Biwa trout nigiri

Biwa trout (Biwamasu)

【Nigiri sushi: Shiromi】
The Biwa trout is a species endemic to Lake Biwa, but following reintroduction efforts, it is also found in Lake Kizaki (Nagano Prefecture), Lake Chuzenji (Tochigi Prefecture), and Lake Ashi (Kanagawa Prefecture). As indicated by its scientific name, Oncorhynchus masou subsp., it is considered a subspecies of the masu salmon.

It reaches a maximum length of about 60 cm and has pale orange spots on its sides, which gradually fade as it grows. Adult Biwa trout have a silvery body.

Furthermore, Biwa trout have long been farmed in Japan. In fact, near Lake Biwa in Shiga Prefecture, there is a well-known Biwa trout hatchery that has been in operation since 1878.

It is interesting to note that, although the Biwa trout is originally derived from a Pacific anadromous species, it also exhibits anadromous-like behavior in a lake environment. It migrates between Lake Biwa, a freshwater body, and the surrounding rivers depending on the water temperature.

The wild Biwa trout season runs from June through early September. During this time, its flesh is rich but not overly fatty. Furthermore, when you put it in your mouth, the umami flavor of the fat spreads gently across the palate, as if it were melting on the tongue. It is also a sushi ingredient that allows you to fully appreciate the trout's characteristic aroma.

On June 21, 2025, an international academic journal published a new scientific name, “Oncorhynchus biwaensis,” for Biwa trout (salmon) species, which is endemic to Lake Biwa.

【Related contents】
List of White flesh fish (Shiromi)

(Revision date: August 25, 2026)