Tuna

Lore & Background

Tunas are sleek, elongated, and streamlined fish adapted for speed, with two closely spaced dorsal fins, the first depressible into a groove. Their body is countershaded—metallic dark blue above and silvery below—and they have a thin caudal peduncle with three stabilizing keels on each side. Unlike most fish, tuna muscle tissue ranges from pink to dark red due to high myoglobin levels, enabling oxygen-rich blood delivery to muscles.

Tunas achieve endothermy through a rete mirabile, a counter-current heat exchange system that conserves metabolic heat, allowing them to elevate the temperature of skeletal muscles, eyes, and brain. This supports faster swimming and survival in cooler waters. However, cavitation—the formation of vapor bubbles around fins—limits their maximum swimming speed, as the bubbles create a vapor film that slows them.

The term 'tuna' likely comes from Spanish atún, via Andalusian Arabic and Middle Latin thunnus, and ultimately from Ancient Greek θύννος (thýnnos). While often interpreted as meaning 'to rush, dart along', the etymology is not definitively settled and may involve a pre-Greek substrate. An alternative term is 'tunny', and in English it has been called 'Chicken of the Sea', a name that persists in Japan as シーチキン (shī chikin).

Reader's Guide

Tuna are among the most commercially important fish globally, with the five principal market species—yellowfin, bigeye, bluefin, albacore, and skipjack—supporting massive fisheries. Annual catches rose from about 300,000 tons in the 1940s to over 4 million tons in recent years, with skipjack comprising about 60% of the catch. Purse-seine nets account for roughly 62% of world production, followed by longline and pole-and-line methods. Overfishing has severely damaged bluefin stocks; for example, Japan was alleged in 2006 to have illegally overfished southern bluefin by taking 12,000 to 20,000 tonnes per year instead of the agreed 6,000 tonnes. Record auction prices for bluefin tuna at Tokyo's Tsukiji and Toyosu markets reflect high demand, with a single fish selling for 333.6 million yen (US$3.1 million) in 2019. The International Seafood Sustainability Foundation (ISSF) has compiled reports on global tuna stocks, and organizations like the WWF warn that without stricter quotas, some stocks face commercial extinction. Tuna's unique physiology—endothermy, high myoglobin, and speed—makes them both a biological marvel and a critical resource requiring careful management.

Did You Know?

• Tuna, opah, and mackerel sharks are not the only fish that can maintain a body temperature higher than the surrounding water; several other fish like billfish and some lamnid sharks also exhibit regional endothermy.
• The Atlantic bluefin tuna can reach a maximum length of 4.6 m (15 ft) and weight of 684 kg (1,508 lb), and is believed to live up to 50 years.
• The term 'tuna' likely comes from Spanish atún, derived from Ancient Greek θύννος (thýnnos), but its etymology is not definitively settled and may involve a pre-Greek substrate.
• Cavitation bubbles create a vapor film around tuna fins that limits their maximum swimming speed.