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Category: Preserved Fish

Kusaya made from Kusayamoro (Mackerel scad) and Hamatobiuo


Kusayamoro (scientific name Decapterus macarellus), has many local names in the Japanese islands: shakkari (Koudu Island), aumuro oomuro boomuro (large fish: Izu archipelago, Ogasawara archipelago). Usually it is called also muroaji because it is a fish of the muroaji genus but the common name in the islands near Tokyo is kusayamoro, derived from the local name aumuro and the traditional preservation method kusaya. The body is flat and spindle-shaped. The back of the body is a deep blue color and its abdomen is silvery-gray. There is a blue band running along the center of the body’s side, which connects the fish’s head to its tail. It has two distinct dorsal fins, one chest fin, and one stomach fin, all of which are separated by a soft fluid lining. The Kusayamoro grows to be approximately 50 cm long. 

The Hamatobiuo (scientific name Cheilopogon pinnatibarbatus japonicus) has a long and thin, spindle-shaped body. The lower portion of its abdomen is narrow, while the cross section of the center portion of its body resembles an inverted triangle. It has one dorsal fin, one abdominal fin, and one very large fin near its chest. The lower tail is longer than the upper tail. The scales of the fish are very large, so they are easy to remove. The Hamatobiuo’s back section is deep blue and its underbelly is white. Its breast fin is nearly transparent. The fish’s siding runs along the lower side of its body and grows to approximately 50 cm. The Hamatobiuo migrates to the Izu archipelago during spring to lay eggs in large quantities. For this reason, the Hamatobiuo has been given the name, “Spring Tobi” (tobi = hawk) or “Spring Fly”. Historically spring was the season for laying eggs, so the Hamatobiuo were especially abundant during that time of year. Large quantities of these fish, however, were caught by net fishermen who placed long nets in the pathways of the fish and pulled them up once they were stuck. The fishermen would then hand-remove the fish one tail at a time. Traditionally, when the fishing was complete at night, the fisherman would stack his catch so that the soup could be offered to his crew for breakfast as an expression of appreciation for their labor. In preparing his own lunch for the following day, the fisherman would be sure to avoid all foods that had vinegar—including sushi and pickled vegetables—because the Japanese word for “vinegar” sounds identical to the word for “bad catch.” 

During the Edo period (1603 - 1867) near Tokyo, particularly the Izu archipelago where the strong Kuroshio current helped bring in many schools of fish, many families relied on fishing for their living. Every island adopted a unique culture of eating fish and salt was a very valuable resource, for not only was there a limited supply, but inhabitants of the islands also used it to pay annual land taxes. In order to conserve this rare commodity, families would repeatedly soak the fish in their juices as a means of preservation. Kusaya, which sounds similar to the Japanese word for “ill-smelling” was the method of preparation for Kusayamoro and Hamatobiuo in Hachijo Island during the Edo period. The fishermen would season the kusaya with soy sauce and call it “island sushi.” Island sushi, Hamatobiuo soup, kusaya are all part of the important ceremonial festivities on the island, and the unique fragrance of the Kusayamoro juice and the deep flavor it provided was highly regarded in comparison to ordinary marine products in the area. However, the changing lifestyle and culture due to modern housing and construction has contributed to a simultaneous depletion of the rich flavors and kusaya consumption. Even in Hachijo Island and Niijima Island, where kusaya production was traditionally strong, the younger generations are not following the fishing traditions of their ancestors. Nonetheless, there are still people who work hard to obtain the quality raw materials needed for processing and manufacturing fish products. Kusayamoro is also used to produce Murobushi. Slow Food Tokyo Bay has planned local tours and fishing experiences for students, as well as a tasting sessions.



The sun-drying method for cooking fish originated in the Edo era, when inhabitants of the Izu archipelago repeatedly soaked fish in brine as a means of preservation. However, it is believed that eating “kusaya juice” came from the idea that harmful germs and bacteria would not accumulate throughout the repetitive soaking of fish in brine.

