Abstract: How to improve utilization of protein especially non-fishmeal protein in fish is a problem demanding prompt solution in aquatic nutrition. Studies in mammal showed that G protein coupled receptor family C, group 6, subtype A (GPRC6A) could sense the amino acids, and then regulate the muscle growth via ERK-mTOR signal pathway. But mechanisms of sensing and responding to lysine in fish are still unclear. A 7-week feeding experiment was conducted to investigate the effects of dietary lysine supplementation in low fish meal diets on the growth performances, biochemical composition, nutrient deposition, plasma biochemical indices and metabolism related gene expression in the muscle of gibel carp (Carassius gibelio var. CAS Ⅴ) (initial mean body weight: 8.70±0.03 g). The diet containing 5% fish meal was set as the control group (LL), the other groups were supplemented with 2% (ML) and 4% (HL) lysine, respectively. The results showed that lysine supplementation in low fishmeal diet had no significant effect on the feeding rate (FR), specific growth rate (SGR), feed efficiency (FE), protein retention efficiency (PRE), lipid retention efficiency (LRE) in the gibel carp (P>0.05). Dietary supplement with 2% lysine did not affect the condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) in the gibel carp (P>0.05). The 4% lysine group had no effect on the CF and VSI, but significantly decreased the HSI (P<0.05). The protein content of whole body in ML group was higher than that in other two groups (P<0.05), and the total amino acid level and the total essential amino acid level was also higher than LL group and HL group (P<0.05). The levels of seven essential amino acids including lysine, arginine, isoleucine, leucine, phenylalanine, threonine and valine in the whole body was highest in the fish fed diet supplemented with 2% lysine (P<0.05). The lysine supplementation in low fishmeal diet had no significant effect on the levels of protein and moisture in the muscle of gibel carp (P>0.05), but the HL diet decrease the lipid contents in the muscle (P<0.05). Plasma glucose, triglyceride and cholesterol levels showed no significant difference in the three groups (P>0.05). The diets supplemented with lysine did not affect the plasma amino acid profile in gibel carp (P>0.05). The mRNA levels of genes involved in sensing and responding to lysine including gprc6a, β-arrestins, erk, rheb, tsc2, tor, s6k1, 4ebp2 and eif4e in the muscle of gibel carp were not affected by the diets (P>0.05). The lysine supplementation in low fishmeal diet had no significant effect on relative expression of genes involved in regulating myofiber growth and development including myod, myf5, mstn, mylc and pax7α in the muscle of gibel carp (P>0.05), but the mRNA levels of myog in the HL group was higher than that in the ML group (P<0.05). These results suggested that low fish meal diet supplemented with 2% lysine could increase the total essential amino acid level and protein level in the whole body of gibel carp “CAS Ⅴ”, but the mechanism remains to be fully elucidated, which might offer new insights into improving the feed formula of gibel carp “CAS Ⅴ”.