Effect of Feeding Strategy and Carbohydrate Source on Carbohydrate Utilization by Grass Carp (Ctenopharyngodon idella)

Problem statement: Feeding strategy is the important factor in aquaculture. Feeding strategy not only could affect the growth performance of grass carp and feed efficiency, but also could affect the quality and environment of water resource. We have proved that glucose was more suitable than starch as the carbohydrate source for grass carp under the restricted feeding frequency. While different feeding strategies may have resulted in the differences in carbohydrate utilization among fish species. No studies have so far been reported that compare the utilization of carbohydrate source in different feeding strategy of grass carp. Approach: A 9-weeks growth trial was conducted to determine the effect of feeding frequency (2, 6, 12 and 23 meals day^-1) and two different carbohydrate source (30% starch versus 30% glucose) on the carbohydrate utilization of grass carp (Ctenopharyngodon idella). Both of the two diets with the same feeding rates but with four different feeding frequencies were fed to triplicate groups of grass carp (mean initial wet weight 35.94±1.86 g). Results: In the glucose diet groups, significantly (p<0.05) higher Final Body Weight (FBW, g), Weight Gain (WG, %), Specific Growth rate (SGR, % day^-1), Feed Efficiency (FE, %), Protein Efficiency Ratio (PER), body lipid and serum Triglyceride (serum TG) were observed in the 6, 12 and 23 meals day^-1 feeding treatments than that in 2 meals day^-1 feeding treatment, all these indexes were not significantly different among the 6, 12 and 23 meals day^-1 feeding treatments. While in the starch diet groups, FBW, WG and SGR of fish only in the 6 meals day^-1 feeding treatment were significantly (p<0.05) higher than that of fish in the 2 meals day^-1 feeding treatment and FBW, WG and SGR of fish in the 12 and 23 meals day^-1 feeding treatments provided intermediate results and were not significantly different from the 2 and 6 meals day^-1 feeding treatments. When compared the effects between the glucose and starch diet groups in the same feeding frequency, significantly (p<0.05) higher FBW, WG, SGR, FE and PER were observed in the glucose than the starch fed grass carp, only body lipid content was significantly higher in grass carp fed the starch than the glucose diets. Conclusion: It suggested that 6 meals day^-1 feeding was sufficient for the optimal growth and feed efficiency for grass carp on 35.1-37.5 g. Furthermore, the growth performance also suggested that glucose was superior to starch as the carbohydrate source for grass carp under the feeding frequency of 6, 12 and 23 meals day^-1.