Effects of dietary protein levels on growth, body composition and health status of paddlefish (Polyodon spathula)

An 8-week growth trial was conducted to determine the effects of dietary protein levels on growth, body composition and health status of paddlefish (Polyodon spathula). Five experimental diets were formulated to contain 35.44%, 37.20%, 39.19%, 42.05% and 45.30% dietary crude protein (CP) with 5% lipid levels, respectively. At the end of the experiment, fish fed 35.44% to 42.05% CP diet resulted in significantly higher weight gain rate and specific growth rate, and both decreased at 45.30% CP level. The protein efficiency rate did not change significantly when the dietary CP increased from 35.44% to 42.05%; however, it significantly decreased when protein level reached 45.30%. The body composition of the experimental fish did not change significantly with the increase of dietary protein levels. The protein apparent digestibility coefficients (ADC) of 39.19% CP level is significant higher compared with other groups, which was contrary to lipid ADC and dry matter ADC. Liver lipase activity of P. Spathula peaked with the fish fed 42.05% CP level. The highest superoxide dismutase activity of the P. spathula was observed in the 37.20% treatment, and the activity of catalase significantly increased when CP level reached 39.19% compared to the 35.44% treatment. Based on second-order polynomial regression analysis of weight gain rate and specific growth rate, the recommended dietary protein level for P. spathula diet is 40%-41%.