The impact of net-isolated polyculture of tilapia (Oreochromis niloticus) on plankton community in saline-alkaline pond of shrimp (Penaeus vannamei)

We used 12 land-based experimental enclosures (6 m 9 5 m) in a saline-alkaline pond of shrimp (Penaeus vannamei) to determine the impact of net-isolated polyculture of tilapia (Oreochromis niloticus) on plankton communities for 40 days. Tilapias were stocked in net cages suspended in enclosures, in polyculture ponds including tilapia and shrimp. Four tilapia biomass were tested: 0, 39, 115 and 227 g m(-2). Shrimp stocking biomass were 0.7 g m(-2) in all treatments. There were three replicates in each treatment. Our results showed that the presence of tilapia significantly reduced phytoplankton biomass directly through predation and indirectly through top-down effect. The stocking of tilapia reduced zooplankton biomass, particularly rotifer biomass. However, copepod biomass was not been significantly affected. So, net-isolated polyculture of tilapia can thus have a strong impact on phytoplankton allowing the coexistence of large numbers of copepods with planktivorous fish and improving the water quality of shrimp ponds.