Effects of thermal regime on energy and nitrogen budgets of an early juvenile Arctic charr, Salvelinus alpinus, from Lake Inari

The feed intake, growth, oxygen consumption and ammonia excretion of juvenile Arctic charr were measured over period of four weeks at different temperatures which were either constant (11.0, 14.4, 17.7 °C) or fluctuated daily (14.3 ± 1 °C). Maximum feed intake was estimated to occur at 14.3 °C, while oxygen consumption and nitrogen excretion were highest at the highest temperature, and growth rate was estimated to be highest at 13.9 °C. Feed conversion efficiency was estimated to be highest at 13.2 °C, where over 62.7% of ingested energy was allocated to growth. Metabolic rate accounted for 16–30% of ingested energy and nitrogen excretion was under 3% of ingested energy. The nitrogen budget was under similar thermal influences to the energy budget. Thermal fluctuation increased metabolic rate, but not feed intake, leading to a reduction in feed conversion efficiency under fluctuating temperature conditions.