AN ABSTRACT OF THE THESIS OF ROGER DEAN MEYERHOFF for the degree of DOCTOR OF PHILOSOPHY

approved: La'rn J. Weber Acid-base balance in ammoniotelic fish can be accounted for by the concentrations and net flux rates of four generalized independent variables. The physicochemical principles of acid-base chemistry determine the quantitative interaction of acids and bases in an aqueous solution. In a given medium, acid-base balance is the instantaneous net result of input and output rates of acids and bases, as represented by independent variables. Control of acid-base balance is determined by regulation of input and/or output rates of at least some independent variables. For the vascular compartment, the four independent variables of interest are strong ion difference, total weak acid, total carbon dioxide and total ammonia. Acid-base balance in the vascular compartment depends on the input and output rates of all independent variables. Concentrations of dependent variables, such as H+ and HCO3 are set by the concentrations of independent variables and the laws which govern conservation of mass, electrical neutrality and equilibrium limitations in Redacted for Privacy dissociation reactions. For the vascular compartment of teleost fish, input and/or output of independent variables may occur at the gills, kidney, tissue and gut. Regulation of acid-base balance is known to occur at the gills and kidney. To regulate acid-base balance in the vascular compartment, teleost fish rely on their capacity to control the total weak acid concentration and the strong ion concentration difference of their blood. For rainbow trout, fluctuations in exercise levels have the potential to alter the acid/base flux rates and acid-base balance of the vascular compartment. In order to assess how acid/base load elimination is amended by rainbow trout to accommodate an increase in their level of sustained aerobic exercise, elimination of total carbon dioxide, total ammonia and lactate at the gills was monitored and net excretion of acid by the kidney was measured. Characteristics of blood acid-base balance and acid/base load loss were compared. Total carbon dioxide, total ammonia and net acid efflux rates rose in Shasta strain rainbow trout that were switched from 20% to 45% of their maximum swimming velocity (U-crit), when compared to those rates of fish maintained at 20% U-crit. The increased total carbon dioxide loss rate followed an augmented oxygen consumption rate and the respiratory coefficient did not change significantly. The elevated oxygen consumption rate and total carbon dioxide efflux rate were initially accomplished by a significant but transient increase in the change of blood [023 and total [CO2] at the gills. This transient increase was followed by an increased cardiac output rate to maintain the augmented oxygen consumption rate and total carbon dioxide efflux rate. For fish switched from 20% to 45% U-crit (treatment fish), output of titratable acid, inorganic phosphate and net acid carried by the urine significantly increased over the 72 hr experimental period. The slight respiratory and metabolic acidosis found for treatment fish was followed by a significant increase in blood [HC0], characteristic of metabolic alkalosis. A rise in blood Pco2 and a significant rise in blood lactate probably accounted for the initial acidosis. Increased loss of NH and a decreased loss of Na+ across the gill may have accounted for the elevated [HC0J via a change in blood strong ion concentration difference. Re-establishment of normal acid-base status may have relied on increased net influx of Cl at the gill due to increased blood [HC0]. Renal acid excretion did not wholly account for any change found in blood acid-base balance. Exercise and Acid-Base Balance in Rainbow Trout