Comparison of growth, diet and food consumption of sea-run and lake-dwelling Arctic charr

Sea-run post-smelt Arctic charr Salvelinus alpinus (15-26 cm) from Storvatn , northern Norway (70 degrees 39'48"N) had significantly higher average spe cific growth rates in two years (1.64 and 1.66) than the corresponding lake -dwelling charr (0.53 and 1.20). The post-smelts displayed fast compensator y growth in the first 2-3 weeks of their sea residency, but then almost sto pped growing prior to their return to fresh water. Lake-dwelling charr grew more evenly during the same time period. Thus, the anadromous charr may re turn to the lake after only 5-6 weeks in the sea, because the potential to maintain a high growth rate in the sea is reduced. The marine diet consiste d mainly of the two crustacean plankton species Calanus finmarchicus and Th ysanoessa sp. (88%), and less of fish (6%), insects (4%) and benthos (2%). The diet of lake-dwelling charr consisted mainly of insects (58%, mostly ch ironomid pupae) and zoobenthos (29%), and less of zooplankton (13%) during the same time period. Although post-smelts had the highest growth rates, th ey had significantly lower food consumption rates and higher frequencies of empty stomachs than the corresponding lake-dwelling fish. Possible explana tions for this paradox are discussed in relation to stomach evacuation rate s, water temperature, feeding behaviour and the energy content of the food in the two environments. (C) 2000 The Fisheries Society of the British Isle s.