Effect of overwintering on body composition, antioxidant enzyme activities, fatty acid composition, glucose and lipid-metabolic related gene expression of grass carp (Ctenopharyngodon idellus)

Abstract

During overwintering in aquaculture, fish are subjected to the coordinated stress of low temperature and starvation. This study investigates the physiological strategies in response to overwintering in grass carp, including glucose and lipid utilization. Grass carp were sampled at 0, 8, and 16 weeks of overwintering. Then, body composition, antioxidant enzyme activities, fatty acid composition, as well as glucose and lipid metabolic gene expression were determined in hepatopancreas, muscle, and adipose tissue. The results indicated that the three tissues exhibited distinct glucose and lipid metabolisms during overwintering. During overwintering, lipolysis was activated in adipose tissue through influencing ATGL gene expression. In hepatopancreas, triglycerides were also utilized during overwintering; starvation of 8 weeks significantly increased the glycogen content via gluconeogenesis activation, but the glycogen content remained steady from the 8th to the 16th week. The muscle firstly utilized glycogen via glycolysis, followed by triglycerides as energy substrates. Interestingly, starvation of 8 weeks significantly increased the triglycerides content of muscle, which may be dependent on LPL-mediated lipid transport mechanism. Hence, during overwintering, glucose was used mainly during the early stage, and muscle was the main utilization site, while lipids were utilized during the whole stage. According to the results indicating that lipids were continuously utilized as energy substrates, antioxidant enzyme activities demonstrated that adipose tissue is one of the most vulnerable tissues to oxidative stress. In addition, principal component analysis (PCA) of fatty acid composition indicated that SFA was the predominant fatty acid used by grass carp during overwintering. Our results provide critical fundamental information for understanding the physiological responses to overwintering stress and development of nutritional feed before and after overwintering in grass carp.