The Biwa trout (''Oncorhynchus rhodurus'') is an

anadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

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 of the genus ''

Oncorhynchus ''Oncorhynchus'', from Ancient Greek ὄγκος (''ónkos''), meaning "bend", and ῥύγχος (''rhúnkhos''), meaning "snout", is a genus of ray-finned fish in the subfamily Salmoninae of the family (biology), family Salmonidae, native to col ...

'',

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Lake Biwa is the largest freshwater lake in Japan. It is located entirely within Shiga Prefecture (west-central Honshu), northeast of the former capital city of Kyoto. Lake Biwa is an ancient lake, over 4 million years old. It is estimated to be the 13 ...

Shiga Prefecture is a landlocked prefecture of Japan in the Kansai region of Honshu. Shiga Prefecture has a population of 1,398,972 as of 1 February 2025 and has a geographic area of . Shiga Prefecture borders Fukui Prefecture to the north, Gifu Prefecture to th ...

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 ...

, but also introduced to

Lake Ashi , also referred to as Hakone Lake or Ashinoko Lake, is a scenic lake in the Hakone area of Kanagawa Prefecture in Honshū, Japan. It is a crater lake that lies along the southwest wall of the caldera of Mount Hakone, a complex volcano that last ...

and

Lake Chūzenji , also called Sea of Happiness, is a scenic lake in Nikkō National Park in the city of Nikkō, Tochigi Prefecture, Japan. It was created 20,000 years ago when Mount Nantai (2484 m) erupted and blocked the river. The lake has a surface ar ...

. While called

trout Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...

, the fish is most closely related to the masu salmon (''Oncorhynchus masou'') of the western

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

, and is most often considered a subspecies of it, ''Oncorhynchus masou rhodurus''. ''rhodurus, Oncorhynchus''
In: W. Eschmeyer:

Catalog of Fishes Catalog of Fishes is a comprehensive on-line database and reference work on the scientific names of fish species and genera. It is global in its scope and is hosted by the California Academy of Sciences. It has been compiled and is continuously up ...

Online Database. California Academy of Sciences. Downloaded 16 Feb 2015 Biwa trout is found only in the waters of northern Lake Biwa, and feeds on

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

, freshwater

prawn Prawn is a common name for small aquatic crustaceans with an exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the intern ...

aquatic insects Aquatic insects or water insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some ''diving'' insects, such as predatory diving beetles, can hunt for food underwater where land-living insects c ...

worm Worms are many different distantly related bilateria, bilateral animals that typically have a long cylindrical tube-like body, no limb (anatomy), limbs, and usually no eyes. Worms vary in size from microscopic to over in length for marine ...

s, '' ayu'' and other small fishes, and sometimes small mammals. Adult Biwa trout usually range from in length and in weight, although large specimens can be up to long and in weight.

Use as food

Biwa trout represents a unique

food fish Many species of fish are caught by humans and consumed as food in virtually all regions around the world. Their meat has been an important dietary source of protein and other nutrients in the human diet. The English language does not have a s ...

for the Shiga Prefecture. Biwa trout and its

caviar Caviar or caviare is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or spread. Traditionally, the term caviar refers only to roe from wild sturgeon in the Caspi ...

are considered a delicacy. Usual ways to prepare the trout is as

sashimi is a Japanese cuisine, Japanese delicacy consisting of fresh raw fish or Raw meat, meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means 'pierced body', i.e., "wikt:刺身, 刺身" = ''sashimi'', whe ...

, by

grilling Grilling is a form of cooking that involves heat applied to the surface of food, commonly from above, below or from the side. Grilling usually involves a significant amount of direct, radiant heat, and tends to be used for cooking meat and v ...

with salt, in meuniere, or by

smoking Smoking is a practice in which a substance is combusted, and the resulting smoke is typically inhaled to be tasted and absorbed into the bloodstream of a person. Most commonly, the substance used is the dried leaves of the tobacco plant, whi ...

deep-frying Deep frying (also referred to as deep fat frying) is a cooking method in which food is submerged in hot fat, traditionally lard but today most commonly oil, as opposed to the shallow frying used in conventional frying done in a frying pan. Norm ...

simmering Simmering is a food preparation technique by which foods are cooked in hot liquids kept just below the boiling point of water (lower than ) and above poaching temperature (higher than ). To create a steady simmer, a liquid is brought to a boil, ...

, ''etc''. The fish has a reputation as being very difficult to catch by

angling Angling (from Old English ''angol'', meaning "hook") is a fishing technique that uses a fish hook attached to a fishing line to tether individual fish in the mouth. The fishing line is usually manipulated with a fishing rod, although rodless te ...

. File:Grilling with salt-rhodurus.jpg, Grilled File:20240714 biwamasubutteryakiju.jpg, Grilled with rice File:20240714 biwamasutirasizusihuju.jpg, Raw '' chirashizushi'' with rice File:Rhodurusっ子（魚卵）のしょうゆ漬.JPG, Roe pickled in

soy sauce Soy sauce (sometimes called soya sauce in British English) is a liquid condiment of China, Chinese origin, traditionally made from a fermentation (food), fermented paste of soybeans, roasted cereal, grain, brine, and ''Aspergillus oryzae'' or ''A ...

References

External links

*Yoshikazu Fujiok
Profile of Biwamasu
Trout and Seasons of The Mountain Village. www.hi-ho.ne.jp

* ttps://web.archive.org/web/20061201045002/http://members.aol.com/user231961/biwa.htm Fishing info. of Biwa trout (Japanese - at Archive.org) Oncorhynchus Endemic fish of Japan Freshwater fish of Japan Fish described in 1925 Taxa named by David Starr Jordan {{Salmoniformes-stub