Nigorobuna

Its habitat is limited to Lake Biwa, its tributaries and distributaries, and irrigation canals, in the Shiga Prefecture (west-central Honshu), northeast of Kyoto.

One has it that it earned the name ni-gorō-buna (Japanese: 似五郎鮒) meaning "gorō-buna's look-alike", because once it attains sizes of approximately 1.2–1.3 shaku (≈feet), it begins to look confusingly similar to the gengorō-buna (源五郎鮒) (C. cuvieri, the wild form of the Japanese crucian carp) which is a closely related species that is also endemic to the lake.

[8][11] Its shape resembles the nagabuna [ja][a] that populate Lake Suwa;[12] its body depth is short, and breadth is wide.

[13] Larvae and juveniles are found on the surface and medium depths entrenched within reeds[13] around the lake, in other words, inlets rich in aquatic plants.

[13] Adults spawn from April to June, laying eggs on aquatic plants when water levels rise due to the rainy season.

[13] The hatchlings live by the reedy shore, and move offshore as they grow, reaching full size in 2 to 3 years.

[19][20] This species is said to make superior funazushi that is tender down to the bones, in contrast to imitations made by using gengoro-buna (Carassius cuvieri) as a substitute.

[24] The impact of predatory fish may be a secondary aggravating factor, the core cause being man-made changes to the lake's landscape according to some opinion.

[26] The current situation is not well-described as blockage by gates; the farmland consolidation [ja] (hojō- seibi) project was conducted that raised the ground of the rice paddies,[27] and instead of drawing water from canals, these farms switched to pumping water via PVC pipes, depriving the aquatic life of their conduits to enter.