Optimal starch supplementation level in diets for juvenile mandarin fish (Siniperca chuatsi)

Mandarin fish, Siniperca chuatsi, is an economically important cultured species in China, yet its nutritional requirements remain insufficiently studied. To determine the optimal dietary starch level for all-female mandarin fish (Dinggui Ⅰ) juveniles, an 8-week feeding trial assessed the effects of graded starch inclusion on growth performance, serum biochemistry, liver histology, hepatic antioxidant capacity, and glucose metabolism. Five iso-nitrogenous and iso-lipidic diets were formulated with 7%, 10%, 13%, 16% and 19% cassava starch (S7-S19) and fed to quadruplicate groups of juveniles initial body wight, (37.8 ± 1.2) g, 12 fish per tank. With increasing dietary starch levels, the growth performance (final body weight, specific growth rate, and weight gain rate) of S. chuatsi was significantly improved with 13% starch, and then levelled off. Compared with the S7 fish, whole-body lipid level was significantly increased in the S13 fish, while liver lipid level was markedly increased in the other treatments. Increased blood glucose along with higher serum aspartate aminotransferase and alanine aminotransferase activities were recorded when dietary starch exceeded 13%. Concurrently, intensified vacuolation with nuclear aggregation and even karyolysis were associated in the liver of S. chuatsi fed with over 13% dietary starch. Compared to the S7 fish, hepatic reduced glutathione concentration was significantly decreased in the S16 and S19 fish, while total antioxidant capacity was markedly reduced in the S19 fish. The relative expression of glucose transporter 2 (glut2) in the liver was significantly down-regulated in the other treatments compared with the S7 fish. The mRNA level of g6pca1 in the liver was significantly higher in the S13 and S16 fish than in the S7 fish. Based on comprehensive evaluations of growth performance, feed utilization, liver health, and hepatic glucose metabolism, it is recommended that the starch level should be lower than 13% in the diet for S. chuatsi. These results provide key guidance for carbohydrates use in mandarin-fish feeds.