The effects of temperature on ovarian aromatase (cyp19a1a) expression and sex differentiation in summer flounder (Paralichthys dentatus)

Female summer flounder grow considerably faster and larger than males, and a tremendous increase in performance can therefore be realized through production of monosex female populations. Rearing temperature has been shown to affect sex differentiation in other teleost species by influencing expression of genes encoding transcription factors or enzymes involved in endocrine function. Cyp19a1a is a well-studied gene that had been shown to play a role in ovarian development, and exhibits sexually dimorphic expression in other species. In the present study, summer flounder (37 days post-hatch; DPH) were raised at 13, 16 or 19 °C. Fish from all three treatments were sampled throughout development and analyzed in qPCR to determine cyp19a1a gene expression levels. Sex ratios of additional fish grown to ≥150 mm at each temperature treatment were determined. Low female production was achieved overall (26.9, 17.6 and 0 % at 13, 16 and 19 °C, respectively). Cyp19a1a expression was significantly lower at 52 DPH (~15 mm total length) at the male-producing temperature (19 °C) and increased to similar levels as other treatments at 66 DPH. Expression levels later in juvenile development (66–191 DPH) largely decreased with fish size. The period of sex differentiation in summer flounder remains unknown, but cyp19a1a expression patterns suggest that it may occur earlier in development than that of congenerics. Further research is necessary to understand the sex-determining mechanisms in this species before sexually dimorphic growth can be used to achieve economic advantages in commercial production.