Studies on the Nutrition of Marine Flatfish the Essential Amino Acid Requirements of Plaice and Sole

Abstract
Present knowledge of the nutritional requirements of fish is limited to certain species of salmon and trout (e.g. Halver, DeLong & Mertz, 1957; Shanks, Gahimer & Halver, 1962). In view of the current interest in the cultivation of marine flatfish (Shelbourne, 1964) information on their dietary needs is equally desirable. Experience with salmon (DeLong, Halver & Mertz, 1958) has indicated that protein is the largest and most expensive constituent of fish diets and studies on the nutritional value of different food proteins for fish are necessary if the fish are to be reared economically and successfully. A desirable prerequisite to such studies is a knowledge of those amino acids for which the fish has an absolute dietary requirement, i.e. which it cannot itself synthesize from other substances normally available. With most animals these requirements have been identified by growth trials using partially (or wholly) defined diets. The rearing of fish on defined diets is not easy and it seemed in the first instance that an indirect but valid approach might be utilized. If animals are given a radioactively labelled carbon source, such as uniformly labelled [U-14C]glucose a significant amount of the radioactive carbon will be incorporated only into those compounds which the animal can itself synthesize. By isolating the amino acids from the tissue proteins following such a dose the essential amino acids are identified as those which are not radioactive. The amino acids containing radioactivity correspond with the so-called non-essential amino acids.