PLASMA AMINO-ACID LEVELS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The time course of plasma amino acid concentrations was studied in adu lt rainbow trout (300 g mean body weight). After a starvation period o f 2 days fish were force-fed either with fish protein concentrate or a mixture of acidic casein ana Na-caseinate at a rate of 0.32% CP (N'6. 25) of body weight. Peak levels occurred for feeding fish protein conc entrate 6-12h and for the casein mix 18 h post-feeding. The increase o f the essential amino acids was closely correlated to the amino acid p rofile of the test proteins, whereas the concentration differences of the non-essential amino acids were at no time correlated to the amino acid pattern of fish protein concentrate or even negatively correlated in case of casein. The limiting amino acids in the test proteins were determined by ranking the average concentration increases (decreases) of the individual essential amino acids. Accordingly, arginine and hi stidine were most deficient in casein; in fish protein concentrate try ptophan seems to be the first limiting amino acid, followed by isoleuc ine.