Determining the Dietary Tryptophan Requirement of Juvenile Red Drum

Abstract

ABSTRACT The Dietary Tryptophan Requirement of Juvenile Red Drum. (May 2015)

Emily Pewitt Department of Wildlife and Fisheries Sciences Texas A&M University

Research Advisor: Dr. Delbert M. Gatlin III Department of Wildlife and Fisheries Sciences

The red drum, Sciaenops ocellatus, is cultured in the United States for both stock enhancement and food production. Ongoing studies in this laboratory are quantifying optimum dietary levels of indispensable and dispensable amino acids of red drum in order to compile a complete set of nutritional requirements. The present study was conducted to determine the optimum dietary tryptophan requirement of red drum. Groups of twelve red drum fingerlings, of initial average weight of 1.5- 2.5 g each were placed into each of 28, 38-L aquaria containing brackish water (7ppt) prepared from well water and a mixture of stock salt and commercial synthetic seawater. Seven semi-purified diets composed of red drum muscle and crystalline amino acids were supplemented with incremental levels of tryptophan. Each diet was given to triplicate groups of fish which were weighed every week to observe health and growth as influenced by dietary tryptophan. Water quality samples were also observed multiple times per week. At the end of the 39-day feeding period, the optimal tryptophan requirement of red drum was estimated based on weight gain, feed efficiency and protein conversion efficiency. Red drum fed the basal diet without adequate tryptophan exhibited significantly (P< 0.05) reduced weight gain, feed efficiency and survival compared to fish fed the other diets. However, no other specific signs of deficiency were observed. All of the diets supplemented with tryptophan from 0.25 to 0.75% supported similar growth performance. Based on these data, the minimum dietary tryptophan requirement of red drum was determined to be 0.25% of dry diet. This information can be used in formulating diets for red drum to ensure adequate levels of tryptophan are provided.