Date of Award

January 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Steve Kelsch

Abstract

Copper (Cu) is a component of several aquatic pesticides often used to target noxious algae, but at high concentrations may elicit toxic effects on non-target organisms such as fish. The severity of Cu toxicity varies widely by fish species, Cu concentration, duration of exposure, and water quality. Hypoxia is a widely occurring aquatic stressor that is also a potential side effect of Cu application due to increased oxygen demand from algae decay. Because Cu and hypoxia stress may occur in concert, it is important to understand and quantify their combined effects. Critical swimming speed (Ucrit) tests are an efficient and non-lethal means of quantifying the acute effects of environmental stressors on a fish's metabolic scope for activity or available energy. The change in swimming speed (Delta Ucrit) as opposed to raw Ucrit of bluegill sunfish (Lepomis macrochirus) was measured in response to Cu and hypoxia stress in an attempt to remove variation in individual swimming ability. Using a variable speed swim chamber, Delta Ucrit was measured in a 2x3x2 factorial design with Cu concentration (0 and 1 mg Cu/L), duration of Cu exposure (24, 48, and 96 hrs) and dissolved oxygen (DO) concentration (>8 (saturated) and 2 mg O2/L (low)) as fixed factors. Hematocrit and gill sections were also analyzed. A significant, non-additive interaction between [Cu] and [DO] was observed. Duration of Cu exposure did not appear to be a substantial factor. At saturated DO, Delta Ucrit was significantly greater in bluegill exposed to 1mg Cu/L. At low DO, Delta Ucrit was significantly lower in bluegill exposed to 1mg Cu/L. Gill damage and increased hematocrit with exposure to Cu and hypoxia were also observed. Gill damage likely increased gill permeability that may have resulted in ion efflux, causing hemoconcentration by plasma water displacement ultimately resulting in increased cardiac stress. Increased Delta Ucrit at saturated DO may have been due to an antibiotic or limiting nutrient effect coupled with decreased ion efflux via decreased lamellar perfusion. Substantially more variation was left unexplained (31.7% vs. 79.1%) by measuring Delta Ucrit rather than raw Ucrit which resulted in greater statistical resolution.

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