Date of Award

Spring 5-2017

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Heather Hamlin

Second Committee Member

Rebecca Van Beneden

Third Committee Member

Mary Tyler

Abstract

Nitrate accumulation in aquatic reservoirs from agricultural pollution has often been overlooked as a material water quality hazard, yet scientific evidence suggests negative effects on human and wildlife health following nitrate exposure. This study examines a variety of metabolic physiological responses to elevated nitrate exposure in zebrafish, Danio rerio. Embryos were exposed to 0, 5, 10, 50 and 100 mg/L NO3-N, andto a counter ion control (CIC) treatment annotated as 100 mg/L CIC to determine the effects of nitrate contamination on thyroid biomarker mRNA transcript abundance. These data revealed no significant differences in mRNA transcript abundance up to 100 mg/L NO3-N. Exposure to 100 mg/L NO3-N yielded a 0.5 fold down-regulation in thyroid stimulating hormone receptor (tshr) mRNA transcript abundance, and an 0.5 fold upregulation in sodium iodide symporter (slc5a5) mRNA transcript abundance. In addition, exposure to 100 mg/L CIC yielded a 0.5 fold down-regulation in tshr mRNA transcript abundance, suggesting that the down-regulation seen in the 100 mg/L NO3-N treatment group may be due to the carrier ion and not the nitrate ion. In a second experiment, embryos were exposed to 0, 10, and 100 mg/L NO3-N, and to counter ion control treatments of 10 and 100 mg/L CIC with both immersion and injection techniques to examine metabolism by measuring changes in oxygen consumption rates in vivo. Immersion exposures did not induce significant changes in oxygen consumption rates, yet the same concentrations of nitrate-nitrogen induced significant changes when microinjected through the embryo chorion. Injection of 10 and 100 mg/L NO3-N downregulated oxygen consumption rates compared to the control treatment group. Injection of 100 mg/L CIC also significantly down-regulated oxygen consumption rates compared to the control treatment group. Interestingly, the 100 mg/L NO3-N treatment further downregulated oxygen consumption rates compared to the 100 mg/L CIC treatment, suggesting the potential for additive effects in this laboratory nitrate compound between the counter ion and the ion of interest. These data confirm that elevated nitrate exposure can alter normal metabolic activity by changing thyroid biomarker mRNA transcript abundance, and oxygen consumption rates. The biological significance of 0.5 fold changes in thyroid biomarker mRNA transcript abundance is limited due to such a small fold change. These results also support the need for regularly examining the counter ion of laboratory nitrate compounds while conducting research with developing zebrafish, as counter ion control treatment groups produced significant data in these studies. Lastly, these results justify examining different routes of laboratory nitrate exposure, as the chorion may act as an effective barrier to nitrate penetration, which may lead to conservative estimate concentrations of significant effects. This investigation into nitrate’s effects on the metabolic activity of the developing zebrafish may help to refine laboratory nitrate research using zebrafish as a model organism.

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