Freshwater zooplankton in the previous domestic studies includes protozoa, rotifer, cladoceran and copepod. There are numerous species and difficulty in identification for protozoa compared to another three groups, and different emphases are made in ecosystem studies between them. Based on the tendency of the foreign researches, it is suggested that protozoa study is necessarily separated from rotifer, cladoceran and copepod, namely the studied groups on zooplankton comprise rotifer, cladoceran and copepod, exclusive of protozoa.