Tuna are large, fast-swimming, migratory predatory fish found in oceans worldwide. They play a significant role in marine ecosystems as both predators and prey, and are a globally important food source, supporting major commercial fisheries.
Understanding Tuna Diversity
The term “tuna” is widely used. It refers to true tunas (genus Thunnus, eight distinct species) and other closely related tuna-like species within the broader Scombridae family.
The True Tuna Species
Within the Thunnus genus, there are eight recognized species.
Albacore Tuna (Thunnus alalunga)
Albacore tuna are distinguished by their exceptionally long pectoral fins, which can extend beyond the start of the second dorsal fin. They typically have a dark metallic blue back and silvery-white sides. They grow up to 4.5 feet (1.4 meters) long and weigh around 100 pounds (45 kilograms). Found in temperate and tropical waters of the Atlantic, Pacific, and Indian Oceans, their white, delicate flesh is highly valued.
Atlantic Bluefin Tuna (Thunnus thynnus)
Atlantic bluefin tuna are robust, muscular fish with a dark blue back and a silvery-white underside. They can reach lengths of 10 feet (3 meters) and weigh over 1,300 pounds (590 kilograms). These highly migratory fish inhabit the Atlantic Ocean and the Mediterranean Sea, prized for their rich, red, marbled flesh, especially in high-end sushi markets.
Yellowfin Tuna (Thunnus albacares)
Yellowfin tuna are easily identifiable by their dark blue back and distinctive bright yellow second dorsal fin, anal fin, and finlets. They grow up to 8 feet (2.4 meters) long and exceed 400 pounds (180 kilograms). These fish are prevalent in tropical and subtropical waters of the Atlantic, Indian, and Pacific Oceans, popular for sushi and grilled dishes.
Bigeye Tuna (Thunnus obesus)
Bigeye tuna resemble yellowfin but have noticeably larger eyes. Their bodies are dark metallic blue on the back, fading to silvery-white on the sides and belly. They can reach about 7.5 feet (2.3 meters) and weigh up to 460 pounds (209 kilograms). Found in subtropical and tropical regions of the Atlantic, Indian, and Pacific Oceans.
Blackfin Tuna (Thunnus atlanticus)
Blackfin tuna are the smallest species within the Thunnus genus, typically reaching 3 feet (1 meter) and 30 pounds (14 kilograms). They have a dark metallic-blue back, yellow sides, and a silver underbelly. Their distribution is limited to the western Atlantic Ocean, ranging from Cape Cod to Brazil.
Longtail Tuna (Thunnus tonggol)
Longtail tuna are characterized by their elongated bodies and relatively long caudal fins. They generally have a dark blue to black back and silver sides, growing up to 4.7 feet (1.45 meters) in length. Primarily found in the Indo-West Pacific, inhabiting coastal and offshore waters.
Southern Bluefin Tuna (Thunnus maccoyii)
Southern bluefin tuna possess a robust, muscular body with dark blue coloration. They can reach lengths of 8 feet (2.4 meters) and weigh over 440 pounds (200 kilograms). These highly migratory fish are found in the Atlantic, Indian, and Pacific Oceans, particularly in temperate waters of the Southern Hemisphere.
Pacific Bluefin Tuna (Thunnus orientalis)
Pacific bluefin tuna are large, predatory fish with a dark blue or black dorsal side and a silvery-white belly, often with grayish-green iridescence. They grow up to 9.8 feet (3 meters) and weigh as much as 990 pounds (450 kilograms). Primarily found in the northern Pacific Ocean, they are highly migratory.
Other Prominent Tuna-Like Species
Beyond the Thunnus genus, several other species are commonly recognized and fished as tuna due to their similar appearance and ecological roles. These species often share habitats with true tunas and contribute significantly to global fisheries.
Skipjack Tuna (Katsuwonus pelamis)
Skipjack tuna are among the most abundant and commercially important tuna species. They have streamlined bodies with dark purplish-blue backs and silvery bellies marked by four to six distinct dark bands. They reach up to 3 feet (1.1 meters) and 40 pounds (18 kilograms). Found in tropical and warm-temperate waters worldwide, often swimming in large schools near the surface.
Bonito (Sarda species)
Bonito are a group of medium-sized, predatory fish within the mackerel family, often mistaken for tuna due to their torpedo-shaped bodies. They have striped backs and silvery bellies, growing to 30 inches (75 cm) and 25 pounds. Bonito species are found in temperate and tropical oceans globally.
Dogtooth Tuna (Gymnosarda unicolor)
Despite its common name, dogtooth tuna is not a true tuna but belongs to the bonito group. It is named for its large, conical teeth and has a streamlined body with a blue-green back, silvery sides, and a whitish belly. Dogtooth tuna can reach 8.2 feet (2.5 meters) and weigh over 280 pounds (127 kilograms). Found in the Indo-Pacific, typically around coral reefs and seamounts.
Little Tunny (Euthynnus alletteratus)
Little tunny are smaller, robust-bodied fish with a dark, wavy pattern on their backs and several dark spots between their pectoral and pelvic fins. They typically grow to 3 feet (1 meter). These fish are common in the Atlantic Ocean, including the Mediterranean Sea, and are often found in coastal and offshore waters.
Bullet Tuna (Auxis rochei)
Bullet tuna are small, fast-swimming fish with a robust, rounded body that tapers quickly towards the tail. They have a dark blue or black back and silvery sides, with indistinct wavy lines on their upper back. Distributed in tropical and temperate waters of the Atlantic, Indian, and Pacific Oceans, often forming large schools.
Frigate Tuna (Auxis thazard)
Frigate tuna are similar to bullet tuna but generally slightly larger, with a more compressed body. They also exhibit dark wavy markings on their upper back and silvery sides. These pelagic fish are found in warm waters worldwide, often schooling near the surface and feeding on small fish and crustaceans.
Mackerel Tuna (Euthynnus affinis)
Mackerel tuna, also known as kawakawa, have a distinct pattern of broken diagonal lines on their upper sides and several dark spots above the pelvic fin. They grow up to 3.3 feet (1 meter). These species are found throughout the tropical and temperate Indo-West and Central Pacific Oceans, inhabiting coastal and offshore waters.
Conservation and Sustainability
Many tuna populations face significant challenges due to overfishing. Bluefin tuna species (Atlantic, Pacific, Southern) and Bigeye tuna have experienced declines, largely driven by demand. Efforts to manage tuna fisheries more sustainably are underway, with some species showing signs of recovery. Consumers can contribute by choosing sustainable tuna products (e.g., MSC label) and selective fishing methods like pole-and-line or troll-caught, which minimize bycatch.