Antarctic krill (Euphausia superba), which is rich in astaxanthin, has been widely utilized as a dietary supplement in fish aquaculture. Our study was to feed juvenile leopard coral grouper (Plectropomus leopardus) a diet containing 50 % Antarctic krill, revealing significant body color differentiation between a reddened group (BKR) and a non-reddened group (BKB), followed by comparative analysis with the control group (BCon) without krill supplementation. Histological analysis and carotenoid content in the liver and intestine were differentially regulated in color-differentiated individuals. Transcriptomic profiling revealed differentially expressed genes (DEGs) among color-differentiated individuals, with up-regulated DEGs in BKR being linked to carotenoid uptake, metabolism, and transport. Key DEGs (acss2l, insig1, fabp7, and bco1) were validated through qRT-PCR and FISH. Additionally, WGCNA identified potential gene regulatory networks in the liver and intestine that were responsive to the body coloration. This study elucidates the molecular mechanisms by which Antarctic krill influences carotenoid-based body coloration, offering new insights into the application of Antarctic krill in aquaculture.