups, derived from single pair matings of normal broodstock, were sexed over a period of 2 years. In addition, diallel-type crosses were generated from seven females and five males. Of the 7822 progeny sexed, there were 3951 males (50.5%), with the overall sex ratio being not significantly different from 1:1 ( P>0.25). However, progeny sex ratios ranged widely from 15.5% to 100% male. The data were highly heterogeneous ( P