Abstract: To investigate the effects of dietary replacement fishmeal protein with Hermetia illucens larvae meal (HM) on growth performance, digestive capacity, plasma biochemical indexes and related genes expression in Hefang crucian carp (Carassis auratus), five isonitrogenous (30%), isolipidic (6%) and isoenergetic (18.50 MJ/kg) diets were formulated to contain graded levels of fishmeal protein replacement by HM (0, 20%, 40%, 60% and 80% respectively) for a 74-day feeding trial. Each treatment was randomly assigned to triplicate groups of 25 fish initial body weight of (31.50±0.50) g per aquarium. Fish were fed twice daily to apparent satiation. Results showed that the weight gain rate (WGR) and specific growth rate (SGR) first increased and then decreased with the increased proportion of HM in diets, with a maximum in the 20% substitution group. Feed conversion ratio (FCR) showed an initial decrease followed by an increase, and the 20% substitution group was significantly less than 60% and 80% substitution groups (P<0.05). With the increased proportion of HM in diets, condition factor (CF) and viscerosomatic index (VSI) first increased and then decreased, with a maximum in the 40% substitution group. The hepatopancreas somatic index (HSI) of 80% substitution group was significantly higher than those in 0, 20% and 60% substitution groups (P<0.05), but there was no significant difference between 40% and 80% substitution group. The moisture and ash of fish body expressed no significant difference. However, crude protein of body in 20% and 60% substitution group was significantly lower than that in 0 group (P<0.05). Crude lipid of body showed an initial increase followed by a decrease, and the highest value was seen in 20% substitution group. There was no significant difference in plasma glucose concentration, total cholesterol concentration, alanine aminotransferase and aspartate aminotransferase activity, but blood ammonia content showed an upward trend, the blood ammonia of 80% substitution group was significantly higher than that of 0 substitution group. Total plasma amino acid in the 20% substitution group was significantly higher than those in the other treatments (P<0.05). Plasma malondialdehyde was significantly lower in 60% and 80% substitution groups than that in 20% substitution group (P<0.05). The expression of lat2, pept1 and cdx2 genes in the intestine reached to the highest level in 20% substitution group, while asct2 gene showed the highest expression in 40% substitution group. The expression of tor and igf1 genes in liver was the highest in 40% substitution group, while the highest expression of gh and ghr genes were seen in 60% substitution group. These results suggested that 0—40% of fish meal in the diet of HCC could be substituted by HM, and 20% was the optimal optimum proportion.