Effects of Macrobrachium nipponense on Phytoplankton Communities and Water Environmental Factors in Macrobrachium rosenbergii Culture

Excessive feed input led to eutrophication and Cyanobacterial blooms in the culture of giant freshwater prawn (GFP, Macrobrachium rosenbergii). In order to improve the water quality and control the Cyanobacterial blooms, we tried the mixed culture of oriental river prawn (ORP, Macrobrachium nipponense), which can feed on plant and organic debris. In this study, the culture trial began on June 20th and ended on September 10th. The control group (CG) was GFPs monoculture, while the experimental group (EG) cultured GFPs and ORPs. Water samples were collected from the ponds for five times to compare the changes of water environmental factors and phytoplankton communities in CG and EG. Phosphate, nitrite, sulfide, and ammonia nitrogen in CG were significantly higher than those in EG at the end of culture (p < 0.05). In the middle stage of culture, the Margalef index, Pielou index, and Shannon–Wiener index of EG were significantly higher than those of CG (p < 0.05). The biomass and density of phytoplankton in EG were lower than those in CG, and the occurrence of Cyanobacterial blooms in EG was later. The results indicated that ORPs in the mixed culture model effectively transformed and stored part of the energy by consuming the residual bait, which reduced the degree of eutrophication and Cyanobacterial blooms.