Apparent protein digestibility (APD)
The apparent protein digestibility (APD) was calculated as follows [21]:
APD=1−(F/D×Di/Fi),
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where D = % crude protein of diet, F = % crude protein of faeces, Di = % digestion indicator (AIA) of diet, and Fi = % digestion indicator (AIA) of faeces.
Serum analysis
Five blood samples/replicate were collected using clean syringes from the caudal vessels of fish at the termination of the experiment. The blood samples were centrifuged at 1500g for 15 min at 4 °C. The sera were used for the determination of serum transaminases, alanine aminotransferase ALT and aspartate aminotransferase AST [22], urea [23], creatinine [24] and blood urea nitrogen (BUN) [25]