Oncorhynchus masou, commonly known as the Masu salmon, is a species of salmon found primarily in the western Pacific Ocean. It inhabits coastal waters and rivers of Japan, Korea, and Russia. This fish is known for its distinctive coloration, which varies from greenish-blue to silver, and it can grow up to 75 centimeters in length. Masu salmon are anadromous, meaning they migrate from the ocean to freshwater rivers to spawn. They typically spawn in the fall, and their eggs hatch in the spring. This species plays a significant role in the ecosystem and is also important for local fisheries and cultural practices in the regions where it is found.