Intracellular Buffering and Oxygen Transport in the Pacific Blue Marlin (Makaira nigricans): Adaptations to High-Speed Swimming

Abstract

Blood obtained from Pacific blue marlin captured by hook and line displayed a pronounced acidosis by teleost standards (pH 7.22 ± 0.07 at 25 C), a high PACO₂ (17.3 ± 3.0 torr) and a low PAO₂ (9.7 ± 3.0 torr). Notwithstanding, these properties reflect a major anaerobic component contributing to the acid-base status of blood originating from muscle glycogenolysis during the capture period. This view is consistent with the finding that blood lactate concentration was linearly related to fight time. Marlin is exceptional in its ability to tolerate protons. The buffering capacities (β) of white and red skeletal muscles are 103.8 ± 5.2 slykes and 50.8 ± 3.9 slykes, respectively. The difference between the buffering capacities of the two muscle types likely is related to different rates of adenosine triphosphate (ATP) production and to the different fate of metabolic protons generated in each tissue. The in vitro nonbicarbonate buffering value of whole blood (ΔHC0₃⁻/ApH) also is high when compared with that of other teleosts (β = 21.3 slykes) and represents an important adaptation for extending muscle performance in this species. The relationship between β and hemoglobin concentration is given by the equation β = 1.82[Hb₄] + 3.1. The Bohr coefficient, determined on whole blood following capture, is one of the largest (ø = -1.0 over the pH range 6.957.60) reported for a vertebrate. We propose that having a large Bohr effect is an important strategy for overcoming the high buffering capacity of whole blood, thereby enhancing oxygen delivery to working muscle during high-speed aerobic swimming. It is concluded that the capability of the marlin for high-speed swimming is a result of specialized adaptations to both the O₂ transport and metabolic systems. Enhanced intracellular buffering in both these compartments (blood and skeletal muscle) enables marlin to achieve high work rates during both short-term burst activity and longerterm high-speed swimming required to capture prey.