A bluefin tuna has fetched 74.2m yen (£517,000) at the first auction of the year at Tsukiji market in Tokyo, amid warnings that decades of overfishing by Japan and other countries is taking the species to the brink of extinction.

The 212kg fish, caught off the coast of Oma in northern Japan, was bought by Kiyomura, the operator of the Sushi Zanmai restaurant chain, after its president, Kiyoshi Kimura, outbid rivals for the sixth year in a row.

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The first auction of the year at Tsukiji always attracts high bids from restaurants hoping to turn the publicity associated with the event into a marketing opportunity. Kimura’s bid, which works out at 350,000 yen per kilogram, is the second highest since the market started keeping records in 1999. The 155.4m yen Kimura paid for a bluefin in 2013 is the highest bid ever recorded.

At the price he paid on Thursday, a single piece of fatty tuna sushi would cost about 25 times the 400 yen his dozens of restaurants usually charge for the same cut.

Kimura, whose bids have earned him the nickname “tuna king”, said the fish was “a bit expensive, but I am happy that I was able to successfully win at auction a tuna of good shape and size”.

Kimura added he was looking forward to serving it at his restaurants. “I want everyone to taste this delicious tuna,” he said as he posed with his prize bluefin.

Facebook Twitter Pinterest A tuna displayed at Tsukiji wholesale fish market on Thursday during the first auction of 2017. Photograph: Aflo / Barcroft Images

Conservationists said the publicity surrounding the auction risked overshadowing the plight of the Pacific bluefin tuna. They have called for a two-year moratorium on fishing to rescue the Pacific bluefin population, which is estimated to have plummeted by 97% from its historic high due to decades of overfishing.

“People should be thinking about that when they see news about the auction,” Jamie Gibbon, officer for global tuna conservation at the Pew Charitable Trusts, told the Guardian.

Last month, 25 tuna-fishing nations plus the European Union agreed on the need for an urgent bluefin tuna recovery plan, but Japan is expected to resist drastic cuts in catch quotas or a moratorium to give stocks the opportunity to recover.

About 70% of Pacific bluefin are less than a year old when caught, according to Gibbon, and 95% are caught before they reach three years old – a practice that damages the species’ ability to reproduce.

The Western and Central Pacific Fisheries Commission tightened international limits in 2015 as the species remained under threat, halving the catch of bluefin tuna under 30 kilograms from the average caught between 2002 and 2004.

“If fishing continues at its current rate, then Pacific bluefin stocks will fall to levels that are commercially unsustainable, but Japanese officials continue to say that catch reductions will place too big a burden on fishermen,” Gibbon said. “Short-term profits are being put ahead of long-term conservation.”

Facebook Twitter Pinterest Buyers inspect frozen tuna at Tsukiji wholesale fish market on Thursday. Photograph: Aflo / Barcroft Images

About 80% of the global bluefin catch is consumed in Japan, where it is commonly served raw as sashimi and sushi. A piece of otoro – a fatty cut from the fish’s underbelly – can cost several thousand yen at high-end restaurants in Tokyo.

The global popularity of Japanese food is fueling an appetite for bluefin in other countries, including China.

Thursday’s auction could be the last at Tsukiji, whose planned relocation to more spacious premises at the end of last year has been delayed by at least 12 month, and could be scrapped altogether. Tokyo’s governor, Yuriko Koike, delayed the move due to concerns over soil and air pollution at the new market, which stands on the former site of a gas plant.