1. The body of yellowfin tuna is spindle-shaped. The sides are slightly flattened, the tail is long and thin, the second dorsal fin and anal fin of the adult are extended, the pelvic fin is in the pectoral position, the caudal fin is crescent-shaped, the caudal peduncle is well developed, and there are 3 ridges on each side. The jaws have small teeth, tapered and arranged in a row. The body is covered with fine scales, and the scales on the chest are larger, forming a breastplate. The lateral line is obvious.

2. The highest point of the body is located in the middle of the base of the first dorsal fin. The first gill arch and gill rake are 26-3 large individuals. The second dorsal and anal fins are very long and curved in an arc, exceeding the fork length by 20. The pectoral fin is longer, extending to or beyond the starting point of the second dorsal fin, but not beyond the end of its base, accounting for 22-31. Vertebrae 18 and 21. The back is blue, the abdomen is silvery white, and the abdomen has 20 disconnected vertical lines. The dorsal fin, anal fin and small fin are all orange.