草鱼（学名Ctenopharyn odon idellus），又称鲩鱼（汉语拼音：huàn yú）、混子、草青等，为辐鳍鱼纲鲤形目鲤科的其中一种。

本鱼体侧扁且延长，吻短而圆钝，口大，无须，特征是具2排梳状咽头齿。鱼体背部青褐色而略带黄色，腹部乳白，鳞片大且具黑缘；胸鳍与腹鳍略带黄色，尾鳍浅叉形，背鳍硬棘3枚； 背鳍软条7至8枚；臀鳍硬棘3枚；臀鳍软条7至11枚，体长可达1.5公尺。

The grass carp (Ctenopharyngodon idella) is a herbivorous, freshwater fish species of the family Cyprinidae, and the only species of the genus Ctenopharyngodon. It is a large cyprinid native to eastern Asia, with a native range from northern Vietnam to the Amur River on the Siberia-China border.