Molecular marker-assisted sex control in half-smooth tongue sole (Cynoglossus semilaevis)

Half-smooth tongue sole females grow larger and faster than males. An all-female population would be of significant benefit for tongue sole aquaculture. In the present study, a female-specific AFLP marker (CseF305) was isolated from female genomic DNA of the tongue sole and sequenced. One pair of SCAR primers was designed based on the sequences of the female-specific marker. A PCR method for identifying genetic sex of the sole was developed. PCR amplification of genomic DNA from tongue sole adults using the SCAR primers resulted in a specific fragment in 30 female individuals, but not in 30 males. Secondly, effects of methyltestosterone treatment on the female:male sex ratio of tongue sole fry were examined. Methyltestosterone at a concentration of 20–100 μg/L·H2O can induce genetic females to reverse to phenotypic males in juvenile tongue sole and produce a high proportion of males (97–100% males). Phenotypic males with female genotype, that is, neo-males, were detected by using female-specific SCAR primers. The neo-males were cultured and matured, and used to mate with normal females to produce progeny. 130,000 fry were produced by using sperm from neo-males. Genetic sex identification demonstrated that 73% of the neo-male progeny fry contained female-specific DNA markers. Three combinations of sex chromosomes (ZZ, ZW and WW) were observed in the neo-male progeny. WW super-female individuals containing 2 huge heteromorphic chromosomes were found in some fry.