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Keywords
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Dietary macronutrients, Digestive enzymes, Enterocytes, Grouper, Growth,
Hematology
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Abstract
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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.
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