Aquatic hypoxia is a teratogen and affects fish embryonic development

Hypoxia occurs over large areas in aquatic systems worldwide, and there is growing concern that hypoxia may affect aquatic animals, leading to population decline and changes in community by elimination of sensitive species. For the first time, we report that sublethal levels of hypoxia can significantly increase (+77.4%) malformation in fish embryonic development. Disruption of apoptotic pattern was clearly evident at 24 h post-fertilization, which may be a major cause of malformation. Furthermore, embryonic development was delayed, and balance of sex hormones (testosterone and estradiol) was disturbed during embryonic stages, implicating that subsequent sexual development may also be affected. Overall, our results imply that hypoxia may have a teratogenic effect on fish and delay fish embryonic development, which may subsequently impair species fitness leading to natural population decline.link_to_subscribed_fulltex

Hypoxia affects sex differentiation and development leading to a male-dominated population in zebrafish (Danio rerio)

Hypoxia is affecting thousands of square kilometers of water and has caused declines in fish populations and major changes in aquatic communities worldwide. For the first time, we report that hypoxia can affect sex differentiation and sex development of zebrafish (Danio renio), leading to 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). The increase in males was associated with downregulations of various genes controlling the synthesis of sex hormones (i.e., 3β-HSD, CYP11 A, CYP19A, and CYP19B) as well as an increase in the testosterone/estradiol ratio. The male-dominated populations caused by hypoxia will have reduced reproductive success, thereby threatening the sustainability of natural fish populations. © 2006 American Chemical Society.link_to_subscribed_fulltex