Thunnus is a genus of large, fast-swimming fish commonly known as tuna. They are found in warm seas around the world and are known for their streamlined bodies, which allow them to swim at high speeds. Tuna are important both ecologically and economically, as they are a key species in marine food webs and are highly sought after in commercial fishing. There are several species of tuna within the Thunnus genus, including the bluefin tuna, yellowfin tuna, and albacore tuna. These fish are characterized by their strong muscles and ability to regulate their body temperature, enabling them to thrive in various oceanic environments. Tuna are also popular in culinary dishes, particularly in sushi and sashimi.