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 f ish, 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 f ed live Arctic zooplankton was 100C = 50G + 24R + 9SDA + 3F + 6U + 8Z, where SDA is specific dynamic action (derived from previously publish ed studies) and Z included activity and unaccounted energy. Eight dete rminations 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. Alth ough maximum daily rations were similar for small fish fed different p rey, diets of Calanus copepods (high energy content) resulted in faste r growth rates than diets of Themisto amphipods or capelin (Mallotus v illosus) fillets. Both consumption and respiration rates were low at t emperatures 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.