Metabolic Mechanisms of Coloration and Decoloration in Juvenile Blood Parrotfish (Vieja melanurus ♀ × Amphilophus citrinellus ♂) Revealed by UHPLC-Q-TOF/MS

Abstract This study explored the role of astaxanthin, a carotenoid supplement, in the metabolic mechanism underlying body color formation in juvenile blood parrotfish (Vieja melanurus ♀ × Amphilophus citrinellus ♂) cultured in a recirculating aquaculture system. Fish were divided into three groups: a control group (C) fed a basal diet for 12 weeks, a coloration group (AX) fed an astaxanthin-enriched diet for 12 weeks, and a decoloration group (AXM) fed the enriched diet for 6 weeks followed by a basal diet for another 6 weeks. Using UHPL-Q-TOF/MS, key metabolic pathways and compounds associated with coloration and decoloration were characterized. Metabolic analysis identified 2007 differentially expressed metabolites (DEMs), with OPLS-DA clearly distinguishing skin metabolite profiles between the AX and AXM groups. Notably, compounds such as astaxanthin, all-trans-4-ketoretinoic acid, octadecanoic acid, myristic acid, 1-oleoyl-2-myristoyl-sn-glycero-3- phosphocholine, (+)-.alpha.-tocopherol, and linoleic acid were significantly elevated in the AX group while prostaglandin i2, pc 38:7, N-tetracose-noyl-4-shingenine, lauroyl-1-carnitine, and (z)-5,8,11-trihydroxyoctadec-9-enoic acid were reduced in AXM group. KEGG pathway analysis revealed enrichment of ABC transporters, biosynthesis of amino acids, protein digestion and absorption, aminoacyl-tRNA biosynthesis, glycine, serine, and threonine metabolism in the AX group. In contrast, galactose metabolism, D-arginine and D-ornithine metabolism, taurine and hypotaurine metabolism were significantly enriched in AXM group. These findings enhance our understanding of the metabolic basis of body coloration in blood parrotfish and offer insights for optimizing ornamental fish nutrition and feed strategies.