Sex-associated DNA markers from turbot

The genomes of male and female turbot, Psetta maxima (Linnaeus, 1758), were screened for sex-specific sequences by comparative random amplified polymorphic DNA (RAPD) assays performed on pooled samples. As turbot females grow much faster than males, there is an increasing interest in differentiating between the sexes, and such markers would enable the sexing of individuals even at early stages of development. Four sex-associated DNA markers, with molecular sexing efficiencies ranging from 77 to 90%, were identified and further characterized. Two markers were identified from pooled female samples, one from pooled male samples (both sets collected from the wild), whereas a fourth marker was found in the female pool of farm-bred siblings. Parallel application of the three markers isolated from wild-caught individuals yielded a combined molecular sexing efficiency of 90% in males and 83.3% in females. While the three markers isolated from the wild should be useful to predict the sex in natural turbot populations, the fourth marker showed sex-association limited only to the family where it was isolated from. Nonetheless, it can be used for molecular sexing of brooders originating from the target family and potentially their offspring as well. The application of such molecular sex markers with limited scope is a potential strategy in aquaculture for those species for which no universal sex marker is available.