Effects of different cultural patterns of Macrobrachium rosenbergii on plankton

The plankton in water under six cultural patterns of Macrobrachium rosenbergii was evaluated in an enclosure experiment. The cultural patterns included prawn monoculture group (MP), prawn with aquatic plant (Lemna minor, water-coverage 5%) group (PP), prawn with silver carp (Hypophthalmichthys molitrix) group (PF), prawn with mussel (Anodonta woodiana) and H. molitrix group (PMF), prawn with mussel and aquatic plant group (PMP), prawn withA. woodiana, L. minor and H. molitrix group (PMPF). Four replicates of each treatment were set up in this study. After 64 days of culturing, the phytoplankton and zooplankton (Rotifera, Cladocera and Copepods) in water of each cultural pattern were evaluated. The results showed that there were four common phytoplankton dominant species in all cultural patterns. However, the most dominant phytoplankton species was different. The most phytoplankton dominant species were Dinobryon in MP group, and Oscillatoria minima in culturing L. minor groups (PP and PMP), and Synedra sp. in H. molitrix polyculture groups (PF, PMF and PMPF). There were no common dominant species of zooplankton in six cultural patterns. The density of phytoplankton in the PF group was the highest, and it was higher than that of MP, PP and PMP by 78%, 53% and 61%, respectively. In contrast, the density of zooplankton was the highest in MP, and that of PF group was the lowest. The density of zooplankton in H. molitrix polyculture groups (PF, PMF and PMPF) was significantly lower than that of other three groups. The results showed that the stocking H. molitrix in M. rosenbergii pond can increase the density of phytoplankton and reduce the density of zooplankton. Both L. minor and H. molitrix could affect dominant species in pond.