Effects of Dietary Carbohydrate/Lipid Ratios on Growth, Feed Utilization, Hematology Parameters, and Intestinal Digestive Enzyme Activities of Juvenile Hybrid Grouper (Brown-Marbled Grouper Epinephelus fuscoguttatus f x Giant Grouper E-lanceolatus o)

An 8-week growth trial was conducted to investigate the effects of dietary carbohydrate (CHO)/lipid (L) ratios on growth, feed utilization, hematology parameters, and intestinal digestive enzyme activities of juvenile hybrid grouper (Brown-marbled Grouper Epinephelus fuscoguttatus fxGiant Grouper E. lanceolatus o). Seven isoproteic (53.5% dietary crude protein) and isoenergetic (3.6kcal/g dry matter) experimental diets were formulated containing various CHO/L ratios: 0.03 (0.5% CHO/16% L); 0.36 (5% CHO/14% L); 0.79 (9.5% CHO/12% L); 1.4 (14% CHO/10% L); 2.31 (18.5% CHO/8% L); 3.83 (23% CHO/6% L); and 6.88 (27.5% CHO/4% L). Fifteen juvenile hybrid grouper (average initial body weight +/- SE=10.16 +/- 0.16g) were stocked in small floating cages. Triplicate groups of fish were fed each dietary treatment to apparent satiation twice daily (0800 and 1600hours). Results showed that weight gain (WG; %), daily feed intake (DFI), feed conversion ratio (FCR), and protein efficiency ratio (PER) were significantly affected by different experimental diet treatments. Fish that were fed diets with CHO/L ratios of 3.83 and 6.88 had lower WG and PER but higher DFI and FCR than fish that received diets with other CHO/L ratios. Intraperitoneal fat ratio and whole-body lipid content significantly decreased with increasing dietary CHO/L ratios. Hepatic glycogen content increased with increases in dietary digestible CHO level. Fish that received lower CHO/L ratios had lower plasma glucose concentrations than fish that were fed diets with higher CHO/L ratios. As dietary CHO/L ratio increased, intestinal lipase activity decreased, but intestinal -amylase activity increased. In conclusion, dietary energy from lipid could be partially replaced by that from digestible CHO without significant negative effects on growth performance of hybrid grouper. Furthermore, partial replacement of dietary lipid by CHO was beneficial for reducing fish adiposity through avoiding excessive lipid deposition in the abdominal cavity as well as in other tissues. We recommend 2.31 as a suitable dietary CHO/L ratio for hybrid grouper, since higher ratios (3.83 and 6.68) depressed fish growth performance.