The iwame trout or markless trout is a variety of salmonid fish inhabiting some fresh waters of

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. It is an intra-specific mutant

morph Morph may refer to: Biology * Morph (zoology), a visual or behavioral difference between organisms of distinct populations in a species * Muller's morphs, a classification scheme for genetic mutations * "-morph", a suffix commonly used in tax ...

of the

masu salmon The masu salmon (''Oncorhynchus masou''), also known as masu ( ja, マス, , trout) or in Japan, is a species of salmon belonging to the genus '' Oncorhynchus'', found in the North Pacific along Northeast/East Asian coasts from the Russian Far ...

(''Oncorhynchus masou'') 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

recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

ly inherited. This morph occurs in the ''amago'' subspecies (''

Oncorhynchus masou ishikawae The amago or the red-spotted masu salmon (''Oncorhynchus masou macrostomus'') is a salmonid fish endemic to western Japan, and a subspecies of the more widespread Northwest Pacific masu salmon or cherry salmon (''Oncorhynchus masou''). It i ...

'') in Western Japan, and apparently also in the

nominate subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

''yamame'' (''Oncorhynchus masou masou''), if these are not identical. The morph was scientifically described as a distinct species ''Oncorhynchus iwame'' in 1961 by

Kimura Kimura (written: lit. "tree village") is the 17th most common Japanese surname. Notable people with the surname include: *, Japanese novelist *, Japanese footballer *, Japanese botanist *, Japanese idol and singer *, Japanese footballer *, Japanes ...

& 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.

References

* Kano, Y., Shimizu, Y., Kondou, K. 2006. Sympatric, simultaneous, and random mating between markless trout (iwame; ''Oncorhynchus iwame'') and red-spotted masu salmon (amago; ''Oncorhynchus masou ishikawae''). Zoological Science 23:71-77. * Kano, Y., Kondou, K., Shimizu, Y. 2009. Present status and conservation of the markless forms of stream-resident masu salmon ''Oncorhynchus masou'' (the so-called 'iwame') in Japanese mountain streams. Ichthyological Research 57:78-84 * Oncorhynchus Freshwater fish of Japan Taxonomy articles created by Polbot {{Salmoniformes-stub