Traditional processing method

1. The fish is opened manually and its internal organs removed

2. The fish is butterflied and washed thoroughly with water

3. The fish soaks in its own kusaya juice for 8~20 hours

4. Using a porous basket, the juice is removed

5. The fish is again rinsed with water, thereby extracting the salts

6. The fish is sun-dried for 1- 2 days

The fish has a salty flavor and unique aroma, but is mellower than most typical dried fish. The fish is roasted lightly and eaten in dishes dressed with sauce, tea, etc. Not much has changed since the Edo period. The task of opening the fish is now mechanized and drying is now achieved by applying cold air in a dry room, but the biology of the food has not been altered. Kusayamoro is especially popular because it is fished fairly—despite lower yields, fishermen use the “stick receiving net” to catch these fish, as opposed to the “round haul net” method, which is used for most other large-scale fishing operations. This method of fishing, which uses fish detecting equipment, began after the war. When the equipment signals fish underwater, the fisherman prepares a net on the left side of the boat and throws firewood feed into the surrounding waters. This attracts the muroaji, who then crowd in the boat’s vicinity. In order to ensure that as many fish get caught in the net as possible, the boat is repositioned and the fisherman quickly hauls the net in. It usually takes 7 fishermen to operate one boat. In comparison to mass capture fishing methods, stick receiving net fishing is far less destructive, which means the quality of the yield is often very high. 

However, with the decrease in consumption of kusayamoro, such fishing industries and fishing methods have begun to disappear, as well. Several million Hamatobiuo were fished annually, but those numbers dropped severely by the second half of the 1980s. No Hamatobiuo were caught in 1990. Because of this, members of the Marine Agriculture and Forestry Center on Tokyo Island enforced restricted fishing allowances, so as to protect the quantity of Hamatobiuo in the area. Several investigations were put into place following this drastic decline and Tokyo marine products personnel began restricting the legal capture quantity. Through the efforts of the Marine Agriculture and Forestry personnel and the approved catch (TAC) regulations, several hundred thousand units of fish have recovered in recent years. Tokyo authorities have implemented strict regulations that prohibit fishermen from overfishing Hamatobiuo. In an attempt to prevent depletion of resources, all fishing equipment must comply with length/weight/size restrictions. Hamatobiuo counts from 1996 showed a slight recovery (a few hundred thousand units), but authorized personnel have decided to continue limiting Hamatobiuo fishing, for their numbers are still vulnerable to year-by-year fluctuations. Limits are reset every year, based on the data of the previous year. According to resource management, recent capture levels have been stable. However, since the Hamatobiuo are migratory fish, annual capture rates in the future are expected to fluctuate. In light of competition with other fish and marine life, the price and consumption of Hamatobiuo has simultaneously fallen. If the decreases in capture and price continues, the Hamatobiuo, whose processing requires significant human labor, could be seriously endangered. In recent years, decreased kusaya consumption has led to falling prices, which has further contributed to a drop in the number of people working in the fishing industry. However, the traditional fishing industry in the Izu archipelago, long referred to as the kusaya production capital, is still relatively healthy. Local raw materials are the source of 226 tons of kusayamoro production (2006), 63% of which are used for broth. Information about kusaya must be spread within and outside the island because it is difficult for the younger generation to develop the habit of eating kusaya.

Kusaya is now produced in Niijima Island, Hachijo Island, and the Izu large islands (Tokyo prefecture) but the traditional production area was the entire Izu archipelago. Historically, the Hamatobiuo made their way to Hachijo Island by way of ocean current in the adjacent waters of Kuroshio. In Japan, production occurs in the Pacific Ocean between the Eastern-Sea area and the Amami archipelago, and is distributed around the Izu and Ogasawara archipelagos but now Hamatobiuo fish are very rare in Ogasawara.

Boarded in 2010

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