Human activities such as eutrophication and pollution are increasing the frequency and intensity of aquatic hypoxia (low dissolved oxygen) worldwide. Recent studies have demonstrated that hypoxia can impair reproduction in fish; however, studies to date have focused on short term exposures in species that do not experience hypoxia in their natural environment. In this thesis, I investigated the effect of hypoxia on sex hormone levels in the African mouth-brooding cichlid, Pseudocrenilabrus multicolor victoriae. In Chapter one, I validated a non-invasive holding water technique of hormone measurement for use with P. multicolor. In Chapter two, I applied this technique to investigate the effect of hypoxia on sex hormones in female P. multicolor sampled across the reproductive cycle in a long-term laboratory acclimation to hypoxia, and at the time of capture in a field survey of populations exposed to life-long hypoxia. Results from Chapter one demonstrate that repeated use of the holding water technique is not detectably stressful to P. multicolor, and that holding water measures of testosterone and estradiol provide a biologically robust and reliable index of plasma hormone levels. Results from Chapter two demonstrate that hypoxia does not affect sex hormone levels in P. multicolor exposed to low versus high dissolved oxygen conditions in the lab. Comparisons of field populations of P. multicolor from two high and two low dissolved oxygen sites indicated higher testosterone levels, a higher testosterone/estradiol ratio, and a lower percentage of brooding females in P. multicolor captured from the low dissolved oxygen field sites. Taken together, these results suggest that chronic or lifelong exposure to hypoxia may provide compensatory mechanisms, and that fishes may exhibit a threshold response when dealing with the energetic demands of hypoxia.