Aquaculture is a vital component of global food security, and optimizing growth efficiency is a persistent industry goal. Environmental manipulation, particularly through light spectrum control, has emerged as a promising non-invasive strategy. Among various wavelengths, blue light has consistently demonstrated a growth-promoting effect, termed the "blue light effect," across diverse fish species. While the phenotypic outcome is documented, the fundamental biological mechanism-how a light signal is perceived, transduced into a systemic physiological response, and ultimately manifested as accelerated somatic growth-remains fragmented and inadequately understood. Critical knowledge gaps persist regarding the specific endocrine pathways activated, the molecular-level changes in key metabolic tissues (especially the central nervous system and skeletal muscle), and how these changes are coordinated across organs to produce the net growth phenotype. This study aimed to move beyond correlative observation and mechanistically decipher this process. Using the economically important largemouth bass (Micropterus salmoides) as a model, our primary objectives were to: 1) confirm the growth-enhancing effect of blue light under controlled, multi-spectral conditions; 2) identify the core endocrine axis mediating this effect; 3) elucidate the tissue-specific transcriptional and metabolic reprogramming in the brain (the signal processing center) and skeletal muscle (the primary growth effector organ); and 4) integrate these multi-level findings to propose a coherent, cross-tissue molecular regulatory network. To achieve these objectives, we conducted a comprehensive, multi-phase investigation. A 90-day controlled cultivation trial was performed, where juvenile largemouth bass were randomly allocated into five groups exposed to distinct light spectra: White (W, control), Blue (B), Green (G), Orange (O), and Red (R), under a standardized 12h:12h light-dark photoperiod. Water quality parameters (temperature: 20-25 °C; dissolved oxygen >6 mg/L) were meticulously maintained. Growth metrics (body weight, length) were longitudinally recorded. At the trial terminus (90 days post-initiation), fish from the W and B groups, stratified by sex (White Female/WF, White Male/WM, Blue Female/BF, Blue Male/BM), were selected for in-depth analysis. Detailed morphometric measurements were taken, and tissues were collected. Systemic endocrine response was assessed by quantifying serum levels of Growth Hormone (GH) and Insulin-like Growth Factor 1 (IGF1) using enzyme immunoassay (EIA). To uncover the molecular underpinnings, total RNA was extracted from brain and white muscle tissues of biological replicates. RNA-seq was performed on the Illumina platform (PE150). Subsequent bioinformatic analyses encompassed differential gene expression analysis, Principal Component Analysis (PCA) for assessing global transcriptional patterns, KEGG pathway enrichment analysis to identify activated or suppressed biological processes, and construction of Protein-Protein Interaction (PPI) networks to visualize potential regulatory hubs. Key transcriptomic findings related to growth and protein metabolism were validated using quantitative real-time PCR (qRT-PCR). Our integrated approach yielded a coherent chain of evidence. 1) Phenotypic confirmation: The growth trial confirmed a significant blue light-specific advantage. While initial growth (0-45 days) was similar across W, B, G, and O groups, the B group exhibited a significant weight gain advantage from day 60 onward, achieving the highest final average weight. Notably, this growth was accompanied by a selective increase in the hepatosomatic index (HSI), suggesting a specific role for liver metabolism. 2) Endocrine activation: EIA analysis revealed a clear endocrine trigger. Serum concentrations of both GH and its downstream effector, IGF1, were significantly elevated in BF and BM fish compared to their WF and WM counterparts, establishing the activation of the somatotropic (GH/IGF1) axis. 3) Molecular reprogramming in muscle: Transcriptomic analysis of muscle tissue provided a mechanistic link. We observed a significant downregulation of the potent negative growth regulator myostatin (mstnb) in males. Concomitantly, a suite of genes central to the ubiquitin-proteasome system (UPS)-the primary pathway for targeted protein degradation-was consistently suppressed. This included ubiquitin-conjugating enzymes (ube2, ube4) and multiple proteasome subunit genes (psma, psmb, psmc, psme), indicating a profound inhibition of muscle protein catabolism. 4) Brain-specific signaling: In the brain, PCA confirmed light condition as the major driver of transcriptional variation. KEGG enrichment analysis of DEGs highlighted significant involvement in Neuroactive ligand-receptor interaction and the MAPK signaling pathway, implicating blue light in modulating neuroendocrine communication and cellular proliferation/stress responses. 5) Muscle metabolic shifting: In muscle, pathway analysis pointed toward a metabolic adaptation, with enrichment in PPAR signaling pathway, Cardiac muscle contraction, and Adrenergic signaling in cardiomyocytes, suggesting enhanced energy mobilization and utilization to support growth. 6) Integrated network model: Synthesizing these findings, we constructed tissue-specific PPI networks using cross-sex conserved DEGs. By overlaying the enriched pathway information, we proposed a novel, multi-organ "brain-liver-muscle" axis regulatory network. This model posits that blue light perception in the brain stimulates the GH/IGF1 axis, leading to elevated systemic IGF1. IGF1 then orchestrates a dual anabolic program in muscle: promoting synthesis while concurrently suppressing degradation via UPS inhibition. The liver, evidenced by its increased size, acts as a central metabolic and endocrine (IGF1 production) hub supporting this process. This study reveals that blue light promotes largemouth bass growth via multi-organ physiological and molecular reprogramming, not merely through behavioral or stress responses. We propose an integrative model linking central neuroendocrine activation to enhanced peripheral anabolism and suppressed catabolism. The work provides the first mechanistic dissection connecting blue light to GH/IGF1 axis activation and specific inhibition of the UPS in muscle. By constructing a cross-tissue regulatory network, it establishes a novel systems-level framework for understanding environmental regulation of growth. These findings advance fish environmental physiology and support the development of precision light-regime technologies for sustainable aquaculture. Future studies should explore interactions with diet and temperature, and applicability across life stages and species.