This book was written on the basis of research themes on community dynamics of the population structure of zooplankton, suspended and attached algae in high altitude eastern Himalayan region of India. The study site is located in high altitude wet rice fields of Eastern Himalayan region of Arunachal Pradesh, India with an altitude about 1800 ft. above mean sea level. The high altitude wet rice cultivation of this region is well known for their unique system of fish integration. The settled agriculture in this mountain valley rice fields is gaining a national importance as the model of "Sustainable Land Use". They are habituated in raising fish concurrently as companion crop of rice as their main food source in high rainfall mountainous zone since last 1960 years. The results indicated that the diverse population of zooplankton showed significant monthly variations. The diversity and dynamics of zooplankton being the naturally available fish food organisms towards the development of rice field fishery. The frequently changing nature of rice fields according to the different growth stages of rice provide congenial habitat for rich number of diversified organisms.