Yellowfin Tuna

A Hot-Rodded Torpedo

The yellowfin tuna runs its engine warm. Its swimming muscle is regionally endothermic: warmed in part by heat the fish makes itself. Researchers testing slow muscle fibres from yellowfin and from bonito (a cooler-running relative) found that a counter-current heat exchanger, a plumbing trick where outgoing and incoming blood trade heat, holding a 10 degrees C difference would typically double the muscle’s maximum power output.

Yellowfin are torpedo-shaped, metallic dark blue on the back, and yellow to silver on the belly, with bright-yellow dorsal and anal fins and finlets. A study of tunas found a hydraulic system in their median fins (the fins along the midline of the body): fin muscles, bones and lymphatic vessels (part of the system that manages body fluid) are involved in controlling them.

Cold plunge Tagged yellowfin in the South Atlantic dived to a maximum depth of 1,014 m and met water as cold as 6.4°C.

Grow Fast, Spawn Often

NOAA Fisheries says yellowfin grow fast, up to 6 feet long and 400 pounds. The same agency gives the Pacific stock a somewhat short life span of 6 to 7 years, though FishBase lists a maximum reported age of 18 years.

NOAA calls them very productive. Most can reproduce by age 2, and females can spawn almost daily, releasing millions of eggs each time.

Cruising the Whole Ocean

Yellowfin live in tropical and subtropical oceans around the world, and FishBase lists them as absent from the Mediterranean. They are highly migratory. Some adults tagged off Kaua’i in Hawaii made rapid dispersals of more than 800 km, and NOAA says yellowfin can swim across an entire ocean.

Their days and nights differ. Tags in the South Atlantic showed fish staying shallow, under 50 m, through the night, then spending more of the day deep, past 100 m. They feed near the top of the food chain on fish, squid and crustaceans, and they are known to gather around floating debris, anchored buoys and dolphins. Marine mammals, billfish and sharks feed on the adults.

Holding Up

The latest Red List assessment rates the species Least Concern. NOAA’s most recent assessments (2023 for the Eastern Pacific stock, 2020 for the Central and Western Pacific) find both stocks neither overfished nor subject to overfishing. In 2024, US commercial landings of Pacific yellowfin totalled 9.8 million pounds.