Photo/Illutration Sushi topped with “untapped fish” is served at Osakana Club Hama, a restaurant in Kashiwa, Chiba Prefecture. (Masakazu Higashino)

Regulars of a sushi restaurant at a university research institute in Chiba Prefecture may be familiar with the “neta” (toppings) on the rice, but newcomers could be left scratching their heads.

“Yumekasago” (blackbelly rosefish), “goso” (gephyroberyx darwinii) and “ginmatou” (zeus faber) are just a few of the fish available for “nigiri” (hand-rolled) sushi at Osakana Club Hama.

These “untapped fish” for neta are the main reason why an increasing number of sushi lovers have been drawn to the restaurant.

For a long time, fishermen have generally tossed these by-catch fish back into the sea largely because they are unfamiliar to chefs and diners and are often difficult to keep fresh.

The untapped fish that are brought into shore are usually sold at local fish markets at cheap prices.

But these fish are losing their obscurity.

Restaurants and consumers are increasingly learning that untapped fish can taste as good as the fish typically used for sushi neta and other common dishes.

A variety of methods are now being deployed to prevent untapped fish from going to waste and to increase the income of fishermen.

Osakana Club Hama is located on the campus of the University of Tokyo’s Atmosphere and Ocean Research Institute in Kashiwa, Chiba Prefecture.

Every morning, Hiroyasu Hama, the 76-year-old owner of the restaurant, receives calls from fishermen and intermediary wholesalers around the nation about “ultra-rare fish” in their possession.

Of the various untapped fish delivered to the restaurant, Hama gets to decide which ones to use each day.

On a shelf at the restaurant, Hama keeps a file of photographs of the fish in case he needs to check what exactly he is serving.

Hama started preparing untapped fish at the restaurant almost 30 years ago, when he noticed that obscure fish and small-sized specialty species were being sold at fish markets at sharply reduced rates.

He said he has cleaned at least 700 types of fish so far.

The restaurant had long been relatively unknown to the world outside the university campus.

But nowadays, more customers outside of the university, mostly women, are flocking to the restaurant to taste the rare sushi.

“There has been a growing interest in untapped fish,” Hama said.

He said he is worried that the prices of these fish “will increase because everybody wants to eat them.”


The growing popularity of untapped fish is particularly noticeable in the northeastern Tohoku region of Japan.

Along the Sanriku coast, a prominent fishing ground, “donko,” also known as “ezoiso-ainame” (brown hakeling), has been in high demand.

The freshness of the deep-water fish deteriorates quickly, so it is usually traded at local markets for bargain prices and is rarely distributed to distant locations.

But over the past several years, people from afar have been traveling to the Tohoku region to taste donko.

At Zensukeya Shokudo, a restaurant in Miyako, Iwate Prefecture, the most popular dish is now large, deep-fried donko fillets served on a bowl of rice with salty-sweet sauce and a soft-boiled egg.

At Wakou, an izakaya (Japanese-style pub) in Kamaishi in the prefecture, customers love eating donko either deep-fried or finely chopped.

Kazuyuki Fujii, 73, the pub owner, welcomes the trend.

“The catches for salmon and saury have become lean,” Fujii said. “Thankfully, I can serve donko in abundance at a reasonable price.”


Recent poor hauls of major fish species have been a driving force of the wider distribution of untapped fish.

The trend has expanded to e-commerce, as younger generations in the fishing industry are increasingly seeing the value of the by-catch.

Fish Door, a company of young fishermen in Happo, a northwestern coastal town in Akita Prefecture, in 2022 started selling untapped fish on Tabe Choku, a major farm-to-table online shopping site.

The northern prefecture is known for its specialty “hatahata” (sandfish). But catches have been poor for a long time.

The young fishermen hope to breathe new life into the region by selling untapped fish online to consumers nationwide.

Fish Door member Hokuto Chiba, 37, said many fish that have been caught are not sold at markets because they lack the size or quantity.

They are flavorful, but there are just too many for the fishermen themselves to bring home and eat.

“It’s a shame to waste them,” he said he has long thought.

For the Tabe Choku project, the company came up with a 2-kilogram package, named “fishermen’s share,” containing around 10 kinds of untapped fish caught off the coast of Akita Prefecture. One package costs 2,000 yen ($15), plus shipping fees.

It includes “hokke” (Okhotsk atka mackerel), “nodoguro” (hilgendorf saucord) and “kanagashira” (gurnard).

It caused a sort of feeding frenzy.

“I am so happy to see so many fresh fish packed together,” a satisfied customer commented.

“I appreciate that it’s only 2,000 yen with this many fish,” another said.

After the package was shown on a nationwide TV broadcast, the company was swamped by even more orders.

“I am happy that people enjoy eating these fish that used to be dumped,” Chiba said.

At one time, staff got overly excited and stuffed more than 2 kg of fish in the packages. The company received a “complaint” about “too many fish,” Chiba said, laughing.

A representative of Tabe Choku said more fishermen are selling their untapped fish on the site.


The city of Ishinomaki, Miyagi Prefecture, started a study on untapped fish in fiscal 2019.

Bottom trawling is a common way to fish off the coast of Kinkazan in the city, and “tara” (cod) and “kichiji” (broadbanded thornyhead) are local specialties that fetch high prices.

Less-familiar fish are also pulled up from the sea bottom, but they are considered unsellable, and 30 to 40 percent of the deep-sea catch is usually dumped.

Hidekatsu Suzuki, an associate professor at Ishinomaki Senshu University, has led the study with the city to seek ways to effectively use these untapped fish and bolster fishermen’s income.

“Deep-water fish have many different possibilities,” Suzuki said.

One method to reduce waste is to create processed products from these fish.

Suzuki said kanagashira, a white-meat fish that resembles “houbou” (sea robin), is an up-and-coming untapped fish.

He said kanagashira remains fresh even after being kept in a fridge for two days, and it tastes great as sashimi.

The annual catch of kanagashira is about 300 tons in Ishinomaki, Suzuki said.

The eel-like “nagatsuka” (long shanny) is another promising untapped fish, Suzuki said.

The fish spoils quickly, so sashimi is not an option. But broiled nagatsuka is delicious, he said.

Suzuki said the research team is also looking for ways to use untapped fish in medicine and supplements, in addition to producing a material that can be used in plastics.

“I hope the study contributes to the revitalization of Ishinomaki,” he said.

(This article was written by Masakazu Higashino and Atsushi Hara.)