Tuna

These large marine fish live in shoals, and they are capable of swimming through the oceans at high speed, with their body shapes and special biology designed to match their athletic lifestyles.

The body of a tuna is like a spindle; in other words, it is tapered at both ends. This shape allows the fish to cut through the water with little resistance. It means that the fish uses less energy when swimming; particularly as its entire body, including the fins, are streamlined. Furthermore, the swimming muscles are deep within the fish’s body, not just under the skin as in other fish. This arrangement prevents the tuna’s body from flexing from side to side as it swims, which also helps it swim very efficiently.The tuna’s swimming behavior appears almost effortless, even when they accelerate in quick bursts.

Warm-bodied Fish

Unlike most other fish, tuna can keep their body temperature higher than that of the water in which they are swimming. This helps their muscles to work better. It also gives them a great advantage when chasing prey whose body temperature depends on the temperature of the sea around them. Tuna are able to achieve this feat thanks to an unusual arrangement of blood vessels, known as the rete mirabile. It works by transferring heat from one set of blood vessels to another. Cold, oxygen-rich blood from the gills is channeled so that it passes very close to blood vessels carrying much warmer blood from the depths of the body. This warms up the cold blood before it flows to the fish’s muscles, making them work better.