Nitrate-induced elevations in circulating sex steroid concentrations in female Siberian sturgeon ( Acipenser baeri) in commercial aquaculture

Abstract

Although nitrate is a ubiquitous component of aquatic environments, and has become a global pollutant in a variety of aquatic systems, it has only recently begun to receive attention for its ability to alter endocrine function. Aquaculture environments with limited water exchange often contain nitrate concentrations far in excess of natural environments, yet nitrate's impact on the reproductive health and endocrine function of commercially important species residing in these environments has not been investigated. Two experiments were conducted evaluating the effects of elevated nitrate on cultured Siberian sturgeon ( Acipenser baeri). The first experiment compared the effects of a 30 day exposure to 11.5 ± 0.36 and 57 ± 2.18 mg/L nitrate-N concentrations on plasma cortisol (F), glucose, 17β-estradiol (E 2), testosterone (T) and 11-ketotestosterone (11-KT) concentrations. The second experiment was similar to the first but evaluated concentrations of 1.5 ± 0.057 and 57 ± 1.52 mg/L nitrate-N. In both experiments, after 30 days of exposure to a given nitrate concentration, blood samples were obtained at time 0, and a portion of those fish were then placed under confinement stress for a period of 6 h to evaluate whether nitrate affects the associated stress response. The fish were bled at 1 h and 6 h during the confinement period. Results revealed that 57 mg/L nitrate-N exposure was associated with an increase in plasma T, 11-KT and E 2 concentrations at time 0, but did not alter the associated stress response defined by elevated plasma cortisol concentrations. An additional measure of the stress response, plasma glucose concentration, however, was altered by nitrate exposure during the 6 h period of confinement stress in Experiment 1, but was not in Experiment 2. These findings demonstrate that nitrate has the potential to disrupt endocrine function and possibly secondary stress responses in cultured Siberian sturgeon.