[4] The fish is dark olive with black spots on its back, and grows to approximately one foot (30 centimetres) in length.

[2] In 1940, water was introduced into Lake Tazawa from Tama River to increase hydroelectric power generation from the local dam.

[2] The introduced water was strongly acidic and killed the entire population of Kunimasu,[2] as salmon are highly sensitive to changes in pH.

[2] But in 2010, nine specimens of the fish were discovered by a group of scientists in Lake Saiko, which are assumed to be descendants of the original eyed eggs introduced in the 1930s.

[2] Kunimasu is very closely related to another species of land-locked sockeye salmon Oncorhynchus nerka, commonly called kokanee or Himemasu.

[2] This is supported by their number of gill rakers[2] and the observed habitat preference of the species to occupy cold, deep lake water.

[6] During spawning, the bodies of male and female Kunimasu undergo morphological changes that differ among fish according to their size and range, but generally consist of the appearance of a humpback and concave snout.