Effects of dietary carbohydrate to lipid ratios on growth performance, digestive enzyme and hepatic carbohydrate metabolic enzyme activities of large yellow croaker (Larmichthys crocea)

摘要

An 8-week feeding trial was conducted to evaluate the effect of dietary carbohydrate to lipid (CHO:L) ratios on growth performance, feed utilization, digestive enzymes and hepatic carbohydrate metabolic enzyme activities of large yellow croaker, Larmichthys crocea. Six isonitrogenous and isoenergetic diets (39.0% crude protein and 16.0 MJ kg(-1) gross energy) were formulated to contain various CHO:L ratios which ranged from 0.39 to 5.97. Triplicate groups of 50 fish (initial weight 7.06 +/- 0.48 g) were stocked in 18 floating net cages (1.5 m x 1.5 m x 2.0 m), and were fed twice daily to apparent satiation for 8 weeks. The results indicated that growth performance and feed utilization were significantly influenced by the dietary CHO:L ratios (P 0.05). Maximum weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) and feed efficiency (FE) occurred at 1.34 dietary CHO:L ratios. There were no significant differences in VSI and HSI among all treatments, however, the lowest condition factor (CF) was observed at 0.39 dietary CHO:L ratios. Moisture, protein, and ash contents of whole body were not significantly affected by the dietary CHO:L ratios (P > 0.05), and lipid content in whole body significantly decreased with dietary CHO:L ratios increasing from 0.39 to 1.69 (P > 0.05). Hepatic glycogen and muscle glycogen significantly increased with dietary CHO:L ratios from 0.39 to 1.34 then plateaued from 1.34 to 5.97. Fish fed the 0.39 CHO:L ratio diet had higher cholesterol concentration in serum than those fed the diets containing 1.69, 3.00 and 5.97 dietary CHO:L ratios; the lowest glucose concentration in serum was observed at dietary 0.39 CHO:L ratio, however, there were no significant differences in triglyceride and total protein concentrations of serum among all diets. Amylase, pepsin and lipase activities were significantly influenced by the dietary CHO:L ratios, and maximum amylase activity occurred at the 1.34 CHO:L ratios. Glucokinase (GK), pyruvate kinase (PK), and phosphoenolpyruvate carboxykinase (PEPCK) activities significantly increased with dietary CHO:L ratios increasing from 0.39 to 1.34, and then significantly decreased with further increase of dietary CHO:L ratios; no significant difference of phosphofructokinase (PFK), fructose-1,6-biphosphatase (FBPase) and glucose-6-phosphatase (G6Pase) activities was observed among all treatments. Based on weight gain, the optimal CHO:L ratio was determined to be 1.34 (approximately dietary 12.56% starch and 12.15% lipid) of dry diet for juvenile large yellow croaker.