Myosin heavy chain mRNA expression correlates higher with muscle protein accretion than growth in Atlantic salmon, Salmo salar E.M. Hevrøy a, * , A-E.O. Jordal a , I. Hordvik a,b , M. Espe a , G-I. Hemre a , P.A. Olsvik a a National Institute of Nutrition and Seafood Research (NIFES), PO Box 2029, Nordnes, N-5817 Bergen, Norway b University of Bergen, Department of Biology, HiB, N-5020 Bergen, Norway Received 1 April 2005; received in revised form 8 July 2005; accepted 11 July 2005 Abstract In order to link growth and protein accretion in Atlantic salmon the mRNA expression of muscle myosin heavy chain (MyHC) was analysed. MyHC gene is expressed throughout muscle development and is consistent with the hypertropic growth in fish. Total RNA was isolated from white muscle tissues (N = 32) from salmon fed a fish meal based diet with three levels of solubilised protein incorporated as fish protein hydrolysate (FPH) control (0 g kg À 1 ), medium (180 g kg À 1 ) and high (300 g kg À 1 ) FPH inclusion. The salmon were PIT-tagged and fed the experimental diets for a period of 68 days. A high level of dietary FPH resulted in significant up-regulation of MyHC by a factor of 2.4 compared to fish fed the medium FPH inclusion. The fish with highest MyHC expression also contained significant higher levels of muscle protein. MyHC expression correlated higher with protein accretion than individual specific growth rate (SGR) in salmon. These observations indicate that MyHC mRNA expression can be a useful marker for understanding of growth and protein accretion in Atlantic salmon. D 2005 Elsevier B.V. All rights reserved. Keywords: Myosin heavy chain (MyHC); White muscle; Solubilised protein; FPH; Atlantic salmon 1. Introduction In fish nutrition studies performed in tanks or cages with large numbers of individuals it is difficult to control individual feed intake and give individual estimates on protein accretion. Growth is thought to have a close relationship with protein accretion (Carter et al., 2001), and there is a need for increased knowledge on the physiological regulation of muscular growth. One possible candidate linking growth and protein accretion is the myosin heavy chain (MyHC) gene which is present throughout muscle development in fish (Gauvry and Faucon- neau, 1996). During growth, when white muscle fibers in fish increase in size (hypertrophic growth), the growth in body girth relies also on new muscle fiber recruitment (hyperplasia), but is largely driven 0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.07.003 * Corresponding author. Tel.: +47 55905146; fax: +55905299. E-mail address: ernst.hevroy@nifes.no (E.M. Hevrøy). Aquaculture 252 (2006) 453 – 461 www.elsevier.com/locate/aqua-online