Comparing the growth, hepatopancreatic and intestinal histology, and growth-related genes expression of “Husu-1” and common Ctenopharyngodon idella at different dietary protein levels

“Husu-1” Ctenopharyngodon idella is the first newly bred C. idella species in China. This study compared the growth performance, digestive enzyme activities, hepatopancreas and intestine histology and growth-related genes expression of common C. idella and “Husu-1” C. idella fed with various dietary protein levels. Four isolipidic diets were designed with crude protein levels of 26% (P26), 29% (P29), 32% (P32) and 35% (P35), and then fed to common C. idella (5.02±0.04) g and “Husu-1” C. idella (6.20±0.05) g for 8 weeks. The weight gain (WG) of C. idella increased significantly with the increasing dietary protein level, and the feed conversion ratio (FCR) decreased significantly. “Husu-1” C. idella showed significantly higher WG, feed intake, condition factor, hepatosmatic index at the same protein level, and lower FCR (except for the 29% protein group) than common C. idella. The crude lipid content and lipid retention of the whole fish increased, while the protein efficiency and protein retention decreased with the increasing dietary protein level. Compared with the common C. idella, “Husu-1” C. idella showed higher protein efficiency, protein retention and lipid retention. The intestinal villus height, muscle layer thickness and trypsin activity gradually increased and α-amylase activity decreased with the increasing protein levels, but no significant differences were observed in the activities of the two digestive enzymes between the 32% and 35% protein groups. The intestinal villus height, muscle layer thickness, α-amylase and trypsin activities, as well as the liver histology were not significantly different between the two C. idella. The expressions of igf-1, tor and s6k1 in the muscle of C. idella fed with high protein diets (32%, 35%) were significantly higher than those of the low protein groups (26%, 29%), but there was no significant difference between the two protein levels of 32% and 35%. Additionally, “Husu-1” C. idella showed significantly higher expressions of igf-1 and s6k1 than common C. idella at dietary protein levels of 32% and 35%. In summary, “Husu-1” C. idella presents better growth performance than common C. idella, which is attributed to the improvement of feed utilization and feed intake.