| Abstract
| - Hypoxia is affecting thousands of square kilometers ofwater and has caused declines in fish populations and majorchanges in aquatic communities worldwide. For the firsttime, we report that hypoxia can affect sex differentiationand sex development of zebrafish (Danio rerio), leadingto a male-biased population in the F1 generation (74.4% ±1.7% males in the hypoxic groups versus 61.9% ± 1.6%males in the normoxic groups, n = 5; p < 0.05, χ2 test). Theincrease in males was associated with downregulationsof various genes controlling the synthesis of sex hormones(i.e., 3β-HSD, CYP11A, CYP19A, and CYP19B) as well asan increase in the testosterone/estradiol ratio. The male-dominated populations caused by hypoxia will have reducedreproductive success, thereby threatening the sustainabilityof natural fish populations.
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