COMPARTMENTAL DISTRIBUTION OF FREE AMINO-ACIDS AND PROTEIN IN DEVELOPING YOLK-SAC LARVAE OF ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS)

Free amino acids (FAA) and protein have been measured in whole laborat ory-readed halibut larvae and on dissected individuals separated into yolk and body compartments. At hatching both FAA and protein are mainl y located in the yolk compartment. During the first 12 d of the yolk-s ac stage more than 70% of the FAA pool disappeared from the yolk witho ut any significant changes in the yolk protein pool. This suggests dif ferent uptake mechanisms for FAA and protein from the yolk, and a sequ ential utilisation of the endogeneous reservoirs of free and protein a mino acids in Atlantic halibut larvae. The data suggest that in the ea rly yolk-sac stage FAA enter the embryo from the yolk and are utilised both for energy and protein synthesis. Later on when the free pool ca nnot fulfil the nutritional requirements, additional amino acids are r ecruited from yolk protein. Of the total amino acids (free + protein a mino acids) present at hatching ca. 60% will be used as precursors for body protein synthesis while the remaining 40% are used as fuel in th e larval energy metabolism.