Tuna
Depth: 100 m · Sunlight Zone
The tuna is a sprinter of the open ocean and one of the fastest fish of all. Unlike most fish it keeps its body warm, which keeps its muscles strong and fast. It swims almost without pause its whole life.
For scientists
Tuna are regionally endothermic: through a wonder-net of blood vessels (rete mirabile) they keep their muscles, eyes, and brain warmer than the water and so stay powerful and fast. Their crescent tail and fins that fold into grooves make them extremely streamlined. They must swim constantly to drive enough oxygen over their gills through the open mouth.
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