Abstract: Lean aquaculture is the culture mode of selecting disease-free, injury-free, robust, and marketable adult fish into high-quality water source under a zero-feed regimen. This approach aims to improve the muscle quality of freshwater fish through periods of starvation and exercise. A large number of studies have demonstrated that short-term lean aquaculture can improve the muscle quality of freshwater fish to a certain extent. However, research on the long-term effect of lean aquaculture on the muscle quality of grass carp (Ctenopharyngodon idellus) is limited, necessitating further information for practical applications in aquaculture. In order to investigate the effect of lean aquaculture pattern on the muscle quality of C. idellus, the present study compared the morphometric data, textural characteristics, general nutrients, odorants, amino acid and fatty acid indices of control and lean fish after 8 months of lean aquaculture. The morphometric results showed that the condition factor, viscerosomatic index, hepatosomatic index, and intraperitioneal fat index of lean fish were significantly lower than those of control fish (P<0.05). Additionally, muscle hardness, springiness, gumminess, chewiness, and shearing force were significantly greater in lean fish than that in control fish (P<0.05). Comparison of general nutrients revealed that crude fat and crude protein content in lean fish muscle were significantly lower than those in control fish (P<0.05). The ash content did not significantly differ between the two groups (P>0.05), while the water content was significantly higher in lean fish (P<0.05). Notably, geosmin (GSM) and 2-methylisotretinoin (2-MIB) were undetectable in the muscle of both lean and control fish. Comparison of amino acids showed that the total amino acids (TAA), total essential amino acid (TEAA), and total delicious amino acid (TDAA) in the muscle of lean fish were significantly higher than those in control fish (P<0.05). The percentage of total essential amino acid to total non-essential amino acid (TEAA/TNEAA) and the percentage of total essential amino acid to total amino acid (TEAA/TAA) in lean fish muscle was 87.82% and 42.44%. The percentage of total essential amino acid to total non-essential amino acid (TEAA/TNEAA) and the percentage of total essential amino acid to total amino acid (TEAA/TAA) in the muscle of control fish was 56.91% and 34.98%. The results of amino acid nutritional evaluation showed that the amino acid score (AAS), chemical score (CS), and essential amino acid index (EAAI) were all higher in the muscle of lean fish than those in control fish. Fatty acid analysis showed that the percentages of polyunsaturated fatty acid (PUFA), n-3 PUFA, n-6 PUFA, EPA, and DHA to total fatty acid in lean fish muscle were significantly higher than those in control fish (P<0.05). The study demonstrates that the lean aquaculture pattern can effectively enhance both the body shape and muscle quality of C. idellus. The results of the related research provide foundational information for the exploration of lean aquaculture practices for this species and serve as a reference for the aquaculture production practice.