Optimizing Muscle Quality in Common Carp (Cyprinus carpio L.): Impacts of Body Size on Nutrient Composition, Texture, and Volatile Profile

To investigate the effect of body size on muscle quality of common carp (Cyprinus carpio L.), we systematically tracked the dynamic changes in nutrient content, texture, and volatile organic compounds (VOCs) among small-sized (~100 g), medium-sized (~250 g), and large-sized (~600 g) fish (SYRC, MYRC, and HYRC, respectively) over a 30-week feeding trial. The results indicated that the HYRC showed significantly reduced moisture and lipid content, along with increased protein content, hydroxyproline, hardness, and chewiness compared to the SYRC (p < 0.05). The long-chain polyunsaturated fatty acids (LC-PUFAs) and fish lipid quality in the MYRC were significantly lower than those in both the SYRC and HYRC (p < 0.05). The HYRC demonstrated an elevated health-promoting index and a reduced atherogenicity value compared to the SYRC (p < 0.05). The contents of alcohol, ketones, and furans in the HYRC increased by 32.53%, 44.62%, and 144.29%, respectively, compared with those in the SYRC (p < 0.05), including key VOCs in aquatic products such as oct-1-en-3-ol and pent-1-en-3-ol. In conclusion, the SYRC have higher levels of LC-PUFAs and lower hardness; the MYRC have poor levels of LC-PUFAs; and the HYRC have an optimal synergy of nutrition, texture, and VOCs, but the overaccumulation of undesirable VOCs requires mitigation. This provides theoretical references and data support for fish quality optimization, processing, and consumption guidelines.