The characteristics of glucose homoeostasis in grass carp and Chinese longsnout catfish after oral starch administration: a comparative study between herbivorous and carnivorous species of fish

An oral starch administration trial was used to evaluate glucose homoeostasis in grass carp (Ctenopharyngodon idella) and Chinese longsnout catfish (Leiocassis longirostris Günther). Fish were administered with 3 g of a water and starch mixture (with 3:2 ratio) per 100 g body weight after fasting for 48 h. Fish were sampled at 0, 1, 3, 6, 12, 24 and 48 h after oral starch administration. In grass carp, plasma levels of glucose peaked at 3 h but returned to baseline at 6 h. However, in Chinese longsnout catfish, plasma glucose levels peaked at 6 h and returned to baseline at 48 h. The activity of intestinal amylase was increased in grass carp at 1 and 3 h, but no significant change in Chinese longsnout catfish was observed. The activity of hepatic glucose-6-phosphatase fell significantly in grass carp but change was not evident in Chinese longsnout catfish. The expression levels and enzymic activity of hepatic pyruvate kinase increased in grass carp, but no significant changes were observed in the Chinese longsnout catfish. Glycogen synthase (gys) and glycogen phosphorylase (gp) were induced in grass carp. However, there was no significant change in gys and a clear down-regulation of gp in Chinese longsnout catfish. In brief, compared with Chinese longsnout catfish, grass carp exhibited a rapid increase and faster clearance rate of plasma glucose. This effect was closely related to significantly enhanced levels of digestion, glycolysis, glycogen metabolism and glucose-induced lipogenesis in grass carp, as well as the inhibition of gluconeogenesis.