Glycemic response after glucose oral administration of wild juvenile red grouper Epinephelus morio fed two different diets

Epinephelus morio is a large carnivorous species of the Caribbean Sea under reproduction in captivity and nutritional physiology. A diet with raw cornstarch (RCS) was compared to a basal diet without starch (basal) to measure plasma glucose, liver glycogen, and intermediary metabolism. Glucose level did not change (p > 0.05) whereas liver glycogen was significantly higher in fish fed the RCS diet (137.2 ± 14.5 mg g−1) than in fish fed the basal diet (87.4 ± 14.5 mg g−1). Oral glucose administration (170 mg glucose per 100 g body weight) yielded a slight change; two peaks of plasma glucose were recorded with basal (5.6 mM L−1) 2 h after oral administration and at 12 h (6.4 mM L−1). After 24 h, with 1.7 mM L−1, fish returned to initial stage (2.4 mM L−1). RCS diet produced the highest level (6.3 mM L−1) 2 h after oral administration; lowest level observed at 24 h after oral administration (1.0 mM L−1). A significant effect was detected with the presence or absence of dietary carbohydrates (CBH) on hepatic fructose 1,6-bisphosphatase and pyruvate kinase activity. Grouper used two strategies to maintain glucose homeostasis: CBH present in the diet oriented towards gluconeogenesis, whereas no dietary CBH enhanced glycolytic route to liberate glucose and increase liver glycogen.