Yellowfin, as its name implies, is distinguished from other tunas by a long, bright-yellow dorsal fin and a yellow strip down its side. It’s also more slender than bluefin. With its flashy markings, the yellowfin tuna is especially impressive at night. Fishermen say that when watching yellowfin feed, it’s easy to see why they carry the Hawaiian name ahi, or fire. Yellowfin is the most tropical species of tuna, abundant in warm waters throughout the Pacific and Atlantic, often mixed with other species, especially skipjack tuna. The fish is most often harvested by purse seine, but the best-quality yellowfin is caught by hook and line. Market size runs from 7 1/2 to 20 pounds. High-quality fresh yellowfin comes from Hawaii, Florida, Mexico, southern California and the Gulf of California. Tuna is often canned in countries other than those harvesting it. Top canning countries exporting tuna to the United States include Thailand, the Philippines and Indonesia.