The dietary tryptophan requirement of juvenile red drum, Sciaenops ocellatus
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2016 Elsevier B.V. The red drum, Sciaenops ocellatus, is cultured in the United States for both stock enhancement and food production. Several amino acid requirements of this species have been quantified but not tryptophan. Therefore, two feeding trials were conducted in a brackish water (7ppt) recirculating culture system consisting of 38-L aquaria to determine the optimum dietary tryptophan requirement of juvenile red drum. In feeding trial 1, six semi-purified diets composed of red drum muscle and crystalline amino acids to contain 35% crude protein were supplemented with incremental levels of tryptophan ranging from 0.14 to 0.64% of dry diet. Each diet was fed to triplicate groups of fish for 7weeks. Red drum fed the basal diet without adequate tryptophan exhibited significantly (P0.05) reduced weight gain, feed efficiency, body condition indices and survival compared to fish fed the other diets. Fish fed all diets containing tryptophan from 0.24 to 0.64% had similar growth performance. Thus, a second trial was conducted with a narrower range of tryptophan inclusion levels to estimate a more refined requirement. In this second trial, five experimental diets were prepared by supplementing incremental levels of tryptophan ranging from 0.14 to 0.34% of dry weight. Once again, weight gain, feed efficiency, protein efficiency ratio and body condition indices were significantly reduced in fish fed the basal diet after 7weeks. Based on a quadratic broken-line regression model and using weight gain as the response criterion, the minimum dietary tryptophan requirement of red drum was determined to be 0.280.05% of dry diet (0.80% of dietary protein). Statement of Relevance This study quantified the dietary tryptophan requirement of red drum. Such information can be used to insure the tryptophan requirement of the fish is met while using a greater variety of dietary protein feedstuffs.
