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Factors Affecting Dietary Requirement and Deficiency Signs of L-Tryptophan in Rainbow Trout¹

Tunison Laboratory of Fish Nutrition, U.S. Fish and Wildlife Service, 28 Gracie Road, Cortland, NY 13045

Two experiments were conducted to determine the concentration of dietary tryptophan needed for optimal growth and survival of fingerling rainbow trout (Salmo gairdneri), to characterize signs of tryptophan deficiency, and to ascertain the effects of niacin on deficiency signs. Test diets containing either hydrolyzed or intact casein were fed with graded levels of added L-tryptophan (0.0, 0.25, 0.50, 0.75 and 1.0 g/100 g protein). Maximum growth occurred at 0.75 and 0.50 g tryptophan in fish fed hydrolyzed and intact casein, respectively. Changes in mineral and amino acid mixtures in the intact casein diet yielded a cation-anion (Na + K - Cl) balance of + 15.3 meq/100 g diet and pH of 6.44, compared with a balance of -21.3 and -25 meq, and pH 5.8 and 4.4 for unmodified hydrolyzed and intact casein diets, respectively. Analysis of growth by the polynomial regression function; Y = 0.16 + 0.429X - 0.26X², where Y = mean daily gain in grams, and X = grams of added tryptophan/100 g protein, predicted that at least 0.58 g of tryptophan was needed for maximum weight gain. Analysis of apparent pathology-free fish by the function; Y = 34.33 + 147.33X = 83.87X², where Y = percentage with no signs of deficiency, and X = grams of added tryptophan, predicted that 0.63 g tryptophan/100 g protein was needed for optimum health scores. Deletion of supplemental niacin did not affect fish response to tryptophan.

KEY WORDS: • rainbow trout • tryptophan • requirement • scoliosis • cataracts

¹ Presented in part at the Fourth Joint Meeting of the American Institute on Nutrition, The American Society for Clinical Nutrition and The Canadian Society for Nutritional Sciences, The Pennsylvania State University, University Park, PA, July 23, 1982: Poston, H. A. & Rumsey, G. L. (1982) Tryptophan requirement of rainbow trout. J. Nutr. 112 (6): xxvi, 1982.

Manuscript received 8 April 1983.