Fish growth in response to different feeding regimes and the related molecular mechanism on the changes in skeletal muscle growth in grass carp (Ctenopharyngodon idellus)

Abstract

Fish endure long periods of fasting and demonstrate an extensive capacity for rapid and complete recovery after refeeding. The aim of this study was to investigate the effects of refeeding after fasting on growth, muscle characteristics and the related gene expressions of juvenile grass carp (Ctenopharyngodon idellus). Fish were divided into three groups with triplicates: continuous feeding for 28 days (F28), 14 days of fasting and 14 days of refeeding (S14F14), and continuous fasting for 28 days (S28). Fish were sampled every 7 days for morphological, histological and gene expression analyses. Results showed that fasted fish gained weight continuously during refeeding, displaying compensatory growth. The muscle fiber diameter in S14F14 group decreased gradually during fasting and then increased with refeeding, but didn't reach the value in F28 group on 28d, while the muscle fibers density showed the opposite trend (P < 0.05). Fsih in S14F14 group recovered the intramuscular fat accumulatation during refeeding, accompanied by the upregulated expressions of fas and acc and the downregulated expressions of cpt1 and lpl in muscle on 21d. With the prolongation of fasting time, the expression of several key genes involved in myogenesis (myf5, mrf4, myog, myod, cyclind1) and muscle growth (fst, fgf6a, fgf6b) in S14F14 group decreased firstly and then increased briefly, while igf-II decreased and mstn increased continuously. All genes in S14F14 group eventually reached the same level as those in F28 group at the end of the experiment except fst and fgf6a. In conclusion, this study showed that 14 days of fasting resulted in muscle fiber atrophy in grass carp while refeeding after fasting presented compensatory mass gain, along with a coordinated regulation of several genes involved in a strong resumption of myogenesis to promote muscle growth. These results helped to understand the physiological regulation mechanism of refeeding on muscle growth of fish.