The iwame trout (, , 'rock lady fish') or markless trout is a variety of

salmonid Salmonidae (, ) is a family of ray-finned fish, the only extant member of the suborder Salmonoidei, consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmon (both Atlantic a ...

fish inhabiting some

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

systems of

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. It is an intra-specific mutant morph of the masu salmon (''Oncorhynchus masou'') that is characterized by a lack of the lateral camouflage spots (parr marks) typical of

juvenile salmon Fish go through various biological life cycle, life stages between fertilization and adulthood. The life of fish start as spawn (biology), spawned fish egg, eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of ...

in most populations. The ''iwame'' is a

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

-resident morph that does not migrate to the sea as adults. 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 ...

ly inherited and occurs together with the standard

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

in some populations. This morph occurs in the landlocked ''amago'' subspecies ('' Oncorhynchus masou ishikawae'') in western Japan, and apparently also in the

nominate subspecies In biological classification, subspecies (: 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. ...

''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: or lit. "tree village") is the 17th most common Japanese surname. Notable people with the surname *, Japanese novelist *, Japanese footballer *, Japanese botanist *, Japanese idol and singer *, Japanese footballer *, Japanese s ...

& 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