The effect of dietary methionine level on growth and on the hepatic gene expression in rainbow trout (Oncorhynchus mykiss) depends on the raw material origin Marine Rolland1,2*, Johanne Dalsgaard2, Jørgen Holm1, Pedro Gómez-Requeni1, Peter V. Skov2 1BioMar A/S, Mylius Erichsensvej 35, DK-7330 Brande, Denmark 2DTU Aqua, Section for Aquaculture, The North Sea Research Center, P.O. Box 101, DK-9850 Hirtshals, Denmark *mrol@aqua.dtu.dk INTRODUCTION Plant proteins (PP) currently used as substitutes for fish meal (FM) in aquafeeds, such as pea or soybean, are largely deficient in methionine (Met), an essential amino acid. The present study investigated the effect of i) replacing marine raw materials with pea and soy protein concentrates (PPC and SPC, respectively), and ii) supplementing with crystalline Met on growth performance and hepatic expression of genes regulating growth and amino acid catabolism. EXPERIMENTAL DESIGN RESULTS GROWTH PERFORMANCE Diets: PP vs. FM based diets containing two different Met levels (1 and 2) AMINO ACID CATABOLISM SOMATOTROPIC AXIS Best PER (FM1)  LOWEST expression of CATABOLIC enzymes Highest Met (PP2 & FM2)  apparent HIGHER capacity for amino acid CATABOLISM Rainbow trout (n=70) fed in excess for six weeks to monitor growth performance . Final sampling 24 h after the last meal to analyze hepatic gene expression (n=7). One way ANOVA tests (p<0.05) Best growth (FM1)  HIGHEST expression of IGF-I and IGF-II  PROTEIN SYNTHESIS & GROWTH. Poorest growth (PP2)  HIGHEST expression of IFGBP-Ib  LOWEST IGF-I ACTIVITY CONCLUSIONS Dietary methionine level and raw material origin affect growth performances through changes in feed intake and feed conversion ratio. The best performing fish had a reduced expression of genes coding for amino acid catabolism and an increased expression of genes coding for IGFs. The effect of dietary methionine level on gene expression differed depending on the raw material origins, likely due to differences in micro nutrient composition and DP:DE. EAS, 14th to 17th of October 2014, San Sebastian, Spain