One hot evening last July, I visited the Michelin-starred unagi, or eel, restaurant Nodaiwa, which sits in a quiet basement beneath Tokyo’s glamorous Ginza shopping district. Next door is the world’s most famous sushi restaurant, Sukiyabashi Jiro, which was the subject of a documentary from 2012 called “Jiro Dreams of Sushi.” The restaurant is now so famous that a sign, written in English, sits outside its entrance, asking visitors not to take photographs. In recent years, less benign developments have forced Nodaiwa to place a sign at its entrance as well. Whenever I visit, I count myself lucky to find the following message written on it, in Japanese: “Today we have natural Japanese eel.” The restaurant started serving grilled eel out of a timber farmhouse, near the famous Tsukiji Fish Market, about two hundred years ago. And through five generations of continuous operation such a sign was unnecessary, even laughable, given the abundance of Japan’s native species of freshwater eel. But, in 2013, Japan’s government added Anguilla japonica to its official Red List of endangered fish, after researchers found that wild unagi populations had declined by about ninety per cent in the course of just three decades. At Tsukiji, wholesale prices for farm-raised unagi imported from China immediately surged to a record high of around forty U.S. dollars per kilogram, and remained there for much of 2013. Prices for the wild-caught, “natural Japanese” eels served at upscale restaurants like Nodaiwa climbed even higher, by as much as fifty or sixty per cent. But the government had been late to recognize the extent of the problem, which had already taken a toll on many famous restaurants specializing in kabayaki, a signature unagi preparation. In March, 2012, a year before the species was declared endangered, the beloved unagi restaurant Suekawa closed its doors, after sixty-five years of business, and it was followed a month later by the popular restaurant Yoshikawa. Then, in May of 2012, one of Japan’s best-loved kabayaki restaurants, called Benkei, closed its doors after more than six decades of serving eel in Tokyo’s historic “lower city.” The restaurants that survived were buying eels for ten times the price that they’d paid just eight years earlier, according to one vender at Tsukiji Fish Market. The family restaurant chain Hanaya decided to pull eel dishes from its summer menu. For other types of seafood, farm-raised stocks remain relatively stable when wild catches decline. But unagi, which hatch at sea but mature in freshwater, cannot be effectively bred in captivity, so farm-raised stocks rely on young eels, known as glass eels, which are harvested at sea, then raised to maturity at eel farms in China, Korea, and Japan. Overfishing of the glass eel is, undoubtedly, the source of the problem. Each year, Japanese people eat more than a hundred thousand tons of eel, which usually amounts to about seventy-five per cent of the total global catch. Roughly half of that annual eel consumption takes place during the summer months, when Japanese tradition holds that the nourishing unagi helps maintain one’s stamina against the withering heat. Eric Rath, a history professor at the University of Kansas who specializes in Japan’s culinary traditions, told me that this belief is “an idea that comes from the eighth-century ‘Collection of Myriad Leaves,’ the earliest collection of Japanese poetry and Japan’s most esteemed locus classicus for customs.” Grilled eel is so strongly identified with the midsummer months that it is the official food of a national holiday called the Day of the Ox. The crisis brought on by diminishing unagi catches is, therefore, multilayered: an environmental crisis for the endangered species and its habitat, a financial crisis for the centuries-old unagi industry, and a cultural crisis for the Japanese public. Scientists began researching the problem decades ago, long before the public could imagine unagi’s designation as an endangered species. At Japan’s Fisheries Research Agency, Hideki Tanaka has made some of the most significant breakthroughs in understanding the life cycle of unagi, but not without time-consuming setbacks: Tanaka’s team spent twelve years learning how to hatch artificially inseminated glass eels and keep them alive, only to find that all of the eels brought to maturity under laboratory conditions became males. The problem was eventually overcome by manipulating hormone levels in the animals’ feed, but this presented an obvious obstacle to controlled breeding. And with other obstacles preventing the widespread adoption of controlled breeding, some researchers are looking elsewhere for solutions. In late 2015, a university in Osaka announced a new effort to deal with the eel shortage. It was farming catfish with the aim of marketing it as a replacement for kabayaki eel, the most popular unagi preparation, which is made by slowly grilling cleaned and skewered eel over charcoal, dipping it repeatedly in a sweet and savory marinade made from soy sauce and mirin. In Tokyo, this preparation is typically served over rice with a light dusting of the powdered Japanese pepper called sansho. Then, in the summer of 2016, a popular daytime variety program invited a celebrity chef to show viewers how they could prepare kabayaki using freshwater fish as a substitute for unagi. “Maybe we don’t need to eat eel after all,” one presenter said as he tucked into his plate. Just a few months later, in September, the Standing Committee of the Convention on International Trade in Endangered Species convened in South Africa, where the prevailing mood suggested that the European Union may back a moratorium on eel harvesting, which could take effect in three years if it passes. This could, in theory, restrict the flow of European glass eels to Chinese farms that raise eels primarily for the Japanese market. But it’s hard to imagine that such a move would accomplish much more than increasing demand for glass eels caught in the U.S., where, in 2013, Maine fisherman caught eighteen thousand pounds of the tiny creatures for export to Asia, bringing in about thirty-three million dollars. Then there’s the matter of illegally harvested and traded specimens. Last April, a report by the Japanese news agency Kyodo claimed that Japan was circumventing regulations meant to curb overfishing by importing vast quantities of glass eels from Hong Kong. And, despite broad public curiosity about unagi alternatives, Tokyo supermarkets reported that sales of prepared kabayaki meals climbed ten per cent year-on-year last July, despite the fact that one of the most popular retailers had raised its prices by about three U.S. dollars per serving. The Day of the Ox fell on July 30th in 2016, and for weeks beforehand the convenience stores and supermarkets in my west Tokyo neighborhood distributed full-color flyers advertising various kabayaki sets that could be ordered in advance for between ten and thirty U.S. dollars. One such advertisement declared unagi “the irresistible flavor of summer.” Though I had not been able to resist my annual visit to Nodaiwa earlier in the summer, I opted for a less traditional meal on the day when unagi consumption reaches its peak: for the first time, I celebrated the Day of the Ox with catfish kabayaki. Although it is popular as a summer dish, unagi is actually at its most delicious in December, after it has grown fatter to protect itself against the cold of winter. And despite my willingness to experiment with substitutes, there’s nothing like the real thing when the real thing is at its best. So, when I arrive in Tokyo for the holidays after several months away, I have no doubt that I will head straight to Nodaiwa, as usual. The sign out front will tell me everything I need to know.