Effects of dietary carbohydrate levels on growth performance, body composition, glucose/lipid metabolism and insulin signaling pathway in abalone Haliotis discus hannai

Abstract

The present study investigated the effects of different dietary carbohydrate levels on the growth performance, body composition, glucose/lipid metabolism and insulin signaling pathway in abalone Haliotis discus hannai. Eight experimental diets with graded levels of carbohydrates (18.08%, 22.10%, 26.10%, 29.90%, 34.00%, 38.01%, 41.98% and 45.55%, named as T1, T2, T3, T4, T5, T6, T7 and T8, respectively) were designed to feed abalone (initial weight 22.52 ± 0.05 g) for 110 days. The results showed that the diet containing 38.01% carbohydrate significantly increased the survival rate (SR) and weight gain rate (WGR) of abalone (P < 0.05). Based on the quadratic regression mode of WGR, the optimal dietary carbohydrate level for abalone was estimated to be 37.05%. The activities of intestinal digestive enzymes were significantly increased in the T6 group. Moreover, the expressions of pyruvate kinase (pk) and glucose-6-phosphate dehydrogenase (g6pdh) in digestive glands were up-regulated with the increase of carbohydrate content in diets, while the expression of hexokinase (hk) reached the maximum in the T6 group. The highest expressions of phosphoenolpyruvate carboxykinase (pepck), glucose-6-phosphatase (g6pase) and insulin signaling pathway related genes were found in the T6 group. The expressions of key genes related to lipolysis reached the highest in the T6 group, and then down-regulated with the further increasing dietary carbohydrate levels. The expression of key genes of lipogenesis was up-regulated with the increasing dietary carbohydrate levels. In conclusion, 38.01% of dietary carbohydrate level improved the growth performance of abalone. Dietary carbohydrate levels influenced the glucose and lipid metabolism including insulin signaling pathway. Abalone potentially had the capability to deal with a high-carbohydrate load (45.55%) by increasing glycolysis and decreasing gluconeogenesis. Meanwhile, it promoted lipid synthesis and inhibited lipolysis under high dietary carbohydrate load.