Bluefin tuna (Thunnus thynnus) is one of the largest and most valuable species of tuna, often referred to as the “ruby of the sea.” It is mainly distributed in the western and eastern Atlantic Ocean, as well as the Mediterranean Sea, with some populations also found in the Pacific. Bluefin tuna are large and muscular, with adults reaching lengths over 3 meters and weights exceeding 600 kilograms. Known for their incredible speed, they are highly migratory and powerful swimmers.

The flesh of the bluefin tuna is bright red and rich in high-quality protein, DHA, and EPA, making it extremely nutritious. Its fat is evenly distributed, especially in the "chūtoro" (medium fatty) and "ōtoro" (high fatty) sections, which are tender, buttery, and melt in the mouth. These cuts are considered the finest ingredients for premium sushi and sashimi, highly sought after by gourmets around the world.

Due to overfishing, wild bluefin tuna populations have been severely depleted, leading to strict international regulations and the development of aquaculture methods to protect wild stocks. Japan is one of the largest consumers and traders of bluefin tuna, with record-breaking auctions at Tsukiji and Toyosu markets highlighting its rarity and value. Bluefin tuna represents not only the pinnacle of fine dining but also a critical issue in sustainable ocean resource management.