THE EFFECT OF TEMPERATURE-FLUCTUATIONS ON OXYGEN-CONSUMPTION AND AMMONIA EXCRETION OF UNDERYEARLING LAKE INARI ARCTIC CHARR

Underyearling Lake Inari Arctic charr Salvelinus alpinus were acclimat ed to 11.0 degrees C for 3 weeks, and then one group was maintained at 11.0 degrees C and others were exposed to 14.4 degrees C-const, 17.7 degrees C-const or a diel fluctuating temperature of 14.3 degrees C +/ - 1 degrees C (14.3 degrees C-fluc). Routine rates of oxygen consumpti on and ammonia excretion were measured over IO days before the tempera ture change and over 31 days following the change. Measurements were m ade on fish that were feeding and growing. The temperature increase pr oduced an immediate increase in oxygen consumption. There was then a d ecline over the nest few days, suggesting that thermal acclimation was rapid. For groups exposed to constant temperature there was an increa se in oxygen consumption (M-accl, mg kg(-1) h(-1)) with increasing tem perature (T), the relationship being approximated by an exponential mo del: M-accl=46.53e(0.086T). At 14.3 degrees C-fluc oxygen consumption declined during the 31 days following the temperature shift, but remai ned higher than at 14.4 degrees C-const. This indicates that small tem perature fluctuations have some additional influences that increase me tabolic rate. Ammonia excretion rates showed diel variations. Excretio n was lower at 11 degrees C-const than at other temperatures, and incr eases in temperature had a significant effect on ammonia excretion rat e. Fluctuating (14.3 degrees C-fluc) temperature did not influence amm onia excretion relative to constant temperature (14.4 degrees C-const) . (C) 1998 The Fisheries Society of the British Isles.