源五郎鮒

Compound of 源五郎 (Gengorō, “Japanese diving beetle, Cybister chinensis”, also a male given name) +‎ 鮒 (funa, “crucian carp”).[1][2] The funa changes to buna as an instance of rendaku (連濁).

The derivation is somewhat muddled.

• According to one theory, the Gengorō portion was the name of a fisherman who fished in Lake Biwa, and every morning, presented the best of his catch of funa to the local lord.[1]
• In another theory, this term arose from a tale about a Lake Biwa fisherman named Gengorō, who fell in love with a noblewoman and arranged a secret meeting with her by hiding a note inside a gengorōbuna fish that he had caught and presented to her.
• The first portion is also the word for the Japanese diving beetle, possibly because the fish eats insects as part of its diet, or because of a superficial similarity in shape.

• (Tokyo) げんごろーぶ​な [gèńgóróóbúꜜnà] (Nakadaka – [6])[2][3]
• IPA^(key): [ɡẽ̞ŋɡo̞ɾo̞ːbɯ̟ᵝna̠]

源(げん)五(ご)郎(ろう)鮒(ぶな) or 源五郎鮒(ゲンゴロウブナ) • (gengorōbuna) ^{←げんごらうぶな (gengoraubuna)?}

1. Carassius cuvieri the Japanese crucian carp or white crucian carp, a type of 鮒 (funa, “crucian carp”), an edible freshwater ray-finned fish related to carp and goldfish and endemic to Lake Biwa in Japan

As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts (where katakana is customary), as ゲンゴロウブナ.

• Gengorōbuna entry at Nihon Jiten (in Japanese)