One of freshwater rotifer (Brachionus calyciflorus) is very useful as a live food organism for early larval rearing of freshwater aquaculture industry. However, the knowledge about freshwater rotifer culture is scarce. On the other hand, marine rotifer culture as live food organisms is done, almost perfectly. In this study, I show to be benefit experimental results for successful freshwater larval rearing through the observation with microcosm structure in freshwater rotifer culture tanks.