Dietary supplementation of Lemna minor improves glycemic regulation in grass carp (Ctenopharyngodon idella).

Efficient carbohydrate utilization remains a major challenge in fish nutrition, particularly for fish fed high-carbohydrate diets. Lemna minor (duckweed), a plant rich in bioactive compounds including flavonoids and polyphenols, has potential as a functional feed ingredient to enhance glucose metabolism. In this study, grass carp were fed diets supplemented with Lemna minor at 2%, 6%, and 10% inclusion levels, alongside positive and negative control diets. Postprandial responses were monitored over 12 h, assessing digestive enzyme activities (amylase, glucokinase, pyruvate kinase), glucose transporter expression (GLUT2), plasma metabolites (glucose, insulin), and hepatic metabolic markers, including glycolytic (Glucokinase and Pyruvate kinase) and gluconeogenic enzymes (G6Pase, FBPase, PEPCK) and glycogen content. Dietary L. minor significantly accelerated digestive enzymes, with amylase activity peaking at 3 h post-feeding compared to delayed 6-h peaks in controls. GLUT2 expression upregulated in parallel, supporting enhanced glucose absorption. Hepatic glucokinase and pyruvate kinase activities were elevated in LM-fed groups, with LM10% demonstrating the highest responses. Correspondingly, plasma glucose was faster, with normoglycemia achieved by 6 h in the LM10% group, whereas controls exhibited prolonged hyperglycemia. Insulin secretion was robust and sustained in Lemna-fed groups (3-9 h), contrasting with inadequate responses in controls. Hepatic G6Pase activity and gene expression were downregulated by LM-fed fish, indicating reduced gluconeogenesis, while glycogen storage was enhanced. These results indicate that Lemna minor improves postprandial carbohydrate metabolism in grass carp through coordinated modulation of digestive enzyme activity, glucose transport, insulin response, and hepatic metabolic pathways. The present study concluded that 10% inclusion level provided optimal metabolic benefits, highlighting the potential of Lemna minor as a sustainable, bioactive feed additive to enhance carbohydrate utilization in herbivorous aquaculture species.