Publication Date

2019-09-05

Availability

Embargoed

Embargo Period

2021-09-04

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2019-08-13

First Committee Member

Martin Grosell

Second Committee Member

M. Danielle McDonald

Third Committee Member

Marjorie F. Oleksiak

Fourth Committee Member

Michael C. Schmale

Fifth Committee Member

Andrew J. Esbaugh

Abstract

Many ecologically important fishes, including mahi-mahi (Coryphaena hippurus), and their offspring were directly exposed to crude oil following the Deepwater Horizon (DWH) oil spill. Early life stage fish are especially vulnerable to the toxicity of crude oil-derived polycyclic aromatic hydrocarbons (PAHs). In teleosts, yolk sac proteins are the main energy source during development and are usually catabolized into ammonia or urea. Although excretion of these waste products is sensitive to oil exposure, we know little about the underlying mechanisms of this process. This dissertation sought to investigate the ontogeny of ammonia and urea handling in the early life stages of mahi under normal physiological conditions and during the presence of environmental stressor crude oil, as well as to illuminate the potential role of internal convection in ammonia and urea excretion in the early life stages of zebrafish (Danio rerio). Results from this dissertation indicate that mahi mainly excrete urea before hatch and gradually switch to being ammoniotelic after hatch. mRNA levels and the localization of ammonia transporters (Rhag, Rhbg, Rhcg1 and Rhcg2), as well as urea transporter (UT) and sodium hydrogen exchangers (NHE3 and NHE2) were characterized and filled knowledge gaps in our understanding of ammonia and urea excretion in the early life stages of seawater fish. The studies have demonstrated that crude oil increased urea excretion, tissue ammonia and urea levels and mRNA levels of ammonia transporters around the time of hatching in oil-exposed mahi. Observation of decreased ammonia excretion in hatched mahi larvae were unexpected results from this study. This finding lead to the hypothesis that reduced atrial contractility and reduced cardiac output in oil exposed mahi larvae might impair ammonia excretion. Morpholino knockdown of vascular endothelial growth factor (VEGFA) and cardiac troponin T (TNNT2) in transgenic zebrafish produced two independent models lacking internal convection to test this hypothesis. The findings suggest that internal convection may be important to ammonia excretion during the development of zebrafish larvae, at least at higher activity levels. In addition, we observed that oxygen uptake is more dependent on internal convection than ammonia excretion.

Keywords

Rhesus glycoproteins; UT; Toxicity; Ammonia; Urea; Seawater fish

Available for download on Saturday, September 04, 2021

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