uence of Temperature and Current Speed on the Swimming Capacity of Lake Whitefis s ciupeaformis

We tested the influence of temperature and water velocity o n metabolic rate and swimming performance of lake whitefish (Coregonus dupeaformis) and cisco (C. artedii) using respirometry techniques. Tests were conducted at 5,12, and 1 P C (speed range 20-102 crnss-'f for lake whitefish and at 12°C (speed range 20-63 cm-s-') for cisco. Fish lengths ranged from 10 to 33 cm (TL). The net aerobic cost of swimming, obtained by subtracting standard from total oxygen consumption, was twice as high for cisco as that for lake whitefish at any swimming speed. However, the standard metabolic rate of lake whitefish was almost the double that of cisco acclimated to the same temperature. Values of metabolic scope for activity coupled with the net cost of swimming showed that coregonines were not good performers compared with most salrnonids. The active metabolic rate, scope for activity, and critical swimming speed for lake whitefish were maximal at 12OC and minimal at 5°C. Swimming endurance of lake whitefish decreased logarithmically wi th swimming speed and was reduced at low temperature, the distance traversed at any given swimmi ng speed being minimal at 5°C. Our results support the hypothesis that the combined effect of high water velocities and low ambient temperature on coregonines' metabolism and swimming performance may be a more important factor than specific spawning temperature in the timing of the early reproductive migration of anadromous coregonines in the Eastmain River, James Bay.