Based on the photosynthesis of microalgae mainly, it was clarified that bacteria, protozoa and other microorganisms form microbial food assemblages using the organic matter produced by the algae and that these assemblages play a significant role in the aquatic food chain. Based on this concept, larvae of the prawn, Penaeus monodon and of the crab, Portunus trituberculatus were reared. The growth of the larvae and their production were markedly promoted by the introduction of certain bacterial strains such as PM-4 and NS-110. When the ciliated protozoon, Strombidium sulcatum, isolated in a prawn culture pond was used as feed for the larvae of Penaeus monodon, the growth of the larvae was also promoted.