LUCKENBACH, J/Adam; EARLY, Lea/W; BORSKI, Russell/J; ROWE, Ashlee/A; GODWIN, John; North Carolina State Univ., Raleigh: Aromatase: a functional biomarker for female differentiation in a teleost fish

The Southern flounder (Paralichthys lethostigma) is a high-value teleost fish in which females grow faster and reach a larger adult body size than males. We have shown that Southern flounder exhibit a plasticity of sex determination where water temperature may influence phenotypic sex during early development. The unusual mode of sex determination and interest in commercial production warrants better understanding the mechanisms and timing of sex determination in Southern flounder. P450 aromatase is responsible for conversion of androgens to estrogens in vertebrates. Therefore, higher expression of aromatase would be expected in ovarian tissue when compared to testes. Through cloning and sequencing of the cyp19-gene encoding aromatase and TaqMan� based, quantitative RT-PCR (qRT-PCR) we aim to develop a functional biomarker for early detection of female differentiation in Southern flounder. Sequence comparisons of aromatase intron regions from fish caught in both NC and TX waters revealed a substantial inter-individual variation that may be related to differences in sex determination responses. Through qRT-PCR, we found that adult ovarian tissue showed high expression of aromatase, while it was undetectable in testes. Liver, intestine, kidney, muscle, and brain showed little or no expression of this aromatase in adults, whereas high expression was detected in the spleen. Gonads sampled from juvenile fish undergoing sexual development are under analysis to precisely define the body size at which sex determination occurs. More generally, this should provide a powerful tool to rapidly define conditions for controlling sex determination in this species and better understand environmental influences on sex determination in fishes.