Bluefin tuna is expensive because it’s in such high demand in Japan. According to “Why Tuna's Both Cheap and Expensive, Plentiful and Very Endangered,” a bluefin tuna caught off Long Island goes straight to Japan, where a 500-pound fish can sell for as much as $1.8 million.
The popularity of bluefin tuna has skyrocketed since the 1950s because fishermen starting using nylon nets. Huge pelagic fish, bluefin tuna are incredibly strong and can destroy nets and swim off. Stronger nets meant that fishing fleets could harvest bluefin without losing the entire catch.
The largest and most fatty tuna fish, bluefin is in such high demand in Japanese sushi restaurants that chefs and restaurateurs go to tuna auctions to bid on fresh-caught bluefin. As of 2015, a large bluefin was going for $50,000 to $70,000 in Japan, meaning most American markets can’t compete. As Japanese demand increases, fewer bluefin reach breeding age, potentially significantly reducing populations through over fishing. Should bluefin populations crash, prices could skyrocket again.
To improve breeding stock and keep a steady supply of bluefin, tuna “ranchers” and other aquaculturists are working to establish sea farms where schools of tuna are raised in the open ocean and then herded to market.