THE heat-induced fatigue that strikes millions during Japan’s high summer is known as natsu-bate. A popular antidote is grilled eel, drenched in a sweet sauce and often served on a bed of rice. Rich in vitamins, protein and calcium, the restorative powers of the oily treat are eulogised in popular television shows. Yet unfortunately for Japan, the main ingredient is running out.

Overfishing has wrought havoc with global stocks of eels, prompting America to recommend that several species of eel be put on an international endangered list. That was front-page news in Japan. Greenpeace listed species of eel as endangered two years ago, joining sharks, bluefin tuna and Atlantic cod.

Japan consumes seven-tenths of the global eel catch and is now feeling the heat. Wholesale prices have doubled this year and dozens of eel restaurants across the country have closed. “We can’t pass on that sort of price rise to our customers, so we’ve been forced to absorb most of it ourselves,” said Danzo Yamamoto, manager of Unatetsu, one of central Tokyo’s best-known eel restaurants. “But how long can we do that for?”

In four decades, stocks of Japanese eels have fallen by nine-tenths. Japanese wholesalers turned first to European eels. But they are now on the watchlist of the Convention on International Trade in Endangered Species (CITES). Among other things, the Atlantic eel is highly susceptible to a parasitic nematode introduced when stocks of the Japanese eel were imported to Europe for aquaculture. Japanese suppliers then shifted to farm-bred eels from China and South Korea. Eel farms, however, still depend on elvers netted from the wild, putting further pressure on populations.

Eels spawn only once in a lifetime, in a complex and still little-understood cycle. So until farmers learn how to raise adults from eggs at a commercially reasonable cost, Japan will have to adjust to eating a lot less. Meanwhile, desperate Japanese wholesalers now flock to the Philippines, Indonesia and even Madagascar to keep the nation’s summer tables stocked.

Suppliers are trying to stay one jump ahead of the endangered listings. The East Asia Eel Resource Consortium, a group of industry and research representatives from Japan, China, South Korea and Taiwan, has called for an Asia-wide system of statistical measurement. But conservationists argue that self-regulation will only push the eel faster towards extinction.

It all sounds familiar. Two years ago the Japanese government helped torpedo a CITES attempt to ban trade in Atlantic stocks of bluefin tuna, a sushi mainstay. Japan is also likely to lobby against a trade ban in eels, arguing instead that industry-led bodies and not conservationists can best manage sustainable stocks. Perhaps so. But if that assessment is wrong, millions of Japanese may soon have to look elsewhere for their summer culinary boost.