Bioenergetics of Arctic cod (Boreogadus saida) at low temperatures

The Arctic cod (Boreogadus saida), a key component of the marine food web of Canadian high Arctic waters, occurs at temperatures close to or below zero. We established a complete energy budget for this Arctic fish, based on laboratory measurements of consumption (C), growth (G), respiration (R), egestion (F), and excretion (U) at about 0 degrees C. An average (N = 3) energy budget for individual juvenile Arctic cod fed live Arctic zooplankton was 100C = 50G + 24R + 9SDA + 3F + 6U + 8Z, where SDA is specific dynamic action (derived from previously published studies) and Z included activity and unaccounted energy. Eight determinations of total energy budgets for fish fed to satiation accounted for 72-104% of the energy consumed. Maximum daily rations and growth rates were dependent an fish size and the energy content of prey. Although maximum daily rations were similar for small fish fed different prey, diets of Calanus copepods (high energy content) resulted in faster growth rates than diets of Themisto amphipods or capelin (Mallotus villosus) fillets. Both consumption and respiration rates were low at temperatures close to 0 degrees C. The net result was slow growth rates, although the assimilation efficiency was about 80%. Because of slow growth of individuals, the relatively high annual production of Arctic cod mainly reflects their large standing biomass.