Atlantic bluefin tuna

The Atlantic bluefin tuna is a huge, sleek, silvery-blue fish built for speed. It lives in the Atlantic Ocean and the warm Mediterranean Sea, swimming from the coasts of Europe and North Africa all the way across to North America. Bluefin tuna are travellers, and they can cross whole oceans on their long journeys.

These are some of the biggest bony fish in the sea. A grown bluefin is usually about two to two and a half metres long — longer than a bed — and can weigh as much as a large horse. The very heaviest one ever recorded weighed around 680 kilograms, which is heavier than a piano.

Bluefin tuna have an amazing trick: they are warm-blooded in a special way. They keep the muscles inside their bodies warmer than the cold water around them. This warm engine lets them swim fast and far, chasing food even in the chilly waters of the North Atlantic where many other fish would slow down.

Tuna are carnivores and clever hunters. They race after smaller fish like herring and mackerel, and also eat squid and other small sea creatures, often hunting together in groups. A mother bluefin can lay a giant number of tiny eggs — up to about 40 million at a time — floating out into the open sea.

Long ago, so many bluefin tuna were caught that people worried about them, but fishing limits have helped their numbers climb back up. Today they are listed as least concern, which is happy news. Looking after the ocean and keeping fishing fair will help these fast, powerful swimmers thrive for years to come.