Growth responses of juvenile red drum sciaenops ocellatus to dietary phenylalanine and tyrosine can be used to calculate the total aromatic amino acid requirement1,2

Abstract

Background: A current priority in aquaculture is the replacement of fish meal with alternative feedstuffs to ensure the industry's sustainability. However, most alternative protein sources are deficient in at least 1 indispensable amino acid (IAA). Therefore, there is a critical need to establish refined estimates of IAA requirements of fish. Objectives: The objectives of this study were to determine the total aromatic amino acid (TAAA) requirement (Phe + Tyr) and the Tyr replacement value for Phe in juvenile red drum Sciaenops ocellatus. Methods: The TAAA requirement was obtained by feeding juvenile red drum diets that contained incremental amounts of Phe (0.54, 0.84, 1.14, 1.44, 1.74, and 2.04 g/100 g dry diet) and a fixed concentration of Tyr. Because of the TAAA requirement obtained, a second feeding trial was conducted to determine the maximum Tyr replacement value for Phe when a control diet was prepared with an 80%:20% Phe-to-Tyr ratio (Phe:Tyr; 1.60 g Phe/100 g dry diet and 0.41 g Tyr/100 g), and 5 experimental diets were prepared by decreasing the inclusion of Phe and increasing the inclusion of Tyr (Phe:Tyr of 70%:30%, 60%:40%, 50%:50%, 40%:60%, and 30%:70%). Results: Weight gain, the feed efficiency ratio, and the protein efficiency ratio increased 354%, 133%, and 134%, respectively, relative to that of fish fed the basal diet as the Phe concentration increased to 1.44 g/100 g of dry diet; at higher concentrations of Phe, no significant differences were found between treatments. Analysis of the weight gain data with a broken-line model estimated the TAAA requirement of red drum to be 2.10 g/100 g dry diet (1.69 g Phe + 0.41 g Tyr).