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Response of Rainbow Trout (Oncorhynchus mykiss) Growing from 50 to 150 g to Supplements of DL-Methionine in a Semipurified Diet Containing Low or High Levels of Cystine^1,2,3,

Institut für Tierernährung der Universität Bonn, D-53115 Bonn, Germany ^* Degussa AG, Applied Technology Feed Additives, D-63403 Hanau, Germany

We studied the effect of increasing dietary concentrations of DL-methionine on growth, feed intake, feed conversion ratio and the composition of gain in rainbow trout. Twenty-four groups of 20 trout initially weighing 51 ± 0.5 g/trout were fed semipurified diets containing 20.1 MJ digestible energy and either 3.0 or 5.8 g cystine/kg dry matter. At each level of cystine, 12 levels of methionine (2 to 11 g/kg dry matter) were achieved by supplementation with graded quantities of DL-methionine. During an experiment of 49 feeding days, no significant effect of the level of dietary cystine was found for any performance trait. Nonlinear responses to increasing dietary methionine concentrations were found for feed intake, growth rate, protein concentration of gain and protein deposition, whereas fat concentration of gain decreased concurrently. Dietary methionine was utilized most efficiently at a concentration of 3.5 g methionine/kg dry matter or 0.17 g/MJ digestible energy. Ninety-five percent of the plateau deposition of body protein was achieved at a dietary methionine concentration of 8 g/kg dry matter or 0.40 g/MJ digestible energy. For achieving 98%, the required concentration was 9.0 g/kg or 0.49 g/MJ. Recommended dietary methionine concentration will depend on the trait chosen.

KEY WORDS: • methionine • rainbow trout • requirement • cystine

¹ Presented in part at the EIFAC Workshop on Methodology for Determination of Nutrient Requirements in Fish, June 29–July 1, 1993, Eichenau, Germany [Pack, M., Rodehutscord, M., Jacobs, S. & Pfeffer, E. (1993) Amino acid requirement of rainbow trout (Oncorhynchus mykiss). 2. Protein deposition as function of dietary methionine, threonine and arginine.].

² With the financial support of the Deutsche Forschungsgemeinschaft.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 30 November 1993. Revision accepted 23 August 1994.