Effects of Nile Tilapia on Plankton in Enclosures With Different Treatments in Saline-Alkaline Ponds

The effects of Nile tilapia (Orecohromis niloticus) on the plankton communities were estimated in the enclosures with different treatments in salinealkaline ponds.After tilapia were stocked in the enclosures,abundance,the concentration of chlorophyll-a and primary productivity of phytoplankton increased.The biomasses of phytoplankton were composed mainly by smaller species,in which dominant species were small diatom and green algae,and sub-dominant species was Euglenophyta.The biomasses of zooplankton increased too,predominant by copepods,the size of cladocerans tended to small,the density of protozoa increased.Fertilization,especially apply organic fertilizer,could significantly increase the biomass of phytoplankton and decrease transparency depth,but the impacts of apply inorganic fertilizer to primary production and biomass of zooplankton were insignificant.The density and diversity index of plankton and the biomass of zooplankton in enclosure with apply organic fertilizer were higher than those of enclosures with fish,and the growth of tilapia was the fastest in experimental enclosures.The impacts of tilapia filter feeding and apply fertilizer to the community structures of plankton were discussed,and comparison of these results to that of silver carp were carried out.