<P> Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean . </P> <P> In August 2017, a report found that the US meat industry is responsible for the largest - ever dead zone in the Gulf of Mexico . Runoff from widespread manure and fertilizer pollution contaminated water from the Heartland to the Gulf . Much of this pollution comes from the vast quantities of corn and soy used to raise meat animals for agribusiness companies, like Tyson . </P> <P> Low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning . </P> <P> In a study of the Gulf killifish by the Southeastern Louisiana University done in three bays along the Gulf Coast, fish living in bays where the oxygen levels in the water dropped to 1 to 2 parts per million (ppm) for three or more hours per day were found to have smaller reproductive organs . The male gonads were 34% to 50% as large as males of similar size in bays where the oxygen levels were normal (6 to 8 ppm). Females were found to have ovaries that were half as large as those in normal oxygen levels . The number of eggs in females living in hypoxic waters were only one - seventh the number of eggs in fish living in normal oxygen levels . </P>

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