Within-cohort growth heterogeneity constrains aquaculture productivity, and its molecular correlates in carnivorous teleosts are poorly described. We compared the three heaviest and the three lightest individuals (n = 3 biological replicates per group, one fish per replicate) from a single cohort of mandarin fish (Siniperca chuatsi) at 90 days post-hatch, which differed 3.09-fold in body mass (p = 7.1 × 10⁻⁵), by combining muscle RNA sequencing with label-free quantitative proteomics of muscle and liver. Muscle transcriptomics identified 827 differentially expressed genes. The proteasome (ko03050) was the only KEGG pathway reaching significance, with all 14 contributing subunits being more abundant in slow-growing fish, and GO enrichment recovered proteasome, peptidase and endopeptidase complexes alongside serine-type peptidase activities in the same direction. Proteomics identified 37 differentially abundant proteins in muscle and 24 in liver at a nominal threshold. Protein-level gene set enrichment analysis showed negative enrichment of oxidative phosphorylation (NES = −1.96, adjusted p = 0.001) and of mitochondrial proteins (NES = −1.77, adjusted p = 0.005) in fast-growing muscle. Haemoglobin subunits were more abundant in fast-growing muscle and liver at the protein level, while muscle haemoglobin transcripts showed paralog-specific differences. The cross-sectional extreme-phenotype design identifies molecular signatures associated with the observed growth phenotype without establishing causality. The dataset provides candidate genes and proteins for functional study in S. chuatsi.