Factorial aerobic scope is independent of temperature and primarily modulated by heart rate in exercising Murray Cod (Maccullochella peelii peelii)

Several previous reports, often from studies utilising heavily instrumented animals, have indicated that for teleosts, the increase in cardiac output ( ) during exercise is mainly the result of an increase in cardiac stroke volume (VS) rather than in heart rate (fH). More recently, this contention has been questioned following studies on animals carrying less instrumentation, though the debate continues. In an attempt to shed more light on the situation, we examined the heart rates and oxygen consumption rates ( ; normalised to a mass of 1 kg, given as ) of six Murray cod (Maccullochella peelii peelii; kg) equipped with implanted fH and body temperature data loggers. Data were determined during exposure to varying temperatures and swimming speeds to encompass the majority of the biological scope of this species. An increase in body temperature (Tb) from 14°C to 29°C resulted in linear increases in (26.67-41.78 μmol min−1 kg−1) and fH (22.3-60.8 beats min−1) during routine exercise but a decrease in the oxygen pulse (the amount of oxygen extracted per heartbeat; 1.28-0.74 μmol beat−1 kg−1). During maximum exercise, the factorial increase in was calculated to be 3.7 at all temperatures and was the result of temperature-independent 2.2- and 1.7-fold increases in fH and oxygen pulse, respectively. The constant factorial increases in fH and oxygen pulse suggest that the cardiovascular variables of the Murray cod have temperature-independent maximum gains that contribute to maximal oxygen transport during exercise. At the expense of a larger factorial aerobic scope at an optimal temperature, as has been reported for species of salmon and trout, it is possible that the Murray cod has evolved a lower, but temperature-independent, factorial aerobic scope as an adaptation to the largely fluctuating and unpredictable thermal climate of southeastern Australia

Energy requirements of female Macaroni Penguins breeding at South Georgia

1. Breeding female Macaroni Penguins (Eudyptes chrysolophus) were implanted with heart rate, temperature and depth data loggers in order to estimate their rate of energy expenditure from heart rate. 2. The estimated average daily metabolic rates (ADMR) of birds during the brood and crèche phases of the breeding season were 8.17 ± 0.44 W kg-1 and 8.24 ± 0.41 W kg-1, respectively. There was no significant difference between these estimates and the pooled ADMR for all birds was 8.22 ± 0.38 W kg-1. 3. Metabolic rate while the penguins were at-sea was 9.03 ± 0.39 W kg-1 and this was significantly greater than the metabolic rate of 6.27 ± 0.38 W kg-1 while they were on-shore. 4. Females undertook shorter foraging trips during the crèche phase than during the brood phase. 5. When considered as a breeding pair, Macaroni Penguins expend more energy in raising their chick during the crèche phase of the breeding season as the male assists in provisioning the chick only at this time.</p