# Biwa trout

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{{Short description|Species of fish}}
{{Speciesbox
| name = Biwa trout
| image = Oncorhynchus masou rhodurus.jpg
| taxon = Oncorhynchus biwaensis
| authority = Fujioka ''et al.'' 2025
}}

The '''Biwa trout''', or '''Biwa salmon''' (''Oncorhynchus biwaensis'')<ref name=":0">{{Cite journal |last=Fujioka |first=Yasuhiro |last2=Kuwahara |first2=Masayuki |last3=Tabata |first3=Ryoichi |last4=Fuke |first4=Yusuke |last5=Nakabo |first5=Tetsuji |date=2025-06-21 |title=The Biwa salmon, a new species of Oncorhynchus (Salmonidae) endemic to Lake Biwa, Japan |url=https://doi.org/10.1007/s10228-025-01032-z |journal=Ichthyological Research |language=en |doi=10.1007/s10228-025-01032-z |issn=1616-3915|url-access=subscription }}</ref> is an [anadromous](/source/anadromous) [salmonid](/source/salmonid) fish of the genus ''[Oncorhynchus](/source/Oncorhynchus)'', [endemic](/source/endemic) to [Lake Biwa](/source/Lake_Biwa) in [Shiga Prefecture](/source/Shiga_Prefecture), [Japan](/source/Japan), but also [introduced](/source/Introduced_species) to [Lake Ashi](/source/Lake_Ashi) and [Lake Chūzenji](/source/Lake_Ch%C5%ABzenji).

This species was previously identified to be same animal as ''Oncorhynchus'' (''masuou'') ''rhodurus'' which is first described from Lake Ashi.<ref>{{Cite journal |last=Jordan |first=David Starr |last2=Jordan |first2=David Starr |last3=Hubbs |first3=Carl L. |last4=McGregor |first4=Ernest Alexander |date=1925-06-27 |title=Record of fishes obtained in Japan by David Starr Jordan in Japan, 1922 |url=https://www.biodiversitylibrary.org/part/234844 |journal=Memoirs of the Carnegie Museum |volume=10 |issue=2 |pages=93––346 |doi=10.5962/p.234844|doi-access=free }}</ref> However, The Biwa trout was found to be a separate species from ''O. rhodurus'' and was described as a new species in 2025.<ref name=":0" /> ''O. rhodurus'' may represent a hybrid specimen instead.<ref>{{Cite web |last=宏 |first=瀬能 |date=2008 |title=境界線上で翻弄される箱根の魚たち |url=https://nh.kanagawa-museum.jp/www/pdf/tobira54_3senou.pdf |website=[Kanagawa Prefectural Museum of Natural History](/source/Kanagawa_Prefectural_Museum_of_Natural_History) |access-date=2025-06-30 |archive-date=2025-06-30 |archive-url=https://web.archive.org/web/20250630135732/https://nh.kanagawa-museum.jp/www/pdf/tobira54_3senou.pdf |url-status=dead }}</ref>

Biwa trout is found only in the waters of northern Lake Biwa, and feeds on [plankton](/source/plankton), freshwater [prawn](/source/prawn)s, [aquatic insects](/source/aquatic_insects), [worm](/source/worm)s, ''[ayu](/source/Ayu_sweetfish)'' and other small fishes, and sometimes small mammals.  Adult Biwa trout usually range from {{cvt|40|to|50|cm}} in length and {{cvt|1.5|to|2.5|kg}} in weight, although large specimens can be up to {{cvt|70|cm}} long and {{cvt|5.0|kg}} in weight.

==Use as food==
Biwa trout represents a unique [food fish](/source/food_fish) for the Shiga Prefecture. Biwa trout and its [caviar](/source/caviar) are considered a delicacy. Usual ways to prepare the trout is as [sashimi](/source/sashimi), by [grilling](/source/grilling) with salt, in meuniere, or by [smoking](/source/smoking_(cooking)), [deep-frying](/source/deep-frying) or [simmering](/source/simmering), ''etc''.  The fish has a reputation as being very difficult to catch by [angling](/source/angling).

<gallery widths="120px" heights="120px" mode="packed">
File:Grilling with salt-rhodurus.jpg|Grilled
File:20240714 biwamasubutteryakiju.jpg|Grilled with rice
File:20240714 biwamasutirasizusihuju.jpg|Raw ''[chirashizushi](/source/chirashizushi)'' with rice
File:Rhodurusっ子（魚卵）のしょうゆ漬.JPG|Roe pickled in [soy sauce](/source/soy_sauce)
</gallery>

==References==
* {{FishBase species alt|4731|taxon=''Oncorhynchus rhodurus''|year=2010}}
{{Reflist}}

==External links==
*Yoshikazu Fujioka [http://www.hi-ho.ne.jp/amago/trout/biwamasu2.html   Profile of Biwamasu] Trout and Seasons of The Mountain Village. www.hi-ho.ne.jp
* [https://web.archive.org/web/20070505050021/http://www.nies.go.jp/biodiversity/invasive/detail/50860.html Biwa trout information from the National Institute for ES of Japan (Japanese)]
* [https://web.archive.org/web/20061201045002/http://members.aol.com/user231961/biwa.htm Fishing info. of Biwa trout (Japanese - at Archive.org)]

{{Taxonbar|from=Q74350}}
{{Authority control}}

Category:Oncorhynchus
Category:Endemic fish of Japan
Category:Freshwater fish of Japan
Category:Fish described in 1925
Category:Taxa named by David Starr Jordan 

{{Salmoniformes-stub}}

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Adapted from the Wikipedia article [Biwa trout](https://en.wikipedia.org/wiki/Biwa_trout) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Biwa_trout?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.