Iwame trout
The iwame trout or markless trout is a variety of salmonid fish inhabiting some fresh waters of Japan. It is an intra-specific mutant morph of the masu salmon that is characterized by a lack of the lateral spot marks typical of the young fish in most populations. The iwame is a stream-resident morph that does not migrate to the sea. It occurs together with the standard phenotype in some populations. This morph is recessively inherited.
This morph occurs in the amago subspecies in Western Japan, and apparently also in the nominate subspecies yamame, if these are not identical.
The morph was scientifically described as a distinct species Oncorhynchus iwame in 1961 by Kimura & Nakamura. In the 2000s, the iwame morph was shown to occur as a polymorphism in random mating populations of O. masou, and is no more thought to have taxonomical value.
