Date of Award

Fall 2015

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

David L Berlinsky

Second Advisor

William H Howell

Third Advisor

Timothy S Breton


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, hormones or enzymes involved in endocrine function such as cyp19a1a, foxl2, dmrt1 and amh. These genes have been linked to female (cyp19a1a, foxl2) or male (dmrt1, amh) development, and exhibit sexually dimorphic expression in some species. In the present study, summer flounder (37 days post hatch; DPH) were raised at 13°C, 16°C or 19°C. Fish from all three treatments were sampled during early development (38-66 DPH), and fish from 13 and 16°C treatments were sampled through later juvenile development (191 DPH). A partial summer flounder cDNA sequence for cyp19a1a was identified, verified, and submitted to the NCBI GenBank database. Partial summer flounder sequences were also were identified for foxl2, dmrt1 and amh, but these single sequence reads were not verified or submitted to NCBI. Summer flounder samples were analyzed in qPCR to determine cyp19a1a, foxl2, dmrt1 and amh 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. Cyp19a1a expression levels later in juvenile development (66-191 DPH) largely decreased with fish size. No clear trend in gene expression levels was present for foxl2, dmrt1 or amh. 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, and that cyp19a1a may be a more robust sex marker in summer flounder than foxl2, dmrt1 or amh. 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.