One of the problems facing the aquaculture industry is the problem of leftover food. It is possible to reduce leftover food by optimizing the feeding timing and the feeding amount. In order to optimize feeding, it is necessary to collect data on the environment inside the cage and the behavior of fish at the feeding timing. In this research, we newly developed an underwater sensing platform that acquires these data in real time. This platform has a three-layer structure using a universal board and is divided into an Arduino layer, a sensor attachment layer, and a sensor connector layer. As a result, we have realized a compact and replaceable platform.