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 acclimated to 11·0) C for 3 weeks, and then one group was maintained at 11·0) C and others were exposed to 14·4) Cconst, 17·7) C_const or a diel fluctuating temperature of 14·3° C ± 1° C (14·3° C_fluc). Routine rates of oxygen consumption and ammonia excretion were measured over 10 days before the temperature change and over 31 days following the change. Measurements were made on fish that were feeding and growing. The temperature increase produced an immediate increase in oxygen consumption. There was then a decline over the next few days, suggesting that thermal acclimation was rapid. For groups exposed to constant temperature there was an increase in oxygen consumption ( M _accl, mg kg⁻¹ h⁻¹) with increasing temperature ( T ), the relationship being approximated by an exponential model: M _accl= 46·53e0·^{086 T} . At 14·3° C_fluc oxygen consumption declined during the 3–4 days following the temperature shift, but remained higher than at 14·4° C_const. This indicates that small temperature fluctuations have some additional influences that increase metabolic rate. Ammonia excretion rates showed diel variations. Excretion was lower at 11° C_const than at other temperatures, and increases in temperature had a significant effect on ammonia excretion rate. Fluctuating (14·3° C_fluc) temperature did not influence ammonia excretion relative to constant temperature (14·4° C_const).