Plasma chemistry, erythrocyte, and spleen responses to fatigue and recovery in Ucrit versus chase protocols in mahi-mahi (Coryphaena hippurus), a high-performance pelagic teleost.

We compared responses in blood plasma chemistry, red blood cells, and spleen to fatigue and recovery in Ucrit versus chase protocols in mahi-mahi (Coryphaena hippurus). Immediately after 20-min Chase to fatigue, plasma lactate levels were elevated approximately 6-fold, but the increase was only 2-fold in fish sampled at the point of fatigue in the Ucrit test. Plasma Mg2+ was elevated > 2-fold by the Chase treatment, but only 1.5-fold by the Ucrit treatment. In both protocols, increased plasma ions contributed about 60% of the 1.14-fold elevation in plasma osmolality, while increased glucose and lactate were responsible for about 40%. Elevations in plasma cortisol (4.3-fold), ammonia (1.5-fold), Na+ and Cl- (1.1-fold), and red blood cell (RBC) swelling were comparable in the two treatments. Increases in plasma glucose, RBC pHi, and splenic discharge of RBCs tended to be greater in the Ucrit treatment. In both treatments, most parameters were restored to control levels by 4 h recovery despite very different tissue metabolite profiles and patterns of elevation and recovery of oxygen consumption documented in a companion respirometry study. The possible roles of elevated plasma Mg2+ and ammonia concentrations in causing fatigue are discussed. In combination, the respirometry, tissue metabolite, blood plasma, RBC, and spleen data suggest a greater anaerobic contribution to exercise metabolism in the Chase protocol, with broader implications for catch-and release angling.