Japan should abandon its love affair with sushi and embrace a diet from the austere days of the past, according to the country’s leading fisheries expert.

Masayuki Komatsu, a long-serving minister in the fisheries agency and now head of a prominent think tank, said that Japanese urgently needed to accept that bluefin tuna, of which they consume 44,000 tonnes every year, would soon be far beyond the budgets of ordinary people as stocks dwindle and prices soar.

Sushi in general must become a dish served only on special occasions, he said, and the days of Tokyo restaurants serving a generous helping of raw bluefin on a bed of rice for about £5 must end.

Professor Komatsu blamed Japan’s all-powerful trading houses for encouraging people to become blasé about cheap bluefin, an attitude that has led to the collapse of worldwide stocks and growing fears of extinction.

The comments coincide with rising clamour for a ban on the international trade in bluefin tuna, a global market in which Japan buys about 80 per cent of every catch from the Atlantic and Mediterranean. Japanese restaurants serving bluefin tuna worldwide have been targeted by protesters.

Britain, the United States, France and Germany are supporting a campaign — led by the principality of Monaco — for a ban. The moratorium would work by adding the bluefin tuna to those animals listed under the Convention on International Trade in Endangered Species, a panoply of 5,000 animals and 28,000 plants that includes the red panda, aardwolf, pangolins, whales, seahorses, even the probably extinct thylacine, or Tasmanian tiger. A proposal is expected to be finalised in the next couple of months and may be ratified at a conference of the convention in Qatar next March. Washington may draft its own proposal for a ban on bluefin trade.

It is expected that Japan will fiercely resist such a move and rally a diverse mix of supporters to its cause, as it has on the issue of commercial whaling bans. The official line from Japan’s fisheries agency is that any curbs on the international tuna trade should be discussed in a different forum. Nevertheless, government sources say that many MPs already accept the need for worldwide tuna stocks to be rebuilt.

Professor Komatsu dismissed the idea that the Japanese taste for sushi deserved special protection. “The habit of eating such a valuable tuna in a casual setting is a very recent phenomenon, which only really dates back to the start of the Heisei era [1989] and the popularity of conveyor-belt sushi from that time,” he said.

In the 1960s and 1970s, he added, sushi and sashimi were eaten only on rare “sunshine days” a couple of times each year, a practice that may be forced on Japan by the outside world if it does not adapt to the new market realities of its own accord. If the sushi habit proves too hard to kick, Japanese should wean themselves off bluefin by returning to more local fish, such as sardines and Alaskan pollock, he said.

Meanwhile, Japanese scientists are engaged in a huge research effort to cultivate bluefin tuna from birth to maturity in farm conditions, a process previously thought commercially impossible. Indeed, one institute claims that it has managed to engineer the progress of 100,000 eggs to the next stage of maturity.

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