Abstract The main objective of this experiment was to study the metabolism of arginine in juvenile largemouth bass (Micropterus salmoides). A total of 300 healthy fish (average weight of 25 ± 0.5 g) were randomly assigned to ten groups. Experimental fish were orally administered or intraperitoneally injected with 0.9% sodium chloride, arginine, arginine-aspartate, citrulline, and glutamate solutions, respectively. They were euthanized at 10, 30, 60, 120, and 240 min after oral administration or intraperitoneal injection, and various tissue samples were subsequently collected for analysis. The results revealed that serum ornithine and citrulline concentrations of largemouth bass were significantly increased by oral administration of arginine or arginine-aspartate (P