The Biwa trout (Oncorhynchus rhodurus) is an anadromous salmonid fish of the genus Oncorhynchus, endemic to Lake Biwa in Shiga Prefecture, Japan, but also introduced to Lake Ashi and Lake Chūzenji. While called trout, the fish is most closely related to the masu salmon (Oncorhynchus masou) of the western Pacific Ocean, and is most often considered a subspecies of it, Oncorhynchus masou rhodurus. Biwa trout is found only in the waters of northern Lake Biwa, and feeds on plankton, freshwater prawns, aquatic insects, worms, ayu and other small fishes, and sometimes small mammals. Adult Biwa trout usually range from 40 to 50 cm in length and 1.5 to 2.5 kg in weight, although large specimens can be up to 70 cm long and 5.0 kg in weight.

Use as food

Biwa trout represents a unique food fish for the Shiga Prefecture. Biwa trout and its caviar are considered a delicacy. Usual ways to prepare the trout is as sashimi, by grilling with salt, in meuniere, or by smoking, deep-frying or simmering, etc. The fish has a reputation as being very difficult to catch by angling.