Seasonal variation in body composition of Arctic char, Salvelinus alpinus, from an ultraoligotrophic alpine lake

Seasonal pattern of energy content was determined in a population of Arctic char, Salvelinus alpinus (L.), living in an ultraoligotrophic alpine lake (altitude 1100 m) located in central Norway (62degrees5'N). Specific somatic energy content varied between 4.3 and 6.1 kJ.g(-1) in spawners and between 4.8 and 6.6 kJ.g(-1) in immatures. Corresponding values for specific somatic lipid energy were 0.5-1.6 kJ.g(-1) for spawners and 0.7-2.1 kJ.g(-1) for immatures. The temporal pattern in storage energy residuals (deviation from mean storage energy, all sampling periods pooled) indicated that total, protein and lipid energy accumulated in the autumn and early winter. This increase was followed by a winter decrease in somatic energy (January to April). A new increase in total somatic energy and somatic lipid energy occurred during late winter (March/April to June), while the lake was still ice covered and water temperatures ranged between 0.5 and 2.5degreesC. The observed seasonal pattern of specific energy storage and lipid deposition demonstrated a considerable potential for energy accumulation in Arctic char at low temperatures. It is discussed whether freshwater lakes at high altitudes or latitudes represent a temperature-stabilised and predictable environment in contrast to the variable temperature experienced in the corresponding terrestrial system.