The Toyosu Market in Tokyo is a 4-million-square-foot area for squid, mackerel, and most famously, tuna. The market is home to world-renowned tuna auctions, where expert bidders bet millions of dollars on top-tier tuna. But the population of tuna is on the decline, specifically bluefin tuna, which is known as the king of sushi. Business Insider follows expert bidder Takayuki Shinoda inside the fast-paced world of tuna bidding and its role in marine life sustainability.