Effects of dietary carbohydrate sources on growth performance, glycogen accumulation, insulin signaling pathway and hepatic glucose metabolism in largemouth bass, Micropterus salmoides

The present study was conducted to investigate the effects of dietary carbohydrate sources, alpha-cassava-starch, potato starch, pea starch and dextrin, on growth performance, glycogen accumulation, insulin signaling pathway and hepatic glucose metabolism in largemouth bass (initial body weight 36.34 +/- 0.30 g) for 11 weeks. Results showed that pea starch significantly improved the specific growth rate (SGR), daily weight gain (DWG) and net fish yield (NFY) of largemouth bass compared to other starch, which maybe related to the depressed feed conversion ratio (FCR). Meanwhile, fish fed the diet with pea starch obtained the minimum hepatic glycogen content, which is significantly lower than that of alpha-cassava starch. The above result indicated that the fish was more tolerant to pea starch than other carbohydrate sources in accordance with the result of postprandial glucose content. The expression of insulin receptor (IR), insulin receptor substrate 1 (IRS1) and phosphoinositide 3-kinase regulatory subunit 1 (PI3KR1) was significantly up-regulated in fish fed the diet with pea starch than others, indicating the significantly higher activity of insulin pathway in the pea starch group at least at the transcription level. Meanwhile, pea starch led to a significantly increased expression of glucokinase (GK) and liver-type 6-phosphofructokinase isozyme (PFKL), while dietary starch sources had no significant influence on the expression of phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-bisphosphatase-1 (FBP1). The improved glycolysis and poor inhibited gluconeogenesis may account for the reduced hepatic glycogen content of pea starch. Therefore, pea starch was most suitable starch among the sources used for largemouth bass.