A woman looks at head of bluefin tuna on display in front of a store at Tsukiji fish market in Tokyo, Monday, February 19, 2018. The large bluefin are particularly valuable in Japan, where they are considered a premium sushi and sashimi fish. A single fish sold for more than $1.75 million at an auction in Japan in 2013. (Photo by Koji Sasahara/AP Photo)

Kiyomura Co's President Kiyoshi Kimura (C), who runs a chain of sushi restaurants Sushi Zanmai, poses with a 212 kg (467 lbs) bluefin tuna at his sushi restaurant outside Tsukiji fish market in Tokyo, Japan, January 5, 2017. Kimura won the bid for the tuna caught off Oma, Aomori prefecture, northern Japan, with a 74 million yen (633,000 USD) at the fish market's first tuna auction this year. (Photo by Issei Kato/Reuters)

Visitors look at tropical fish transported from Japan's southern island of Okinawa displayed in a giant 14-ton fish tank at the Sony Square event space in Tokyo on July 17, 2016. The 45-day-long summer exhibition will be held through August 28 to display sea creatures common to the waters around Okinawa. (Photo by Kazuhiro Nogi/AFP Photo)

Ryo Minemizu, one of Japan’s emerging stars in the field of marine life photography and the 2017 winner of the Nikkei National Geographic photography prize, captures the beauty and complexity of plankton that drift in our planet’s oceans and other bodies of water in meticulous detail. Here: Batesian mimicry by a Soleichthys fish larva. (Photo by Ryo Minemizu/The Guardian)

A eight-metre-long Whale shark swims with other fish in a worlds' largest tank with its front panel size of 8.2 metre x 22.5 metre at the Okinawa Churaumi Aquarium on February 26, 2010 in Motobu, Okinawa, Japan. Japan's most popular aquarium attracts more than 2.5 million visitors per year. (Photo by Koichi Kamoshida/Getty Images)

A humpead wrasse, transported from Japan's southern island of Okinawa, swims with other tropical saltwater fish on display in a tank for the Sony Aquarium 2017 exhibition in Tokyo on July 31, 2017. The Sony Aquarium 2017 exhibition, featuring marine life common to the waters around Okinawa, runs until August 13. (Photo by Kazuhiro Nogi/AFP Photo)