Effects of dietary protein, lipid and carbohydrate levels on hematological parameters, intestinal histoarchitecture and digestive enzymes activities in orange-spotted grouper (Epinephelus coioides) juveniles

A 56-day research was conducted to assess the influence of dietary protein content and carbohydrate: lipid ratio on growth performance, hematological parameters, intestinal histoarchitecture and digestive enzymes activities of orange-spotted grouper (Epinephelus coioides) juveniles (13.7 g). Four experimental diets were designed with various protein, lipid and carbohydrate levels namely LP-LCL (low protein 40%-low carbohydrate: lipid ratio=1.4), HP-LCL (high protein 48%-low carbohydrate: lipid ratio=1.4), LP-HCL (low protein 40%-high carbohydrate: lipid ratio=2.9) and HP-HCL (high protein 48%-high carbohydrate: lipid ratio=2.9). Fish were stocked into twelve 300-L cylindrical polyethylene tanks (15 fish in each tank) and fed with experimental diets. The low carbohydrate: lipid ratio diets improved growth rate of the fish. The lipid content of the whole body increased with decreasing dietary carbohydrate to lipid ratio. The intestinal folds' length and thickness significantly increased in the low carbohydrate: lipid ratio treatments. The intestinal total alkaline protease activity elevated by increasing dietary protein content, meanwhile the activities of lipase and amylase increased with increasing dietary lipid and carbohydrate levels, respectively. Blood hematocrit decreased but hemoglobin increased by increasing dietary carbohydrate to lipid ratio. According to the results dietary lipid is more preferable than carbohydrate as an energy source for orange-spotted grouper juveniles and induces protein sparing effect in a low protein content diet.