Expression of growth-related genes in muscle during fasting and refeeding of juvenile Atlantic halibut, Hippoglossushippoglossus L.

The aim of this study was to establish a fasting–refeeding protocol to investigate the expression of growth-related genes during the transition between catabolic and anabolic states in Atlantic halibut (Hippoglossus hippoglossus L.). Juveniles of ~ 950 g were maintained at ambient temperature (5–8 °C) until the 1st of May, then fasted for two months and refed for two months at 7.7–8.0 °C under continuous low light. Fast epaxial myotomal muscle was sampled at − 64 d (days), − 38 d, 0 d (start of refeeding), 3 d, 7 d, 14 d, 30 d and 60 d. Average body mass was unchanged over the fasting period but increased by 24.4% following 60 d refeeding. qPCR was used to analyse the stability of expression of five potential reference genes (Eef2, Fau, 18SrRNA, Actb and Tubb2) with GeNorm and Normfinder. Expression of the growth-related genes, cathepsinB (ctsb), cathepsinD (ctsd), insulin-likegrowthfactor-IandII (IGF-I and II) and insulin-likegrowthfactor-Ireceptor1a (IGF-IRa) was normalised using the geometric average of the two most stable housekeeping genes, Fau and 18SrRNA. IGF-I mRNA showed a transient 2.6-fold increase in abundance with refeeding at 7 d whilst transcripts for IGF-II and IGF-IRa were elevated during fasting and decreased 3.8-fold and 3-fold between the 0 d and 3 d samples respectively. Ctsb expression increased between − 64 d and 0 d and then decreased ~ 10-fold by 14 d refeeding. In contrast, ctsd was relatively unaffected by the fasting–refeeding cycle, showing a modest (~ 35%) transient decrease in expression between the 0 d and 30 d refeeding samples. It was concluded that the experimental protocol adopted and housekeeping genes identified were suitable for investigating the catabolic–anabolic transition in halibut skeletal muscle.