Effects of dietary carbohydrate to lipid levels on growth performance and carbohydrate metabolism of juvenile Chinese sucker, Myxocyprinus asiaticus

【Objective】This study investigated the influences of dietary carbohydrate-to-lipid m(CHO)∶m(L) on growth performance, feed utilization and carbohydrate metabolism enzymes activities of juvenile Chinese sucker,Myxocyprinus asiaticus to detect the suitable addition proportion of m(CHO)∶m(L) to the diet of juvenile Chinese sucker.【Method】Six isonitrogenous (crude protein 41%) and isoenergetic (16 kJ/g) diets were formulated to contain with graded levels of m(CHO)∶m(L) (0.29,0.81,1.58,2.88,5.46 and 13.22). Each diet was randomly fed to one treatment of Chinese sucker with an average initial body mass of (4.01±0.02) g for 8 weeks. Mass gain rate(MGR), specific growth rate (SGR), body composition and carbohydrate metabolism enzymes activities of juvenile Chinese sucker were detected and analyzed.【Result and conclusion】The mass gain rate and specific growth rate increased initially but then decreased with the increasing dietary m(CHO)∶m(L), thus reaching the highest in fish fed diets with m(CHO)∶m(L) of 5.46, which was significantly higher than those of fish fed other diets (P<0.05), whereas feed coefficient rates(FCR) showed a converse trend; the crude lipid content in whole body of fish decreased with the increasing dietary m(CHO)∶m(L) significantly (P<0.05), while hepatic crude lipid decreased initially and then increased, reaching the lowest level in fish fed diets with m(CHO)∶m(L) of 2.88; Hepatic triglycercide concentrations increased significantly with the increasing dietary m(CHO)∶m(L) (P<0.05), while activities of aspartate aminotransferase(AST) and alanine aminotransferase(ALT) increased initially and then decreased, reaching the peak with dietary m(CHO)∶m(L) of 2.88; lipid content of muscle was lowest in fish fed diet with m(CHO)∶m(L) of 13.22, which was significantly lower than in fish fed diet with m(CHO)∶m(L) of 0.29 (P<0.05). Hepatic pyruvate kinase(PK) activities increased significantly with the increasing dietary m(CHO)∶m(L) (P<0.05), while phosphoenolpyruvate carboxykinase(PEPCK) showed a converse trend. No significant difference was observed in activities of hepatic hexokinase(HK) and glucose-6-phosphatase(G-6-pase) among dietary treatments (P>0.05). Based on broken-line regression analysis of SGR against dietary m(CHO)∶m(L), a m(CHO)∶m(L) of 465 was proved to be optimal for the growth of juvenile Chinese sucker.