Shiromi refers to white-fleshed fish. These fish typically inhabit midwater or deeper zones and contain less colored protein in their muscles, resulting in their pale appearance. Because they are less active than red-fleshed fish, they require less oxygen and thus have a lower concentration of chiai (dark, iron-rich meat). Shiromi tends to be lighter in flavor but firmer in texture due to its higher collagen content.
Collagen is especially abundant in fish that twist their bodies when swimming, such as flounder, followed by those that use the lower half of their bodies, like red seabream and Japanese seabass, and finally in fish that rely mainly on tail movement, such as tuna and bonito.
The fat content in Shiromi is generally low—about 1.2% in flounder and 4.7% in sea bream. Most white fish have a delicate, refined taste. Additionally, they enter rigor mortis slowly and remain firm longer, allowing the characteristic crunch to last. Unlike Akami (red-fleshed fish), Shiromi species are not highly migratory. If you can identify the type of fish just by looking at the cut, you can call yourself a true sushi expert.
Interestingly, despite its pink hue, salmon is classified as Shiromi. Its natural flesh is gray, and the pink color comes from the pigments of shrimp and crab in its diet. Likewise, Buri and Shima aji have a beige tone rather than true white. Technically, these fall under a separate category called Iromono, but since the term is not widely known, they are often grouped with Shiromi for simplicity. Once you understand Shiromi in depth, you're on your way to becoming a true sushi connoisseur.
Most Shiromi used in sushi restaurants is sold live. The fish broker performs Ikejime according to the purchasing chef’s instructions, and the timing is carefully planned to maximize umami when the fish is prepared. This process, combined with transportation costs to markets like Toyosu, contributes to Shiromi’s higher price—often at least 50% more than other fish.
Some people claim Shiromi lacks flavor, especially compared to richer fish. In cuisines like French or Chinese, where sauces and broths dominate the flavor profile, the subtlety of white fish is less appreciated. In such dishes, the fish serves more as an umami component than a focal flavor.
However, in nigiri sushi, the nuanced differences between cod, flounder, flatfish, and sea bass are essential. Skilled sushi chefs pay close attention to the flesh quality, fat content, and aroma—crafting each piece so that these subtleties are highlighted and enjoyed.