Increases in arterial blood oxygen during exercise in the lemon shark (Negaprion brevirostris)

Polyethylene cannulae were implanted in pre- and post-branchial blood vessels allowing nonstressful blood sampling over a variety of activity ranges in an active tropical elasmobranch, the lemon shark (Negaprion brevirostris). The P₅₀ was found to be 11.8 Torr at 24°C and pH of 7.7. A Bohr shift of -0.36 was also found. Blood P_o2 and oxygen content were measured during rest, routine swimming, and exercise in unanesthetized, free swimming juveniles. Under all conditions venous oxygen levels were low with venous P_o2 of 7.1±2.7 Torr, and venous oxygen content ( {Mathematical expression}) of 0.56±0.4 vol%. However, a large variability was found in arterial blood measurements. Arterial P_o2 ranged from 7 to 80 Torr, while arterial oxygen content (Ca_o2) varied from 1.6 vol% to 6.8 vol% among ten experimental animals. A significant increase in arterial P_o2, oxygen content, and hematocrit was noted during increased activity. Since the venous system provides little or no oxygen reserve, increased oxygen extraction from the blood ( {Mathematical expression}) appears to be met by an increase in Ca_o2 rather than a decrease in {Mathematical expression}. Mechanisms to accomplish this may include increasing hematocrit and vacular gill shunts.