This paper reports a study on the progeny sex-ratio distribution in the Florida red tilapia. This hybrid originated as a cross between O. mossambicus male and O. urolepis hornorum female, which was then crossed with O. niloticus and O. aureus in order to improve its growth rate and its resistance to low temperature. We have studied the sex-ratio of 111 progenies from 46 females and 12 males, where the male percentage varied between 5% to 89%. The analysis of distribution showed three groups characterised by a mean male percentage of 26.7 ± 9.8; 50.0 ± 8.9 and 70.3 ± 5.5%. The stability of sex ratios in repeated single pair matings and the parental influence on progeny sex ratios obtained are in agreement with a polygenic basis of sex determination in this complex hybrid. © 2005 Elsevier B.V. All rights reserved.