What key feature distinguishes yellowfin tuna from the blackfin tuna species?

The striking, bright yellow second dorsal and anal fins/finlets

The most definitive visual characteristic setting the yellowfin tuna apart from similar species, such as the blackfin tuna, lies in the brilliant coloration of its posterior fins. Specifically, the second dorsal fin, the anal fin, and the series of finlets leading toward the tail exhibit a vivid, bright yellow hue. While yellowfin tuna share features like large eyes, a torpedo shape, and dark coloration dorsally, it is this unique yellow pigmentation that directly contributes to its common name and serves as a reliable field identifier. This feature is crucial because distinguishing between closely related tuna species is necessary for accurate stock assessment and targeted commercial harvesting.