Inheritance of sex in two ZZ pseudofemale lines of tilapia Oreochromis aureus

Abstract

This paper reports a study on the sex determination system of the blue tilapia, Oreochromis aureus. Investigations were carried out using a pseudofemale line in two populations of O. aureus, known as Egyptian Population (EP) and Israel Population (IP). In O. aureus, males are the homogametic sex (ZZ/ZW), and sex reversal of fry with estradiol results in the production of some functional sexreversed fish with a female phenotype and ZZ male genotype, known as pseudofemales or D-females. Crosses between ZZ pseudofemales and ZZ males theoretically should provide monosex ZZ male progeny only. We have studied the sex ratios of progeny from 43 IP (F 2 to F 3 generations) and 51 EP (F 1 to F 5 generations), pair-matings between normal males and pseudofemales. In IP, the male percentage in progenies ranged between 83% to 100% in F 2 and 66% to 100% in F 3 . In EP, male percentage was more constant, varying from 88% to 100% in F 1 , from 96% to 100% in F 3 and from 97% to 100% in F 5 . In EP, F 2 and F 4 pseudofemales produced only monosex male progeny. This apparent difference in sex ratio frequency distributions between the two O. aureus pseudofemale lines could be due to the selection of males. EP pseudofemales were mated with their siblings for F 2 and F 3 pseudofemales or with closely related males for F 4 and F 5 pseudofemales. Conversely, IP pseudofemales were crossed with nonrelated males originating from research center broodstock, resulting in a higher proportion of females in sex ratio of progenies from successive generations of pseudofemales. The role of inbreeding is discussed in the context of predominantly monofactorial sex chromosome determination system operating in this species, influenced by other factors (genetic and environmental). The present study also shows that it is possible to fix the male sex determining factors

Two unlinked loci controlling the sex of blue tilapia (Oreochromis aureus)

“…This study, as well as those of Hopkins (1979) and Mélard (1995), demonstrated male homogamety for this species. A monofactorial sex determination system with two sex chromosomes (WZ) in O. aureus was also supported by results from the analysis of progeny sex ratios from pseudofemales (Desprez et al, 2003), who showed that it is possible to obtain high proportions of male progeny from successive generations of pseudofemales by hormonal sex reversal and progeny testing.…”

Study of sex ratio in progeny of a complex Oreochromis hybrid, the Florida red tilapia

“…The hypothesis of a differential mortality of certain genotypes, suggested by Jalabert et al (1971) and Chen (1969), cannot be excluded. Moreover, as demonstrated by Shirak et al (2002) in an inbred Table 4 Number and percentage of crosses giving each sex-ratio (h : U) in theory of Avtalion and Hammerman (1978) (Mair et al, 1997;Desprez et al, 2003a). These recent studies have demonstrated that male genetic sex determining factors (sex chromosomes, autosomal factors) can be fixed in a line of breeders.…”

“…To explain unpredicted results in Oreochromis, which are not consistent with a monofactorial sex chromosomes model, a more complex system was proposed by adding a further genetic sex determining/regulating locus, the autosomal recessive gene (F,f) to the major bsex chromosomesQ (Wohlfarth and Wedekind, 1991;Mair et al, 1991a,b;Trombka and Avtalion, 1993;Desprez et al, 2003a). Crossingover and recombination of sex determining genes could also account for these unpredicted sex-ratios (Mair et al, 1991a,b;Mü ller-Belecke and Hö rstgenSchwark, 1995).…”

“…Observation of significant deviations from predicted sex ratios suggests the influence of additional factor(s) (environmental or genetic) other than sex chromosomes on the sex determination in this genus (Avtalion and Hammerman, 1978;Majumdar and McAndrew, 1983;Mair et al, 1991a,b;Wohl-farth and Wedekind, 1991;Baroiller and D'Cotta, 2001;Desprez et al, 2003a). The main interest in the model of sex determination in tilapia is motivated by the practical and commercial implications in the production of monosex male populations for aquaculture.…”

“…The main interest in the model of sex determination in tilapia is motivated by the practical and commercial implications in the production of monosex male populations for aquaculture. Monosex male populations, usually preferred to optimise the production system (males grow faster than females; decreased reproduction; reduction of sexual/ territorial behaviour; achievement of higher average growth rate), are generally produced on a large scale by hormonal sex inversion or by genetic approaches (interspecific hybridisation; YY super male or ZZ pseudofemale technology, respectively in O. niloticus and O. aureus) (Guerrero and Guerrero, 1988;Wohlfarth, 1994;Mair et al, 1997;Desprez et al, 2003a).…”