The oxygen uptake of Sarotherodon niloticus L. and the oxygen binding properties of its blood and hemolysate (Pisces: Cichlidae).

The oxygen consumption of Sarotherodon niloticus L. was found to decline below a critical oxygen concentration of about 2 mg O2/l. An important influence of CO2 on the oxygen affinity of whole blood was observed at all temperatures between 20 and 35 degrees C for gas mixtures containing 5.6% CO2. Purified hemolysate showed extremely high oxygen affinities (p50 = 1.08 mmHg at pH 8.2 and 20 degrees C). Low cooperativity was observed at all temperatures from 20 to 35 degrees C, and pH values between 6.5 and 8.2. The Bohr effect proved to be important at pH values lower than pH 7.5 (phi = delta log P50/delta pH = -0.58 between pH 6.5 and 7.0 at 35 degrees C). The oxygen affinities show high thermal sensitivity without a marked pH influence (delta H value for overall oxygenation at pH was -71.7 kJ/mol). The obtained results are interpreted as adaptations to diurnal variations in ambient temperature and oxygen availability.