Manure runoff from concentrated animal farming operations in Indiana is impacting the reproduction and gender of wild fish, according to this study. The hormone-laden waste contaminates local waterways, leading to 60% of fish embryos being male (in a control setting with fish in uncontaminated water, the ration was close to 50:50). The study’s authors and other fish experts worry that the contaminants may lead to a decline in fish populations. Additionally, waterways contaminated by animal farms had 50% less fish diversity and a 28% higher adult minnow death rate when compared to the uncontaminated waterway.

[Abstract excerpted from the original report.]

“Concentrated animal feeding operation (CAFO) manure is a cost-effective fertilizer. In the Midwest, networks of subsurface tile-drains expedite transport of animal hormones and nutrients from land-applied CAFO manure to adjacent waterways. The objective of this study was to evaluate impacts of land-applied CAFO manure on fish populations and communities. Water chemistry including hormone, pesticide, and nutrient concentrations was characterized from study sites along with fish assemblage structure, growth, and endocrine disruption assessed in selected fish species. Although most CAFO water samples had hormone concentrations <1 ng/L, equivalent concentrations for 17à-E2 and 17␣-TB peaked at >30 ng/L each during the period of spawning, hatching, and development for resident fishes. CAFO sites had lower fish species richness, and fishes exhibited faster somatic growth and lower reproductive condition compared to individuals from the reference site. Fathead minnows (Pimephales promelas) exposed to CAFO ditchwater during early developmental stages exhibited significantly skewed sex ratios toward males. Maximum observed hormone concentrations were well above the lowest observable effect concentrations for these hormones; however, complexities at the field scale make it difficult to directly relate hormone concentration and impacts on fish. Complicating factors include the consistent presence of pesticides and nutrients, and the difference in temperature and stream architecture of the CAFO-impacted ditches compared to the reference site (e.g., channelization, bottom substrate, shallow pools, and riparian cover).”