Summary
Respiratory properties of piranha blood are distinguished from those of other fish primarily by the high CO2 buffering capacity (ΔHCO3-/ΔpH = 18.6mmol/L for oxygenated blood and 39.1 mmol/L for deoxygenated blood). The concentration of nucleoside triphosphates CNTP) and the half-saturation tension (P50) of whole blood were found to be inversely related to body size. The higher p50 in smaller fish, analogous to values obtained in previous studies involving interspecies comparisons, could be adaptive to higher weight-specific metabolic rate. Both ATP and guanosine triphosphate (GTP) lowered the oxygen affinity of purified hemoglobin solutions, accounting for the size-dependent correlation of P50 and NTP concentration in whole blood. While similar in concentration in red cells, GTP is more potent than ATP as an allosteric modifier of hemoglobin function.