To investigate the effects of replacing fish meal with fermented Antarctic krill meal on growth performance, body color, and serum biochemical indexes of koi carp, 450 koi carp with an average body weight of (4.92±0.22) g were randomly divided into five groups with three replicates per group and 30 fish per replicate. In the control group, we added unfermented defatted Antarctic krill meal, and in the experimental groups, we added defatted Antarctic krill meal fermented by Enterococcus faecalis, Lactobacillus plantarum, Clostridium butyricum, and compound bacteria (1:1:1), which were termed as ES (control group), EF, LP, CB, and MIX, respectively. The addition amount of Antarctic krill meal in each group was 200 g/kg, and the experiment lasted for 70 days. The results showed the following: Compared with those in the control group, the replacement of fish meal with fermented Antarctic krill meal significantly improved final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) (P<0.05); additionally, the FBW, WGR, and SGR of the MIX group were significantly higher than those in other groups (P<0.05). The carotenoid content in the skin and scales of the experimental group was significantly increased (P<0.05); the red (a*) and yellow (b*) value, and relative expression of tyr in the skin and scales were significantly increased (P<0.05); and the a* and b* values and the relative expression of the tyr gene in the MIX group were significantly higher than those in other groups (P<0.05). The contents of serum triglyceride (TG) and total cholesterol (TC) in the experimental group were significantly increased (P<0.05), whereas the ratio of glutamic oxalate transaminase/alanine transaminase (AST/ALT) and the content of malondialdehyde (MDA) were significantly decreased (P<0.05). The liver cells of the control group showed lipid droplets and vacuolar degeneration. No significant difference was observed in each index among the EF, LP, and CB groups (P>0.05). Based on the above results, using complex bacteria to ferment krill meal in the koi carp feed is recommended with a 20% addition level of defatted krill meal, which can effectively improve the absorption and conversion utilization rate of krill meal.