title: The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.
abstract: The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees 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 degrees C to 15 degrees 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 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees 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 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), 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.
authors.affiliation: Centre for Fish Metabolism and Energetics, Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada. alsopd@mcmaster.ca
authors.forename: D H
authors.initials: DH
authors.lastname: Alsop
authors.forename: J D
authors.initials: JD
authors.lastname: Kieffer
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D004734:Energy Metabolism; D017672:Nitrogen Compounds / Q000378:metabolism; D010101:Oxygen Consumption; D011506:Proteins / Q000378:metabolism*; D013550:Swimming / Q000502:physiology; D013696:Temperature; D017210:Tilapia / Q000502:physiology*
chemical_list: D017672:Nitrogen Compounds; D011506:Proteins