| Summary: | Aerobic metabolic rates of embryos and larvae of Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus) were measured and used stoichiometrically to balance the substrates, in the form of free amino acids (FAAs), proteins and lipids, that quantitatively disappeared during development. Calculations reveal that cod embryos and larvae predominantly fuel their metabolism with FAAs (73%) throughout development; in addition, following closure of the blastopore, lipid is also steadily catabolized (27%). Turbot, however, utilize different substrates at separate stages of development. FAAs are predominantly burned during the embryonic stage, while lipids are burned during the yolk-sac stage. From the time of first-feeding, proteins are recruited from body stores and catabolized. Thus, for turbot, free and protein-bound amino acids together contribute 40% to the energy metabolism, while lipids contribute 60%.
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