Effects of Pond Water Depth and Method of Aeration on Phytoplankton Communities in Macrobrachium rosenbergii Farming Ponds

Recently, profitable Macrobrachium rosenbergii farming has developed rapidly in Asia. The occurrence of cyanobacterial blooms is one of the major environmental problems usually encountered in freshwater prawn farms. This study investigated the effects of pond water depth and aeration mode on phytoplankton communities in selected M. rosenbergii farming ponds in China. We adjusted pond water depth and aeration mode (pond water depth: 1.2 m or 1.8 m; method of aeration: surface or both surface and bottom) to compare and analyze phytoplankton community structure and characteristics between ecological (pond water depth: 1.8 m, both surface and bottom aeration) and traditional (pond water depth: 1.2 m, surface aeration) farming ponds. Water quality parameters were compared in six aquaculture systems, which were measured in situ or lab. The results showed that ecological culture suppressed Cyanophyta abundance and significantly increased the numbers of phytoplankton species leading to a 30.43–136.84% increase in the number of species for ecological ponds compared with that in traditional ponds. In all seasons, ecological culture tended to have decreased total nitrogen and ammonia nitrogen, and significantly lower total phosphorus and reactive phosphate compared with traditional ponds. In conclusion, ponds should maintain deeper water depth (1.8 m) and higher N/P ratio (>3) to promote phytoplankton diversity and suppress blooms; applying optimized culture may resolve planktonic algae problems in aquaculture ponds in Asia.