Expression of selenoprotein genes in muscle is crucial for the growth of rainbow trout (Oncorhynchus mykiss) fed diets supplemented with selenium yeast

Selenium (Se) is an essential trace element for fish growth and performs its physiological functions mainly through incorporating into selenoproteins . It is well known that dietary Se regulates fish growth by controlling the synthesis of deiodinase , a kind of selenoproteins. However, recently, as many as 41 selenoproteins have been characterized in teleost fish. We propose a hypothesis if other selenoproteins, besides deiodinase, could also involve in the regulation of fish growth. In the present study, rainbow trout ( Oncorhynchus mykiss ) were fed diets supplemented with or without graded levels of Se (2, 4 or 6 mg/kg, from selenium yeast, Se-yeast) for 10 weeks. At the end of the feeding trial, fish growth and the expressions of a total of 28 selenoprotein genes in tissues have been evaluated. Results showed that dietary Se-yeast supplementation significantly increased fish growth ( P  < 0.05) without causing oxidative stress in fish tissues. In addition, dietary Se supplementation caused a general up-regulation of selenoprotein gene expressions either in liver (10 genes) or in muscle (11 genes) ( P  < 0.05). Correlation analysis showed that rainbow trout growth was significantly and positively correlated to only 4 selenoprotein genes in liver but all the 11 differentially expressed selenoprotein genes in muscle ( P  < 0.05), and it presented the strongest correlation with the mRNA levels of muscle selenoprotein W-like gene ( P  < 0.05). These results indicate that dietary Se-yeast supplementation is beneficial for rainbow trout growth, and the enhanced growth performance is closely correlated to the expressions of muscle selenoprotein genes, particularly the selenoprotein W-like gene. This study reveals the importance of muscle selenoprotein gene expressions, and provides a new concept for the regulatory mechanism of dietary Se on fish growth.