Exploring the Effects of Early Life Stage Nitrate Exposure on Male Sexual Development and Reproduction

Abstract

Nitrate is a ubiquitous environmental contaminant that enters aquatic ecosystems as runoff from agricultural fertilizers and industrial byproducts. Previous animal studies indicate that nitrate acts as an anti-androgen in adult male vertebrates. Because androgens are known to influence sexual development and stimulatesecondary sex characteristics and reproductive behaviors in male fish, this study sought to explore the impacts of early life stage nitrate exposure on these processes. The main objective of this study was to identify the potential endocrine disrupting effects of nitrate across multiple levels of biological organization in male fathead minnows. Larvae less than 1 day post hatch were divided into three groups: 1) control, 2) low nitrate (50 mg/L NO3), and 3) high nitrate (100 mg/L NO3) and exposed for 35 days. Gonadal expression of sex-steroid related genes was assessed in a subset of fish immediately following exposure. The remaining fish in each exposure group were raised in clean water until sexual maturity (115 dph) and then subjected to a 21-day breeding study, after which male secondary sex characteristics were assessed. Gene expression analysis revealed that male fish in the high nitrate group had significantly decreased expression of a key enzyme in the sex steroid synthesis pathway, suggesting decreased androgen synthesis following exposure. However, there was not sufficient evidence to suggest that nitrate impacts the expression of male secondary sex characteristics or the ability of the males to successfully reproduce.