The effects of acclimation temperature (30°, 20°, and 15°C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30°C to 15°C, resting oxygen consumption (MO2) and carbon dioxide excretion (MCO2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30°C, resting MO2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15°C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30°C and 15°C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15°C and 5°C, respectively. Temperature also had a pronounced effect on critical swimming speed (U(Crit)). Tilapia acclimated to 30°C had a U(Crit) of 5.63 ± 0.06 body lengths/s (BL/s), while, at 20°C, U(Crit) was significantly lower at 4.21 ± 0.14 BL/s. Tilapia acclimated to 15°C were unable or unwilling to swim. As tilapia swam at greater speeds, MO2 increased exponentially; MO2min and MO2max were 5.8 ± 0.6 and 21.2 ± 1.5 μmol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30°C, instantaneous protein use while swimming at 15 cm/s (~1.7 BL/s) was 23%, and at U(Crit) (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, ~50% U(Crit)), MO2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.
ASJC Scopus subject areas
- Animal Science and Zoology