Physiological responses of flatfish to temperature : a comparative study
The respiratory metabolism of three flatfish species, Platlchthys flesus (L.), Limanda llmanda (L.). and Microstomus kltt (Walbaum) has been investigated in relation to temperature. For the three species, the relationship between standard oxygen consumption and weight at all adaptation temperatures is described by log V02 = log a -I- b log W. Standard rates are evident .15 h after handling. Subjection of P. flesus to temperature change suggests a Precht type III compensatory response. However, an alternative explanation in terms of excitement metabolism is offered. Standard rates of flatfish are low compared to roundfish. The relationship between swimming speed and oxygen consumption for the three species at 5, 10 and 15 C can be described by log V02 = bx + a. A discrepancy exists between predicted standard oxygen consumption and the intercepts of the oxygen consumption - swimming speed regressions. This may represent a "posture effect". Active metabolic rates are low compared to salmonids. Optimum and critical swimming speeds of flatfish are similar. Flatfish may normally swim at supercritical speeds with rest periods to pay off oxygen debt. Elevated muscle lactate levels indicate that anaerobiosis contribxites 15% of the total energetic expenditure during sub-critical swimming. Swimming is more expensive at higher adaptation temperatures. The response of heart rate to temperature change is similar to standard oxygen consumption. The duration of the intervals of the E.C.G. waveform increases with time irrespective of previous thermal history, possibly reflecting a loss of condition. Haematological properties of blood from 5 and 15 C-adapted P. flesus do not significantly differ. Blood of P. flesus displays Bohr and Root effects. O2 affinity as assessed by P50 values shows no thermo-adaptive properties. In the resting fish, heart rate is the primary cardiovascular adjustment to temperature change, stroke volume changes being relatively small. It is concluded that P. flesus is a thermal-conformer.