Proteins and Amino Acids ( QUANTITATIVE REQUIREMENTS OF AMINO ACID)

Quantitative requirements by salmonids for the ten indispensable amino acids were determined by feeding linear increments of one amino acid at a time in a test diet containing an amino acid profile identical with whole egg protein except for the amino acid tested. Replicate groups of fish were fed the diet treatments until gross differences appeared in the growth of test lots. An Almquist plot of growth response indicated the level of amino acids required for maximum growth under those specific test conditions. Diets were designed to contain protein at or slightly below the optimum protein requirement for that species and test condition to assure maximum utilization of the limiting amino acid. A comparison of the requirements for the ten indispensable amino acids between species.
A recent innovation has been the use in test diets of proteins relatively deficient in a given essential amino acid. Thus combinations of fishmeal and zein have been used in test diets to define the requirement of rainbow trout for arginine. Diets containing different relative amounts of casein and gelatin showed that an increase in the level of protein-bound arginine from 11 to 17 g/kg resulted in a significant increase in the growth of channel catfish.
1/ Expressed as percent of dietary protein. In parentheses, the numerators are requirements as percent of dry diet, and the denominators are percent total protein in the diet
2/ In the absence of cystine
3/ Methionine plus cystine
4/ In the absence of tyro sine
5/ Phenylalanine plus tyrosine
Arginine requirement of rainbow trout has been determined from a conventional dose/response (growth) curve and also by measuring the tissue (blood and muscle) levels of free arginine in groups of trout given increasing amounts of dietary arginine. After the dietary requirement of the trout for arginine has been met, any further increase in arginine intake led to an increase in the concentration of free arginine in blood and muscle. Good agreement was obtained between the two methods.
The data suggest that real differences exist between fish species in their requirement for certain amino acids. This leads to difficulties in formulating the protein component of practical diets for those species whose amino acid requirements are not yet known. A possible solution is to use, for each amino acid, the highest level required by any of those species for which data is available. The need for further quantitative data on the amino acid requirements of fish, especially those actually or potentially useful as farm animals, is obvious.