Coordinated Bone-Muscle Axis Association in South China Carp (Cyprinus carpio rubrofuscus) with Low Bone Mineral...

South China carp (Cyprinus carpio rubrofuscus) with low bone mineral density (BMD), characterized by softened bones and wavy ribs, were identified during paddy field aquaculture. This study investigated the association between bone status and muscle traits by comparing muscle texture, nutritional composition, histology, ultrastructure, and proteomic profiles between low-BMD fish (BMD-low, ≤0.02 g/cm²) and normal-BMD fish (BMD-normal, ≥0.04 g/cm²). Compared with the BMD-normal group, the BMD-low group showed significantly lower muscle resilience and chewiness, significantly higher iron content, and significantly lower methionine and histidine contents (p < 0.05). Histological analysis revealed increased muscle fiber density, reduced muscle fiber cross-sectional area, and greater intramuscular lipid accumulation in the BMD-low group (p < 0.05). Ultrastructural observations further showed myofibrillar disorganization and elongated sarcomeres and A-bands (p < 0.05). Proteomic analysis identified 21 differentially expressed proteins, including up-regulated desmin a and down-regulated nebulin. KEGG enrichment indicated that these proteins were mainly involved in the cytoskeleton in muscle cells, calcium signaling, regulation of actin cytoskeleton, and ubiquitin-mediated proteolysis. These findings provide new insights into the relationship between bone status and muscle quality in South China carp and support future quality evaluation and selective breeding.