Side by Side

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 →

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 →

When Each Is Running July — current month highlighted

Where Bigeye Tuna and Bluefin Tuna Overlap

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

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