Effects Of Dietary Carbohydrate-to-lipid Ratio On Growth, Body Composition, Non-specific Immunity And Hematological Parameters Of Largemouth Bass (Micropterus Salmoides)

An 8-week feeding trial was conducted to investigate the effect of dietary carbohydrate-to-lipid (CHO/LIP, w/w) ratios on the growth performance, body composition, non-specific immunity and hematological parameters in largemouth bass. Six iso-nitrogenous (46% crude protein) and iso-energetic (17.5 MJ/kg available energy) diets were formulated with varying CHO/LIP ratios from 0.32 to 5.17 for diets A-F respectively. Each diet was randomly assigned to four groups of 35 fish of each, which were fed by hand to apparent satiation twice daily (at 08:00 and 16:00 h). An indoor flow-through and aerated freshwater system was adapted. During the experiment period, water temperature was maintained at 28±1°C, dissolved oxygen was higher than 6mg/L, and natural light cycle was adapted.The results of this study are presented as follows:Specific growth rate (SGR) was significantly affected by dietary CHO/LIP ratios: SGR of fish fed diet with the ratio of 0.32 was significantly higher than those of fish fed diets with the other ratios.With CHO/LIP ratios increasing from 0.32 to 5.17,both ADCCP and ADCGE decreased significantly. No significant difference was observed in FCR.Viscerosomatic index (VSI) of largemouth bass fed diet with the ratio of 0.32 was significantly higher than those of fish fed diets with the other ratios. Hepatosomatic index (HSI) kept increasing as the dietary CHO/LIP ratios ranging from 0.32 to 5.17. Condition factors (K) of largemouth bass were not affected by varying CHO/LIP ratios.Lipid content of whole body decreased as dietary CHO/LIP ratios increased: the lipid content in fish fed diets A, B and C was significantly higher than in fish fed diets D and E, at the same time lipid content in fish fed diets D and E was significantly higher than in fish fed diet F. However, crude protein, moisture and ash concentrations of whole body were not significantly affected by varying CHO/LIP ratios.The protein content of liver decreased as dietary CHO/LIP ratios increased: protein content in fish fed diet A was significantly higher than in fish fed diet B, at the same time protein content in fish fed diet B was significantly higher than in fish fed diet C, D, E and F. Hepatic glycogen content kept increasing as CHO/LIP ratios increased: the difference between any groups was significant, except for between group B and group C. Lipid content of liver decreased as CHO/LIP ratios ranging from 0.32 to 5.17. No significant difference was observed in moisture content of liver. There were no significant differences in proximate composition of muscle among fish fed the different diets.Hepatic glucose-6-phosphatase activity did not present significant difference among the tested fish. Hepatic glucokinase activity was significantly lower in fish fed diet A than in fish fed the other diets, except for in fish fed diet B and C.The serum lysozyme activity of fish fed diet A was higher than that of fish fed the other diets, however no significant difference was observed in respiratory burst activity of head-kidney leukocytes, survival rates and serum classical complement pathway activity.After 6 hours of feed deprivation, plasma glucose significantly increased as CHO/LIP ratios increased, and then plasma glucose levels among the treatments all returned to basal levels after 24 hours of feed deprivation. With CHO/LIP ratios ranging from 0.32 to 5.17, hemoglobin concentration and RBC count decreased while total WBC and granulocyte counts increased. The CHO/LIP ratios failed to significantly affect lymphocyte, monocyte, thrombocyte counts and packed cell volume.