Density stress is associated with metabolic reprogramming underlying growth-related physiological adaptation in large...

Stocking density is a key environmental stressor that influences growth performance and metabolic regulation in fish; however, the molecular mechanisms underlying density-dependent growth variation in large yellow croaker (Larimichthys crocea) under recirculating aquaculture system (RAS) conditions remain poorly understood. In this study, we investigated the associations between density stress and changes in metabolic regulation and growth-related pathways in L. crocea using an integrated multi-omics approach. Fish were reared for 60 days at low, medium, and high final stocking densities of 7.02, 14.71, and 19.21 kg m^-3, respectively. Integrated transcriptomic and metabolomic analyses of dorsal muscle revealed pronounced density-dependent metabolic remodeling. The greatest transcriptional divergence occurred between the medium- and high-density groups, whereas the most substantial metabolic differences were observed between the low- and high-density groups. Cross-omics analysis identified arginine and proline metabolism, as well as alanine, aspartate, and glutamate metabolism, as key pathways associated with changes in energy supply, anabolic processes, and nitrogen metabolism. High stocking density was associated with a shift toward immediate energy mobilization at the expense of structural maintenance and nitrogen homeostasis, whereas low stocking density showed metabolic instability and compensatory energy dissipation. In contrast, medium stocking density maintained coordinated regulation across these pathways, indicating greater metabolic efficiency. The expression patterns of key genes within these pathways were validated by quantitative real-time PCR. Collectively, these findings suggest that density-dependent differences in growth performance are associated with coordinated metabolic reprogramming in large yellow croaker, and highlight metabolic homeostasis as a key physiological factor associated with density-dependent growth outcomes under controlled RAS conditions.