College of Science and Health Theses and Dissertations

Date of Award

Fall 11-24-2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Science

First Advisor

Jason Bystriansky, PhD

Second Advisor

Windsor Aguirre, PhD

Third Advisor

Carolyn Martineau, PhD

Abstract

Migratory fishes encounter a variety of environmental conditions throughout their life, including changes in salinity, temperature, and dissolved gases. It is important to understand how these fishes are able to acclimate to simultaneous environmental stressors. This thesis examined the physiological interaction of elevated dissolved CO2 (an acid-base disturbance) on osmoregulation during seawater acclimation (an ionoregulatory disturbance) in juvenile white sturgeon (Acipenser transmontanus). Many ion transport mechanisms at the gill involved with acid-base compensation are also required for the regulation of plasma Na+ and Cl+, the predominant extracellular ions. Thus, the interaction between iono- and acid-base regulation has been hypothesized. In this thesis, blood pH (pHe), plasma ion concentrations, white muscle water content, and gill Na+/K+-ATPase (NKA) and Na+/K+/2Cl- cotransporter (NKCC) abundance were examined over a 10-day seawater (SW) acclimation period under normocarbia (NCSW) or during prior and continued exposure to hypercarbia (HCSW), and compared to a normocarbic freshwater (NCFW) control. Hypercarbia induced a severe extracellular acidosis (from pH 7.65 to pH 7.2) in HCSW sturgeon, and these fish had a 2-fold greater rise in plasma osmolarity over NCSW by day 2 of SW exposure. Interestingly, pHe recovery in HCSW was associated more prominently with an elevation in plasma Na+ prior to osmotic recovery and more prominently with a reduction in plasma Cl- following osmotic recovery, indicating a biphasic response as the requirements of osmoregulation transitioned from ion-uptake to ion-excretion throughout SW acclimation. These results imply a prioritization of osmoregulatory recovery over acid-base recovery in this period of combined exposure to acid-base and ionoregulatory disturbances.

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