Pacific bluefin tuna

The bluefin tuna is a big fish.

It lives in the big ocean. This fish can stay warm in cold water. This helps it swim fast.

It eats small fish and squid. The fish can live for many years. People catch them to make food. Some people even farm them in the sea. This fish is very special to see.

The Pacific bluefin tuna is a large fish.

It lives in the North Pacific Ocean. These fish swim from Asia to North America. They can also visit the South Pacific.

Most fish are cold-blooded. This means their body temperature matches the water. But tuna are warm-blooded. They can control their own heat. They use special parts near their muscles called retia mirabilia. These parts are a set of tiny veins and arteries. They work like a heat exchanger. This keeps heat inside the fish. Being warm gives them extra power and speed.

These fish eat squid and small fish. They also eat crabs and krill. A single female can lay up to 25 million eggs.

People catch many tuna for food. In Japan, chefs use the fatty belly meat for sushi. This meat is called toro. For many years, too many tuna were caught. This is called overfishing. People worked to fix this. In 2024, experts found the population had rebuilt. It is now a success story.

The Pacific bluefin tuna is a huge and powerful fish.

It lives mostly in the North Pacific Ocean. This fish swims between the coast of East Asia and North America. It is a migratory species, so it travels long distances. Sometimes, it even visits the South Pacific near places like Australia and New Zealand. These fish are very important to people around the world.

Most fish are cold-blooded, meaning their body temperature matches the water. However, the Pacific bluefin tuna is warm-blooded. It can regulate its own heat using special organs near its muscles. These organs are called retia mirabilia. This is a system of tiny veins and arteries that work together. They act like a heat exchanger to keep warmth inside the body. This extra heat gives the tuna more power and speed. It also lets the fish swim in many different water temperatures.

Scientists and fishers have studied these tuna for a long time. In 1979, Kinki University in Japan first successfully farmed young tuna. Later, they even succeeded in breeding them in a lab. These farm-raised fish are now called Kindai tuna. The tuna is also a famous prize for people who fish for sport. In 2014, a person named Donna Pascoe caught a huge record-breaking fish. This happened on a boat named Gladiator during a national tournament.

These fish grow to be very large and heavy. A mature tuna is about 1.5 meters long and weighs 40 kilograms. Some even reach much larger sizes. One report mentioned a mass of up to 450 kilograms. They eat many things like small squid, fish, and even red crabs. When they are ready to have babies, they spawn in the Philippine Sea or the Sea of Japan. A single large female can carry as many as 25 million eggs.

People catch many tuna for food, especially in Japan. Chefs love the fatty belly meat, which they call toro. This meat is used for very special sushi and sashimi. Sometimes, a single tuna can sell for millions of yen at a fish market. In 2019, a fish caught near Oma sold for 333.6 million yen. For a long time, too many tuna were being caught. This was called overfishing, and it was a big problem. However, people worked to fix this by catching fewer fish. By 2024, experts found the population had rebuilt successfully.

The Pacific bluefin tuna, known scientifically as *Thunnus orientalis*, is a powerful predatory fish.

It lives primarily in the northern Pacific Ocean. This species ranges from the coasts of East Asia to the western coast of North America. While it is mainly a pelagic species, meaning it lives in the open ocean, it can also be found in tropical and coastal regions. It typically swims from the surface down to depths of 200 meters, but it has been seen as deep as 1,000 meters. Because it is migratory, it travels vast distances across the sea.

Most fish are ectothermic, which means they are cold-blooded. Their body temperature changes based on the water around them. The Pacific bluefin tuna is different because it is warm-blooded. It can regulate its own internal temperature through a process called thermoregulation. This happens using special organs near the muscles called retia mirabilia. These organs consist of many tiny, parallel veins and arteries. As warm blood in the veins returns to the gills, it touches cold, newly oxygenated blood in the arteries. This system acts as a counter-current heat exchanger. It transfers heat from the veins to the arteries so warmth is not lost through the gills. This allows the tuna to maintain extra power and speed in its muscles. It also means the fish is not limited by water temperature or climatic changes.

The life cycle of the Pacific bluefin tuna involves several distinct stages. They generally reach maturity at about five years of age. The generation length, or the average time between generations, is estimated at 7 to 9 years. Depending on the source, their total longevity can be 15 or even 26 years. When they reach maturity, they are usually about 1.5 meters long and weigh 40 kilograms. However, they can grow much larger. Some individuals have been reported to reach a mass of up to 450 kilograms. During the spawning season, which occurs from April to August, females produce many eggs. A large female can carry between 5 million and 25 million eggs. Spawning locations vary by region, occurring in the northwestern Philippine Sea or the Sea of Japan.

Humans have a long history of interacting with this species through fishing and science. In 1979, Kinki University in Japan successfully farmed already-hatched bluefin tuna. By 2002, they succeeded in breeding them, and they repeated this for a third generation in 2007. These farm-raised fish are now known as Kindai tuna. For sport fishers, the tuna is a legendary prize. On February 19, 2014, Donna Pascoe set an all-tackle game fish record. She caught the fish while on the charter boat *Gladiator* during a national tournament.

Historically, the Pacific bluefin tuna faced serious challenges from overfishing. For decades, the species was considered overfished due to heavy commercial catches. In 2011, catches were reduced to help rebuild the population. This effort proved successful according to a 2024 stock assessment. The population grew from a low of about 2 percent of historic levels in 2010 to about 23 percent in 2020. Because of these management measures, the species is now considered a management success. While the IUCN still lists them as "Near Threatened," the 2024 assessment shows they are no longer overfished.

The tuna is also highly significant in global cuisine, especially in Japan. About 80 percent of Pacific and Atlantic bluefin tunas are consumed in Japan. Sushi chefs prize the fatty belly meat, which is called toro. Some tuna are so valuable they fetch incredible prices at auctions. On January 5, 2013, a tuna caught near northeastern Japan sold for 155.4 million yen at the Tsukiji fish market. In 2019, a fish caught off Oma sold for 333.6 million yen at the Toyosu fish market.

Understanding the Pacific bluefin tuna connects us to many larger scientific and global systems. Their migratory patterns require management by several different Regional Fisheries Management Organisations. Sometimes these groups give conflicting advice, which can make conservation difficult. Scientists also study the tuna to understand mercury and PCB levels in fish flesh. These substances can be harmful to humans who eat them. Managing the tuna involves balancing the needs of the commercial fishery with the health of the ocean ecosystem.