Ploidy effects on genes regulating growth mechanisms during fasting and refeeding in juvenile rainbow trout (Oncorhynchus mykiss)

•Diploids mobilized visceral nutrient stores more than triploids during fasting.•Carcass growth rate recovered more quickly in the triploids during refeeding.•Decreased igfbp expression may contribute to improved recovery growth in triploids.•Liver ghr2 and igfbp2b expression increased and igfbp1b decreased in fasted fish. Diploid and triploid rainbow trout weighing approximately 3g were either fed for five weeks, or feed deprived for one week, followed by refeeding. During feed deprivation gastrointestinal somatic index decreased in diploids, but not triploids, and during refeeding, carcass growth rate recovered more quickly in triploids. Although not affected by ploidy, liver ghr2 and igfbp2b expression increased and igfbp1b decreased in fasted fish. Effects of ploidy on gene expression indicate potential mechanisms associated with improved recovery growth in triploids, which include decreased hepatic igfbp expression, which could influence IGF-I bioavailability, differences in tissue sensitivity to TGFbeta ligands due to altered tgfbr and smad expression, and differences in expression of muscle regulatory genes (myf5, mstn1a, and mstn1b). These data suggest that polyploidy influences the expression of genes critical to muscle development and general growth regulation, which may explain why triploid fish recover from nutritional insult better than diploid fish.