Pacific bluefin tuna

The Pacific bluefin tuna (Thunnus orientalis) is a predatory fish that lives in the northern Pacific Ocean. Sometimes it travels to the south Pacific too.

In the past, scientists often grouped this fish with another type called the northern bluefin tuna, which is now known as the Atlantic bluefin tuna. Pacific bluefin tuna can grow very large, reaching up to 3 metres (about 9.8 feet) long and weighing as much as 450 kilograms (about 990 pounds).

This tuna is very important to fisheries because it is caught in large amounts each year. For many years, there were too many fish being caught, and the group of fish nearly ran out. But in 2011, people started catching fewer fish to help them grow back. By 2024, checks showed that the fish group had recovered well. It is now seen as a good example of successful management. The Monterey Bay Aquarium's Seafood Watch program says Pacific bluefin tuna is a "Good Alternative" to eat.

Distribution

The Pacific bluefin tuna lives in the North Pacific, from the East Asian coast to the western coast of North America. It swims in warm ocean waters near the surface but can go deep.

These tuna breed in the northwestern Philippine Sea, near places like Honshu, Okinawa, and Taiwan, and also in the Sea of Japan. Some travel to the East Pacific and return to their breeding spots after a few years. They have also been seen in the Southern Hemisphere, such as near Australia, New Zealand, the Gulf of Papua, and French Polynesia.

This species is one group, or stock.

Physiology

Thermoregulation

Most fish are cold-blooded, meaning their body temperature changes with the water around them. But tuna, along with opah and mackerel sharks, are warm-blooded. This means they can control their own body temperature.

Tuna have special organs near their muscles called retia mirabilia. These organs help keep the tuna warm by moving heat from veins to arteries. This helps the tuna stay warmer than the water, giving them extra speed and power to hunt and travel far.

Life cycle

Pacific bluefin tunas grow until they are about 5 years old. They can reach around 1.5 meters (almost 5 feet) and weigh about 60 kilograms (130 pounds). They can live for 15 to 26 years. Some of these fish can get much bigger, up to 3 meters (almost 10 feet) long and weighing as much as 450 kilograms (about 990 pounds).

These tunas lay their eggs from April to August. The timing changes depending on where they are in the ocean. They eat many small fish and squids, and sometimes even other small sea animals like crabs and krill.

Human interaction

Commercial fishery

Pacific bluefin tuna are very important to many fishing industries.

Aquaculture

Japan is the leader in raising tuna in farms. Researchers there were the first to successfully raise baby bluefin tuna in 1979. By 2002, they had bred them, and by 2007, they did it again with the next generation. This farmed tuna is called Kindai tuna, a shorter name for Kinki University tuna.

Conservation

At first, Pacific bluefin tuna were not thought to be in danger, so they were rated as "Least Concern" in 2011. But by 2014, they were found to be at risk and were rated as "Vulnerable". Now, they are listed as "Near Threatened". A study in 2024 showed that their numbers have grown since 2010 because fishing rules have become stricter. The group that watches fish populations says they are now close to being safe, though they still need care.

Mercury levels

Main article: Mercury poisoning

See also: Mercury in fish

Pacific bluefin tuna meat can have substances like mercury that may not be good for people to eat too much of. This is a problem for some other tuna fish too.

Cuisine

Most Pacific and Atlantic bluefin tuna are eaten in Japan. This fish is especially good for sushi and sashimi and can be very expensive. The fatty part of the fish, called toro, is very special to sushi chefs. In Japan, eating bluefin tuna at the start of the new year is thought to bring good luck. Because of this, winning the first fish auction of the year gets a lot of attention and makes the fish cost even more. For example, in January 2013, a big tuna sold for a record price in Tokyo. Another big tuna sold for an even higher price in January 2019.