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Bigeye Tuna Thunnus obesus

Typical: 40–60 in, 60–150 lb

Quickest tell: A large eye plus a long pectoral fin AND short (un-elongated) second dorsal and anal fins separate bigeye from yellowfin; note the liver is SMOOTH (only bluefin has a striated liver), so dockside rely on the big eye and the long pectoral with short median fins.

• noticeably large eye
• very long pectoral fin (reaching past the second dorsal, especially in smaller fish)
• short second dorsal and anal fins (never elongated)
• dark metallic blue back, whitish belly
• bright yellow finlets edged in black

Full Bigeye 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 Bigeye Tuna and Yellowfin Tuna Overlap

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

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