Oncorhynchus masou, known as the masu salmon or the cherry salmon, is a species of salmon found in the Western Pacific Ocean along East Asia, ranging from the Kamchatka, Kuril Islands, Sakhalin, Primorsky Krai south through Korea, Taiwan and Japan). There are a number of subspecies, including Oncorhynchus masou masou (e.g. in Korea), the critically endangered, landlocked Taiwanese or Formosan salmon Oncorhynchus masou formosanus found in certain freshwater systems of Taiwan, and the masu salmon Oncorhynchus masou macrostomus in Japan. All three subspecies are sometimes collectively referred to as the masu salmon.
On average, this salmon prefers a temperate climate, around the area of 65° N - 58° N, and in the sea, it prefers a depth range of 0 – 200 m.
A masu salmon which has reached sexual maturity has a darkened back, and the stripes on the body sides become bright red with crimson tinge to merge on the abdomen into one common longitudinal band of lighter color. It is for this reason that it was given the name Cherry Salmon.
As adults, masu salmon tend to weigh 2 to 2.5 kg and measure roughly 50 cm in length. The maximum size that can be attained by this species (which is in the region of Primorsky Krai) is 71 cm long and 9 kg in weight.
Like other Pacific salmon, its life cycle is subdivided into marine and freshwater periods; in rivers, this species lives from 1 to 3 years and can form living fresh-water forms. The sea life cycle, depending on the age of the young, continues for 2 to 3.5 years. In the sea, the masu salmon feed intensely on crustaceans, less often on young fish. On attaining sexual maturity, in its third to seventh years of life it enters rivers to spawn. Its spawning run starts earlier than that of other salmon species.
After spawning, most passing fish die, and those that remain alive (preferentially dwarf males) participate in spawning next year, too. Emerging from the nest, the young do not roll into the sea but remain in spawning areas, in the upper reaches of rivers, and on shallows with weak currents. The young move to pools and rolls of the river core to feed on chironomid, stone fly and may fly larvae, and on air insects. The masu salmon rolls into the sea in its second, occasionally even third year of life.
This salmon, like most others, is a highly commercial species caught in fisheries, raised for aquaculture, and sought after as a game fish. It is marketed fresh and frozen and is often eaten broiled or baked.
Subspecies and morphs
- Oncorhynchus masou masou - masu salmon
- Oncorhynchus masou rhodurus - Biwa trout
- Oncorhynchus masou macrostomus - amago, red-spotted masu salmon
- Oncorhynchus masou formosanus - Taiwanese land-locked salmon