Ostorhinchus doederleini is a species of fish in the cardinalfish family, also known by the common names Doederlein's cardinalfish and fourline cardinalfish. In Japanese it is called osuji-ishimochi. It is native to subtropical regions of the western Pacific Ocean, its distribution extending from Japan to Taiwan and Australia to New Caledonia and the Kermadec Islands. This fish lives in rocky habitat types near the shore, such as ledges. It is nocturnal. During the day it hides in caves and rock crevices. It feeds on invertebrates, especially gammarid amphipods.