Baby fish exposed to hormone-laden water from Indiana farms were more likely to become male, according to a new study from Purdue University. Researchers raised fathead minnow embryos in water taken from two separate streams, each contaminated with a variety of hormones from fertilizer used on nearby fields. While fish typically birth roughly equal numbers of males and females, the fish in the study turned 60 percent male.
Livestock naturally excrete estrogen and testosterone, but many animals are given additional synthetic hormones to expedite growth. Researchers found both kinds of hormones in 80 percent of their water samples. The study’s lead author, Maria Sepulveda, admitted that other factors such as water temperature and pesticides could also influence fish gender, but cautioned that this type of gender skewing could negatively affect fish populations over time.