Meeting Abstract

65.5  Tuesday, Jan. 6  Hypoxia alters gonadal androgen synthesis in the estuarine fish Fundulus grandis CHEEK, A.O.; Houston Baptist Univ. acheek@hbu.edu

Estuarine and coastal hypoxic zones are increasing in frequency, duration, and area worldwide. The sub-lethal impacts of prolonged hypoxia on fish are predicted to include loss of habitat, suppressed growth, and impaired reproduction. In salt marshes, hypoxia develops and dissipates in tandem with diel cycles of photosynthesis and respiration, particularly during summer. At marsh sites with moderate (2.5 mg/L dissolved oxygen) to severe (0.93 mg/L DO) diel hypoxia, wild Fundulus grandis(Gulf killifish) have smaller ovaries and testes, lower sex steroid hormone concentrations, and are more likely to be reproductively regressed than killifish at sites without diel hypoxia. In order to investigate potential mechanisms by which hypoxia reduces sex steroid concentrations, androgen production was measured in testis explants incubated under normoxia or hypoxia. Hypoxia dramatically reduced 11KT production, but had no effect on testosterone production when progesterone was supplied as a precursor. With 11β-hydroxytestosterone (11βOHT) supplied as precursor, hypoxia did not change 11KT production, suggesting that hypoxia specifically inhibits 11β-hydroxylase (CYP11B1), the enzyme that converts T to 11βOHT. Inhibition of the terminal steps of gondal steroidogenesis is consistent with the observation that circulating T concentration was unaffected by diel hypoxia in wild fish, but 11KT concentration was significantly reduced. In F. grandis, diel hypoxia appears to alter specific steps in gonadal steroid production, rather than centrally inhibiting the reproductive axis.