News
SpeciesScientists Discover Mysterious New Fish in the Red Sea – and Have Never Seen It AgainOceanEye to eye with Britain's hidden sharks at SharkAdemy - OceanographicRiversIn October, biologists surveying a New York harbor for invasive fish pulled up a bright yellow one. It wasn't an invasive species at allOceanShedd Aquarium Sends Shark Eggs to Bolster Wild PopulationsSpeciesA rare fish has been found in Lake Ontario, North America, whose entire body is golden. It is a nati..OceanThe Great Sea Reef Is Fiji’s Wildest Dive, and a New Frontier for ConservationOceanEckerd College professor contributes to designating Biscayne Bay an Important Shark and Ray AreaSpeciesRio Verde Grande Survey Identifies Fifty-Three Fish Species Facing Flow ReductionsFisheriesAdams River Salmon Run in Thompson-NicolaIndiaHilsa production dropped 26% in five years, fisheries minister tells parliamentSpeciesScientists Discover Mysterious New Fish in the Red Sea – and Have Never Seen It AgainOceanEye to eye with Britain's hidden sharks at SharkAdemy - OceanographicRiversIn October, biologists surveying a New York harbor for invasive fish pulled up a bright yellow one. It wasn't an invasive species at allOceanShedd Aquarium Sends Shark Eggs to Bolster Wild PopulationsSpeciesA rare fish has been found in Lake Ontario, North America, whose entire body is golden. It is a nati..OceanThe Great Sea Reef Is Fiji’s Wildest Dive, and a New Frontier for ConservationOceanEckerd College professor contributes to designating Biscayne Bay an Important Shark and Ray AreaSpeciesRio Verde Grande Survey Identifies Fifty-Three Fish Species Facing Flow ReductionsFisheriesAdams River Salmon Run in Thompson-NicolaIndiaHilsa production dropped 26% in five years, fisheries minister tells parliament
EveryFish
species: Oncorhynchus masou rhodurus Biwa or Masou trout (or Biwa salmon) which returned to river which flowed into the northern Lake Biwa in Shiga Prefecture , Japan for spawning. A breeding color has appeared. Top- 20.

Biwa trout

Salmonid fish endemic to Lake Biwa in Japan

Photo: No machine-readable author provided. Vineyard assumed (based on copyri, CC BY-SA 3.0, via Wikimedia Commons

The Biwa trout is a salmonid fish native to Lake Biwa in Shiga Prefecture, Japan. Described as a distinct species in 2025, it was previously confused with another form. It serves as a local delicacy and is prized by anglers despite being hard to catch.

Share on WhatsApp

  • Endemic to northern Lake Biwa in Japan
  • Described as a new species in 2025
  • Adults commonly weigh 1.5 to 2.5 kg
  • Considered a delicacy in Shiga Prefecture
  • Diet includes small mammals and fish

What it is

The Biwa trout is a member of the salmon family, specifically the genus Oncorhynchus. It is an anadromous fish, meaning it migrates between fresh and salt water, though it is primarily associated with Lake Biwa. Adults typically measure between 40 and 50 centimetres in length and weigh 1.5 to 2.5 kilograms. Larger individuals can reach 70 centimetres and weigh up to 5 kilograms. This species was formally described as separate from similar trout in 2025.

Where it lives

This fish is endemic to the northern waters of Lake Biwa in Shiga Prefecture, Japan. While its natural home is restricted to this large lake, populations have been introduced to other bodies of water. These include Lake Ashi and Lake Chūzenji. The species was once thought to be the same as the trout found in Lake Ashi, but recent studies confirm it is a distinct entity.

How it lives

The Biwa trout has a varied diet that changes with availability. It feeds on plankton, freshwater prawns, aquatic insects, and worms. It also consumes other fish such as ayu and occasionally small mammals. This broad diet supports its growth to substantial sizes within the lake ecosystem. Its behaviour includes migration, characteristic of its salmonid relatives.

Biwa trout
A drawing made by EveryFish from what this page says. It is a diagram, not a picture of the real fish.

Fish and people

In Shiga Prefecture, the Biwa trout is valued as a unique food source. Both the meat and the caviar are regarded as delicacies. Local preparation methods include serving it raw as sashimi, grilling it with salt, or cooking it meuniere style. Other techniques involve smoking, deep-frying, or simmering. Anglers find the fish challenging to catch, adding to its reputation in sport fishing circles.

ja:ビワマス の幼魚。 ja:滋賀県立琵琶湖博物館 飼育展示個体。
ja:ビワマス の幼魚。 ja:滋賀県立琵琶湖博物館 飼育展示個体。. Photo: Totti, CC BY-SA 4.0, via Wikimedia Commons
Biwa trout
Photo: Unknown author, CC BY-SA 3.0, via Wikimedia Commons
バター焼き重
バター焼き重. Photo: メガムギチャ, CC BY-SA 4.0, via Wikimedia Commons
ビワマスのチラシ寿司風重
ビワマスのチラシ寿司風重. Photo: メガムギチャ, CC BY-SA 4.0, via Wikimedia Commons

Questions people ask about Biwa trout

Where is the Biwa trout found?

It is native to the northern part of Lake Biwa in Shiga Prefecture, Japan. It has also been introduced to Lake Ashi and Lake Chūzenji.

Is the Biwa trout good to eat?

Yes, it is considered a delicacy in its home region. The meat and caviar are prepared in various ways, including sashimi, grilling, and smoking.

How big does the Biwa trout get?

Most adults range from 40 to 50 cm in length. Large specimens can grow up to 70 cm long and weigh 5 kg.

Good reading and sources

Where this page comes from

The facts on this page come from the Wikipedia article "Biwa trout", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.

It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.

Like Biwa trout

All salmon and trout
🇺🇸 United States and 1 moreBrook trout A colorful freshwater char native to eastern North America, known for its spotted pattern and status as a popular game fSalmonid · Rivers and lakes · 1814 🇺🇸 United StatesCutthroat trout A group of Pacific trout native to western North America, known for red throat markings.Salmonid · Rivers and lakes · 1793 🇺🇸 United States and 3 moreSockeye salmon Anadromous Pacific salmon known for red spawning colour and zooplankton diet.Salmonid · Rivers and lakes · 1792 WorldBrown trout A widespread salmonid with river, lake and sea forms.Salmonid · Rivers and lakes · 1758

More from Salmonidae

All of them
🇺🇸 United StatesCalifornia golden trout Native high-elevation trout of the Sierra NevadaSalmonid · Rivers and lakes · 1892 🇺🇸 United StatesWestslope cutthroat trout Native salmonid of the upper Columbia and Missouri river basins.Salmonid · Rivers and lakes · 1856 🇬🇧 United KingdomGwyniad Rare whitefish found only in one Welsh lakeSalmonid · Rivers and lakes · 1848 🇺🇸 United States and 1 moreBull trout A large char native to cold rivers of northwestern North America.Salmonid · Rivers and lakes · 1836

Photo credits on this page

The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.

The weekly digest

Every Monday: the fish of the day, new pages on EveryFish, and the conferences and anniversaries of the week ahead.