Abstract: In order to study the plankton community composition and its annual dynamic change characteristics in the rice-crayfish field, monthly plankton samples were collected, and the structure, diversity, species and quantity of plankton community were detected and analyzed. The results showed that：①In the ditches, there were 125 species of phytoplankton in 7 phyla, significantly higher than that in field surface, and 57 species of zooplankton in 4 species were determined, which had no significant difference from the field surface; The species number of chlorophyta and protozoa were absolute dominant. ②The annual average values of diversity index, richness index and evenness index of phytoplankton in ditches which for crayfish lived were 1.944, 2.481 and 0.540, respectively; there was no significant difference in diversity index between the two fields. The diversity index, richness index and evenness index of zooplankton in ditches were 1.726, 1.865 and 0.654, respectively. The diversity index was the lowest in April and the highest in August. ③Oocystis sotilaria was dominant species from October to march and April of the following year, Tribonema vulgare Pasch was dominant species from May to September, and Scenedesmus quadricauda was dominant species from June to October. The dominant species were copepodite in December and February. The nauplii in March and April were the dominant species in the field surface, and in ditches,Tintinnopsis was dominant species in April, the dominant species were all Pelomyxa palustris Greeff. from May to August, and Moina affinis Birge. was all dominant species from September to November. ④The annual average density of phytoplankton was 1 403 858 ind/L, the annual average biomass was 0.155 37 mg/L, the density in March was the highest and in February was the minimum, the biomass in May was the highest and in October was the minimums, and the density and biomass of phytoplankton in the ditches were higher than those in the field surface. The annual density and biomass of zooplankton were 4 248 ind/L and 9.28 mg/L respectively in the field surface, the density was the highest in April and minimum in February, the biomass was the highest in December and minimum in February. The density and biomass of zooplankton in the field were higher than that in the ditch.

Key words: Procambarus clarkii, rice and shrimp farming, plankton, community