Effects of protein-, peptide- and free amino acid-based diets in fish nutrition

Abstract

In the present review, we summarize data related to the utilization of purified diets formulated with the purpose of determining the amino acid requirements in fish independent of the ontogenetic stage and the morphological characteristics of the digestive tract. Expanding present knowledge on the formulation of protein, free amino acid (FAA) and synthetic dipeptide-based diets can provide possible insights that might lead to a better understanding of the mechanism of amino acid utilization in the growth of fish. Differences exist in the utilization of protein, dipeptides or free amino acids for growth between stomach-possessing and stomachless fish with respect to their response to manipulating the proportion of protein and dipeptides in the formulas. Free amino acid-based diets are uniformly inferior. The effects of diet manipulation on indispensable FAA concentrations in the body (muscle) are not simply the result of deamination or the protein synthesis/degradation ratio. The hydroxyproline/proline ratio was confirmed to be of value in quantifying muscle collagen degradation/synthesis and can perhaps be used to quantify the amino acid requirement necessary to maximize the utilization (deposition) of dietary amino acids. In summary, indispensable amino acid requirements for maximum growth in fish can be addressed using diets formulated from protein/peptide/FAA sources.