Side by Side

Bluefin Tuna Thunnus thynnus

Typical: 40–73 in, 50–300 lb

Quickest tell: The distinctly SHORT pectoral fin (not reaching the second dorsal), the dull dusky finlets, and the heavy football body separate bluefin from the long-pectoraled bigeye and the long-finned, yellow-striped yellowfin; bluefin alone has a heavily striated liver, the definitive lab check.

• very short pectoral fins (clearly not reaching back to the second dorsal)
• short second dorsal and anal fins
• dark metallic blue-black back, silver-white belly with no bright yellow stripe
• dusky/grayish finlets edged with a thin black line (not bright yellow)
• stout, deep, football-shaped body

Full Bluefin Tuna guide — season, gear and rules →

Yellowfin Tuna Thunnus albacares

Typical: 36–50 in, 30–80 lb

Key field mark: Long, bright-yellow sickle-shaped dorsal and anal fins plus yellow black-edged finlets distinguish yellowfin from the much smaller blackfin, which keeps short fins and dark, dusky finlets.

• Dark metallic blue back, silvery-white belly, and a golden-yellow stripe down the side
• Greatly elongated, sickle-shaped (falcate) second dorsal and anal fins on larger adults
• Bright yellow finlets edged with a narrow black margin
• Lower flanks/belly often marked with alternating pale lines and rows of dots
• Pectoral fin moderately long, reaching to about the second dorsal origin (not past the anal fin as in bigeye)

Full Yellowfin Tuna guide — season, gear and rules →

When Each Is Running July — current month highlighted

Where Bluefin Tuna and Yellowfin Tuna Overlap

Both run in Mid-Atlantic, Northeast, Southern California — that is where telling them apart actually matters.

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