Hyonenzu were originally painted with a zen mondo (Zen riddle) on how to hold down a slippery catfish with a slick gourd and a picture in which a monkey is trying to hold down a catfish with a gourd was comically painted in Otsu-e.
つるつるの瓢箪でぬめるナマズを押さえつけるにはどうするかという禅問答をモチーフとしたのが本来の瓢鮎図で、大津絵では猿が瓢箪で鯰を押さえようとする図が滑稽に描かれる。