Dietary starch levels modulate growth performance, glucose utilization, and lipogenesis in mandarin fish (Siniperca...

The study investigated how varying levels of dietary starch influence the growth, health status, and glucose-lipid metabolism of mandarin fish (initial body weight: 106 ± 1 g). Five diets containing graded levels of digestive starch were formulated (6.56%, 9.03%, 13.03%, 16.46%, and 19.57%), designated as D6.56, D9.03, D13.03, D16.46, and D19.57, respectively. Each diet was administered to triplicate groups of mandarin fish twice daily over 8 weeks. Results showed that growth performance increased linearly, peaking in the D13.03 group starch level before declining (P < 0.05). Liver and muscle lipid content and hepatic glycogen increased significantly in a quadratic and linear manner, respectively (P < 0.05). Transcriptional analysis revealed a starch-dependent upregulation of insulin signaling (ira, pi3kr1, and akt1) and glycolysis (gk, pfkl, and pk) genes, with concurrent downregulation of gluconeogenesis (fbp1 and g6pc) (P < 0.05). Protein expression analysis showed the ratio of p-PI3KR1 to PI3KR1 was significantly elevated as dietary starch increased, with the D13.03 group showing higher ratios than the D19.57 group (P < 0.05). FoxO1 expression was decreased in high-starch groups and reached a peak in the D13.03 group, while the phosphorylation of FoxO1 was significantly elevated (P < 0.05). Additionally, ChREBP and SREBP-1 protein levels were elevated in the D13.03 and D19.57 groups compared to the D6.56 groups (P < 0.05). In conclusion, mandarin fish showed superior carbohydrate tolerance with optimal growth at 13.03% dietary starch, which was partly due to the superior capacity to convert carbohydrates into triglycerides.