Effect of feeding level on growth, digestive and metabolic enzymes and antioxidant capacity in juvenile Yangtze sturgeon (Acipenser dabryanus)

This study was performed to evaluate the effects of different feeding levels on the growth performance, digestive enzymes, body composition, metabolic enzymes and antioxidant activities of juvenile Yangtze sturgeon (Acipenser dabryanus). A total number of 135 fish (average initial weight of 67.80 ± 0.19 g) were randomly distributed into nine round fibre-reinforced plastic tanks with 15 fish per tank and three tanks for treatment. Fish were fed with three feeding levels [1%, 3% and 5% body weight per day (BW day−1)] twice per day for 8 weeks. The weight gain rate (WGR) and specific growth rate (SGR) in 3% BW day−1 treatment were significantly higher and the feed conversion ratio (FCR) was significantly lower than those in the other treatments (P < 0.05). The activities of amylase and lipase were significantly increased with increasing feeding levels, and fish fed with 3% BW day−1 had significantly higher trypsin activities (P < 0.05). The hepatic glucogen contents significantly increased with increasing feeding levels, and the highest glucogen levels in the muscles were found in 3% BW day−1 treatment (P < 0.05). The enzymes activites of liver metabolism significantly differed among fish fed with different dietary levels. Fish fed with 1% BW day−1 had higher hepatic Na+/K + -ATPase (NKA) and glucose-6-phosphate dehydrogenase (G6PDH) activities than others, whereas fish fed with 3% BW day−1 had the highest muscle phospho-pyruvate kinase (PK) and G6PDH (P < 0.05). Fish reared with 5% BW day−1 had the highest total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity and the lowest malondialdehyde (MDA) contents in the liver. Fish fed with 3% BW day−1 had the highest antioxidant indices [T-AOC, SOD and glutathione peroxidase (GSH-PX)] and the lowest MDA contents in the muscles (P < 0.05). Based on WG, SGR, FCR, digestive enzyme activities, and nutrient absorption and utilisation, the recommended feeding level for juvenile Yangtze sturgeon (average initial weight of 67.80 ± 0.19 g) is 3% BW day−1 when they are kept at 20.3 ± 1.3 °C. These data reveal that fish would tend to balance metabolism and growth by optimising nutrient absorption and utilisation when fed at different dietary levels.