Unknown. Historical sources from the Muromachi period spell this in kanji as 土長, and in historical kana as どぢやう (dodyau). Spellings such as どぜう (dozeu) were apparently later innovations.
Theories suggest that the name may refer to the fish's apparent ability to thrive in muddy conditions. The modern kanji spelling is an example of jukujikun (熟字訓).
泥鰌 (hiragana どじょう, katakana ドジョウ, rōmaji dojō, historical hiragana どぢやう, historical katakana ドヂヤウ)
- Misgurnus anguillicaudatus: the pond loach, weather loach, or weatherfish
As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts, as ドジョウ.