The main regulator of muscle growth in vertebrates is the growth hormone (GH)-insulin-like growth factor (IGF) system (Glass, 2003, 2005; Velloso, 2008; Wood et al., 2005). In mammals,the role of this system and its signaling pathways in muscle mass accretion has been established in considerable detail (Glass, 2003,2005; Velloso, 2008), whereas in teleost fish, knowledge of the molecular regulatory mechanisms is limited.