Effects of mulberry leaf extract on growth, digestion, liver lipid metabolism and hypoglycaemic ability in mandarin fish (Siniperca chuatsi)

This study aimed to evaluate the effects of mulberry leaf extract (MLE) on the digestive system, liver lipid metabolism, and hypoglycemic capacity of Siniperca chuatsi. The control group (D1) was fed basal diet without MLE, while the treatment groups received MLE supplementation at 2.5 g/kg (D2), 5.0 g/kg (D3), 7.5 g/kg (D4), and 10.0 g/kg (D5). A total of 225 Siniperca chuatsi of initial body weight (47.82 ± 0.19 g) were selected and fed for 8 weeks. The results indicated that weight gain rate (WGR), feed intake (FI), and feed efficiency (FE) initially increased and subsequently decreased with MLE supplementation, peaking in the 7.5 g/kg MLE group (D4) (P < 0.05). The highest activities of digestive enzymes in the stomach, intestine, and pyloric caecum also exhibited in this group (P < 0.05). The intestinal villi height, branching of villi, density of goblet cells significantly increased, and reduced cavity rate in the D4 group (P < 0.05). The diversity of intestinal flora, as assessed by the Chao1, Simpson, and Shannon indices, was significantly greater in this group (P < 0.05). Liver lipid metabolism indices, including CPT-1 and the CPT-1/ACC ratio, were highest in the D4 group, while the crude lipid content displayed inverse trend (P < 0.05). Additionally, the D4 group showed a reduced number of liver lipid droplets and improved antioxidant capacity, with liver cells exhibiting less swelling and vacuolation. Notably, the D4 group demonstrated a significantly better hypoglycemic response after glucose injection compared to the control group (D1). The study concludes that MLE, when incorporated at an optimal level of 6.71–6.75 g/kg, significantly enhances the structure and function of the gastrointestinal tract, pyloric caecum, and liver, stimulates liver lipid metabolism, improves hypoglycemic capacity, and promotes the growth of Siniperca chuatsi.