PHYSIOLOGICAL ENERGETICS OF DEVELOPING EMBRYOS AND YOLK-SAC LARVAE OFATLANTIC COD (GADUS-MORHUA) .2. LIPID-METABOLISM AND ENTHALPY BALANCE

This paper presents quantitative data for the changes in the contents of total lipids, lipid classes and their associated fatty acids, toget her with the changes in caloric contents of developing eggs and yolk-s ac larvae of Atlantic cod (Gadus morhua L.). During development betwee n Day 0 to 28 post fertilisation, 32% of catabolic metabolism was fuel led by lipids. On a mass-specific basis, polar lipids (mainly phosphat idyl choline) contributed 60%, and neutral lipids (mainly triacylglyce rol) contributed 40% to this catabolic component, with each class supp lying similar amounts of fatty acids as fuel. The fatty acids supplied by phosphatidyl choline were catabolised non-selectively (i.e. in pro portion to their presence in the egg), with about half of them being p olyunsaturated. However, of the fatty acids esterified in triacylglyce rol, the larvae showed an apparent oxidation preference for monoenes o ver polyunsaturates or saturates. Routine rates of oxygen consumption and ammonia production were related to the caloric contents of the egg s and larvae in order to derive an enthalpy balance equation (of the f orm P = C + R + E) for an Atlantic cod larva during its period of endo genous nutrition. For the interval of Day 0 to 25 post fertilisation ( the period of yolk dependence), integration of the physiological and c aloric data revealed that Atlantic cod larvae conserved 53% of yolk en thalpy (C) for growth (P), 42% was dissipated due to metabolism (R) wh ile only 5% was lost via excretion (E).