Dietary protein requirement of the high altitude's representative teleost juveniles Schizopygopsis younghusbandi (Cypriniformes: Cyprinidae)

A 60-day trial was conducted to investigate the effect of dietary protein on growth, whole-body composition, hepatopancreas enzymes, digestion and absorption in the juveniles of Schizopygopsis younghusbandi. Six graded levels of dietary protein (200.0, 248.7, 303.5, 351.2, 395.8 and 449.3 g/kg diet) were formulated and assigned to triplicate groups of 60 fish (8.16 +/- 0.02) for each aquarium. Results showed a significantly increased specific growth rate (SGR) in fish fed protein containing 351.2 g/kg diet (p < .05). Besides, intestinal ratio (IR), intestinal somatic index (ISI) and hepatosomatic index (HSI) were decreased and the condition factor (CF) was increased with dietary protein up to 351.2 g/kg diet, then altered reversely. Fish fed the optimal dietary protein showed the highest crude protein calcium, phosphorous and lowest crude lipid contents of the whole body in fish. Additionally, plasma ammonia content (PAC), and activities of GOT and GPT were enhanced by dietary protein levels (p < .05). The digestive enzymes of hepatopancreas were generally increased with the quadratic response to dietary protein levels. Optimal dietary protein level increased the intestinal enzyme activities of Na+, K+-ATPase (NKA), alkaline phosphatase (AKP), gamma-glutamyl transpeptidase (gamma-GT) and creatine kinase (CK). Based on the 2-slope broken-line model analysis of PWG, dietary protein requirement was determined to be 349.6 g/kg diet.