Tuna are awesome. We don’t get to say that enough, so since it’s World Tuna Day, I want to make amends. These fish are majestic ocean wanderers, who have earned their place in history, but today they are sadly the icons of global overfishing & dodgy fishing methods, and a globally-traded commodity.
There are 8 recognised species of ‘true’ tuna (Atlantic bluefin, Pacific bluefin, southern bluefin, bigeye, yellowfin, albacore, longtail & blacktail) and a further 8 species in the extended family that are normally called ‘tuna’.
Skipjack, the most commonly-eaten tuna is not biologically a proper tuna, it’s more of a distant cousin.
Big tuna are super-predators. They eat fish that eat fish, so they are a few steps up the food chain. That makes them comparable with tigers, or wolves on land. Being high up the food chain has its disadvantages – it also means that the bigger species like bigeye and bluefin also accumulate more toxic chemicals, most notably mercury.
Bluefin tuna are also called ‘red tuna’ because of the colour of their flesh. It’s red because it’s oxygen-rich. These fish are effectively warm-blooded, and regulate their temperatures.
Being warm blooded means that bluefin can live in cooler waters - being big also helps deal with cooler climates.
Bluefin are fast. They can accelerate quicker than a sports car, which is a force to be reckoned with when a fully-grown bluefin can be 3 metres long or more.
The front fins on a tuna 'fold down', tucking into handy grooves and making them more hydrodynamic - perfect when the tuna feel the need for speed.