RESPIRATORY METABOLISM OF TILAPIA MOSSAMBICA (TELEOSTEI) .2. EFFECT OF SIZE, TEMPERATURE, SALINITY AND PARTIAL PRESSURE OF OXYGEN

Tilapia mossambica (Teleostei) weighing 5 to 80 g were acclimated at 30°C to salinities of 0.4‰ (tap water), 12.5‰ (50% sea water) and 30.5‰ (100% sea water). Their respiration was measured at routine activity and the partial pressure of ambient oxygen gradually reduced from 250 to 50 mm Hg. Respiration is salinity-dependent; the proportionate ability to use oxygen in any one salinity is - above the critical pO2 -the same in all experimental groups. This ability is a function of temperature and increases from 15° to 30°C, becoming temperature independent from 30° to 40°C as long as the pO2 remains above 150 mm Hg. At 50 mm Hg pO2, the limiting effect of oxygen causes a decrease in metabolic rate. This limiting effect is minimal in 80 g fish kept in an isotonic medium (12.5‰ S), allowing greater scope for activity and a higher rate of oxygen uptake. © 1969 Springer-Verlag.