Sex control and sex determinism study in Eurasian perch, Perca fluviatilis, by use of hormonally sex-reversed male breeders

Abstract

The Eurasian perch, Perca fluviatilis, displays sexual growth dimorphism in which females grow significantly faster than males. In this species, the sex-determining mechanism is not yet described. In order to control sex by steroid treatment and to study the genetic sex-determining mechanism in Eurasian perch, the first step is to optimize sex reversal using steroids. A combination of three hormonal doses (40, 60 and 80 mg of 17α-methyltestosterone kg −1 diet), four initial body weights (43, 71, 150 and 205 mg) and two treatment durations (30 and 80 days) was tested in duplicate. Complete masculinisation (100% male progenies) occurred when the treatment was applied in fish initially ranging from 40 to 71 mg body weight. Treatment applied at a larger body weight (150 and 205 mg body weight) provided variable proportions of males with two testes (45–62%), females (0–29%), XX males with a single twisted testis (16–40%), fish with ovotestis (0–18%) and sterile fish (0–27%). The sperm of XX males, determined on the basis of gonad morphology (single twisted testis), was used to fertilize eggs. The resulting offspring displayed sex ratios ranging between 95% and 100% females, while the sex ratio of most XY male progenies did not differ significantly ( P>0.05) from a 50:50 balanced sex ratio. These results suggest that a female homogamety (XX)–male heterogamety (XY) chromosomal system is primarily operating in Eurasian perch. Nevertheless, because some males arise from crosses with XX males, and because two populations resulting from normal crosses display a sex ratio significantly ( P<0.05) deviated towards males (60.7%) or females (65%), this suggests the action of other genetic sex-determining factors (autosomal or polygenic).