Immersion bath treatment of tilapia fry with myostatin1 prodomain does not affect tilapia growth at market size

Myostatin (MSTN), a member of the transforming growth factor-b (TGF-b) superfamily, is a potent negative regulator of skeletal muscle growth in mammalian species (Lee 2004). Recent studies have also indicated that fish MSTN negatively regulates muscle growth in fish (Xu, Wu, Zohar & Du 2003; Amali, Lin, Chen, Wang, Gong, Lee, Ko, Lu, Her, Chen & Wu 2004; Acosta, Carpio, Borroto, Gonzalez & Estrada 2005; Lee, Hu, Gong, Chen, Lu & Wu 2009; Medeiros, Phelps, Fuentes & Bradley 2009; Lee et al. 2010; Lee, Cho, Kim, Kim & Jin 2011). Because of the prominent role of MSTN in regulating muscle mass, there has been much interest in developing MSTN-based strategies to improve skeletal muscle growth in agriculturally important animal species, including fish (Tsuchida 2008).The MSTN prodomain (MSTNpro), the Nterminal part of MSTN precursor molecule, has been shown to be a potent suppressor of MSTN activity in mammalian species (Lee & McPherron 1999; Yang, Ratovitski, Brady, Solomon, Wells & Wall 2001; Matsakas, Foster, Otto, Macharia, Elashry, Feist, Graham, Foster, Yaworsky, Walsh, Dickson & Patel 2009; Hu, Chen, Sheng, Sun, Cao & Qiao 2010; Li, Zhao, Kim, Hu & Yang 2010). Fish MSTNpro also appears to suppress MSTN activity. The MSTN-1 prodomain (MSTN1pro) of the marine fish Sparus aurata suppressed MSTN activity in vitro (Rebhan & Funkenstein 2008). An increase in fibre number was observed in transgenic zebrafish overexpressing MSTN1pro (Xu et al. 2003). Recently, it was also observed that immersion bath treatment with flatfish (Paralichthys olivaceus) MSTN1pro (poMSTN1pro) expressed in an Escherichia coli system improved the growth of young juvenile rainbow trout (Lee et al. 2010), indicating the potential of fish MSTN-1 prodomain as an agent to improve the growth of commercially important aquaculture species. Similarly, immersion bath treatment of African catfish, goldfish and tilapia larvae with a soluble form of MSTN receptor (activin type IIB receptor) improved body mass growth of those fish (Carpio, Acosta, Morales, Santisteban, Sanchez & Estrada 2009). These studies, however, examined the growth response only during the 28–35 days treatment period, and did not follow the growth response to market size. Thus, it is not known whether the enhanced weight gain induced by treatment with MSTN inhibitor at the early stage of fish growth would last to later growth stages, resulting in heavier market weight when harvested at a fixed growth period. The current study was designed to address this question.