What is Japanese Grunt Fish (aka Isaki)?

Isaki sushi and sashimi are the two most popular food items in Japan. Their complex taste and tender texture can make anyone’s mouth water. This delicacy is usually enjoyed at Japanese sushi restaurants.

Not many people are familiar with Japanese grunt fish, but it should be on the bucket list of any food enthusiast. Moreover, the process of preparing Isaki is complex. There are several ways Japanese grunt fish is prepared and consumed. But, let’s first talk about what the Japanese grunt fish is, where it is found, and what season is best for eating it.

What is Japanese Grunt Fish?

Japanese grunt fish, also known as chicken grunt, Threeline grunt, and Isaki, belongs to Perciformes (an order or superorder of ray-finned fish). An adult Isaki can grow up to the length of 40 cm.

Grunts tend to swim in flocks, and their diet usually consists of small fish and crustaceans. Although Isaki is classified as a white-fleshed fish, the color of its flesh has a red hue to it. 

It is a common practice to age Japanese grunt before eating to make the texture and taste better. Isaki has gained popularity in recent years as it is an ingredient in many types of sushi. Isaki dishes are well-liked by fish lovers, thanks to their taste and texture. It is especially popular among white meat fish enthusiasts.  

Where are Japanese Grunt Fish Found?

Isaki can be found in the coastal areas of Japan as well as in enclosed bays. It usually inhabits the warm currents in the southern parts of Japan. The locals and the tourists enjoy this delicious fish. 

Most restaurants get their Japanese Grunt fish from Kyushu Island.

What is the Best Season for Eating Japanese Grunt Fish?

Isaki retains its flavor even during spawning seasons while carrying eggs, unlike many other fish species. This means you can eat Isaki sushi or sashimi even during summer (the spawning season of Japanese grunt fish). 

But what is the best season for eating this fish? Generally, summer is considered the best season for enjoying Isaki. Isaki fish caught between June and July are considered the most delicious. During these months, they are much fattier and tastier. This increase in fat makes the texture and taste even better. Food lovers enjoy the fatty taste, making Isaki an especially popular food item during summer in Japan.

The arrival of Isaki in Japanese restaurants is a sign of the start of the rainy season. Japanese grunt fish caught between June and July is called “Tsuyu Isaki,” translating to “rainy season grunt.” 

Preparation of Isaki Fish

Several methods are used to prepare Isaki fish, but the most popular one is aging it before consumption. Doing so brings out the flavor in the flesh, making it more delicious. Most restaurants age their Isaki to bring out its flavor. 

Given below is a brief overview of how Isaki is prepared: 

1. Ikejime

To properly age an Isaki fish, it needs to be killing using the Ikejime technique. Ikejime technique refers to the process of making a slight cut at the tail of a fish after it is killed. Doing so allows the blood to flow out. This is a necessary step for the aging of an Isaki fish.

2. Descaling the Fish

Next, the Isaki fish is washed in cold water to start with descaling. During this step, the scales are removed from the fish. It is good practice to have a stream of cold water running onto the fish while descaling. Doing so helps the scales and slime wash away. There are many tools that can be used to descale a fish. Whichever tool you choose, the scaler should be run against the direction of the scales for the best results. 

3. Removal of Guts and Gills

Finally, the guts and the gills are removed with a sharp knife. This process is necessary as these organs can start to rot while aging if they are not removed. Anything that can rot during the aging process can spoil the whole fish. Ensure that the Isaki is completely clean once you have removed the guts, gills, and air-bladder. 

As a sharp knife is used in this step, one should ensure their safety and be careful while cutting.

4. Aging the Isaki Fish

The fish is now prepared for aging. A paper towel is placed inside the head and stomach cavities of the fish. During the aging process, the paper towel absorbs excess blood. 

Next, the Isaki is placed in a plastic bag from which the air is then removed. The opening of the plastic bag is tied up to prevent any air from entering. 

The fish can now be placed in a fridge to be aged for 1 or 2 days. 

5. Filleting of the Isaki Fish

Once the Isaki fish has been aged, it can be filleted. The spine, pin bones, head, tail, etc., are removed during this step. The end product is a set of perfect Isaki fillets.

Skin is also removed from the fillets. During this whole process, you should be careful not to cut yourself.

6. Heating the Skin

Some types of Isaki nigiri are consumed with the skin still on them. For this, the skin is heated instead of removed, which provides a more unique taste.

Heating the skin makes it easier to eat and provides an exclusive flavor to the nigiri. Various methods are used to heat the skin, such as lightly grilling it or pouring boiling water on it before placing it in cold water.

The grilling method makes the Isaki’s skin black, which contrasts with the white flesh of the fish.

Popular Ways of Eating Isaki Fish

You have a variety of options when it comes to eating Isaki fish. Each one gives you a unique taste to enjoy, providing you with an enchanting experience. Given below are some of the most popular Isaki dishes:

1. Shioyaki

Shioyaki is a relatively popular method of eating Isaki. First, salt is sprinkled on the fish, and then it is grilled. You can enjoy the grilled fish, preferably with a dipping sauce.

This dish has a unique taste that will make you want more.  

2. Isaki Sushi

Another popular method of eating Isaki is in the form of sushi. The pinkish color of the fish makes the dish look very appealing. Also, the high amount of fat combined with the amazing taste of sushi rice makes this dish incredibly delicious. 

Isaki nigiri is extremely popular amongst sushi lovers. The high-fat content only makes the nigiri so much better. You can easily find it at most Japanese restaurants. 

3. Isaki Sashimi

Isaki sashimi is another popular item on the menus of Japanese restaurants. The dish consists of thinly sliced pieces of raw Isaki fish. These pieces are eaten with a dipping sauce. Grated ginger and wasabi paste are also served alongside the fish.

This dish really brings out the delicate taste of Isaki fish as the sweet flavor of the fat makes it much more delicious.  

What does Isaki Fish Tastes Like?

Isaki fish has a very delicate and mild taste. It has a distinct sweetness, and its fresh fragrance increases one’s appetite. Furthermore, the texture of the fish is quite firm, and the fat melts in your mouth, allowing you to savor the taste. The process of aging the fish drastically improves these attributes, making it even more delicious.


Japanese grunt or Isaki is a dream come true for fish lovers. It is a delicacy that sushi and sashimi enthusiasts can enjoy. The complicated process of preparing Isaki fish brings out its natural flavor and texture even more.

This popular fish is perfect for you to enjoy the next time you visit a Japanese restaurant.