Real-time PCR-based prediction of gonad phenotype in medaka

An important endpoint in aquatic bioassays for potential endocrine disrupting chemicals (EDCs) is the gonadal phenotype of exposed fish, with special interest in intersex and sex-reversed individuals. Traditionally, the assessment of gonad phenotype is done via histology, which involves specialized and time-consuming techniques. The method detailed here increases the efficiency of the analysis by first determining the relative expression of four genes involved in gonad development/maintenance in Japanese medaka (Oryzias latipes), and then by using principal component analysis, assigning a phenotype to each gonad based upon the gene expression data. The gonad phenotype and the sexual genotype, which can be determined in medaka, can then be compared to assess potential adverse effects of exposure to endocrine disrupting chemicals.