|Kanji in this term|
|ころ > ごろ
|ふな > ぶな
Variously spelled in kanji as 煮頃鮒 or 似五郎鮒. The 煮頃 spelling for nigoro is likely ateji. Meanwhile, the 似五郎鮒 spelling points to the likely derivation: this spelling parses out to "resembling (gen)gorō-buna", and as the nigorobuna grows to sizes of 30cm or longer, it begins to resemble the 源五郎鮒 (ゲンゴロウブナ, gengorōbuna), a closely related species also endemic to the lake.
- nigorobuna (Carassius auratus grandoculis), a type of 鮒 (funa, “crucian carp”), an edible freshwater ray-finned fish related to carp and goldfish, endemic to Lake Biwa in Japan
1981, Hitomi, d. 1701, Hitsudai, Hatsuko Yoshii & Shimada Isao, editor, 本朝食鑑 (Honchō Shokkan) (in Japanese), Heibonsha, pages 267: