Male-specific DNA markers from African catfish (Clarias gariepinus)

We searched for sex-specific DNA sequences in the male and female genomes o f African catfish, Clarias gariepinus (Burchell, 1822) by comparative rando m amplified polymorphic DNA (RAPD) assays performed on pooled DNA samples. Two sex-linked RAPD markers were identified from the male DNA pool and conf irmed on individual samples, showing good agreement with phenotypic sex. Bo th markers were isolated, cloned and characterized. The first marker (CgaY1 ) was nearly 2.6 kb long, while the length of second one (CgaY2) was 458 bp . Southern blot analysis with a CgaY1 probe showed strong hybridizing fragm ents only in males and not in females under stringent conditions, indicatin g the presence of multiple copies of CgaY1 in the male genome. When tested by zoo blot on the genomes of two closely related species from the Clariida e family, CgaY1 hybridized to the DNA of Heterobranchus longifilis and gene rated a faint male-specific band at low stringency. CgaY2 produced similar hybridization pattern in both sexes of C. gariepinus, C. macrocephalus and H. longifilis. Specific primers were designed to the sequences and the mark ers were amplified in multiplex PCR reactions together with a control band common to all individuals. This allowed for rapid, molecular sexing of the species on the basis of a simple three band (male) versus one band (female) pattern. According to our knowledge these are the first sex-specific DNA m arkers isolated from a siluroid fish species.