A New Strain of Preponderant Amphitriploid Clone Juvenile With Integrated Genomes Partly From White Crucian Carp () Requires Low Dietary Protein.

This study was carried out to search for the protein requirement of a new strain of preponderant amphitriploid clone, which integrated genomes partly from white crucian carp (). Seven groups of fish (body weight: 9.73 ± 0.03 g) were fed with seven isolipidic and isocarbohydrate diets containing 21.38%, 25.82%, 27.94%, 31.36%, 34.23%, 37.87%, and 40.70% crude protein (P21, P24, P27, P30, P33, P36, and P39), respectively. After 8-week feeding, weight gain rate (WGR) and specific growth rate (SGR) were lower in the P30 group than those in the P39 group, but no difference was found in final body weight (FBW), survival, condition factor (CF), or hepatosomatic index (HSI) between different groups. Increased dietary protein decreased feeding rate (FR) and viscerosomatic index (VSI) while improved feed efficiency (FE). Decreased protein retention efficiency (PRE) and improved activity of liver alanine aminotransferase (ALT) and content of plasma ammonia suggested intensified fish amino acid catabolism in high dietary protein groups. The dietary protein requirement of the new clone was as low as 21.38% for growth. The optimal dietary protein for high FE was 39.62% and should be less than 30.56% to maintain the maximum protein retention. High dietary protein might be harmful to the fish due to the increased contents of liver malondialdehyde (MDA) and plasma cortisol. Dietary protein level altered fish body and muscle flavor substance composition. Low dietary protein could obtain high muscle fatty acid, free amino acid, and lipid accumulation, including whole body and muscle crude lipid, plasma total triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), and low-density lipoprotein cholesterol (LDL-c). Therefore, the recommended dietary protein for this new clone juvenile should be 21.38%-30.56%.