This study was undertaken to examine the effect of probiotic product on phytoplankton community in 6 intensive white shrimp Litopenaeus vannamei culture ponds. Three ponds were applied probiotic product, 3 ponds without probiotic application served as control group. Probiotic product was applied weekly and water samples were collected 10 day per times. The results showed that there were 131 species were found including 54 of diatoms, 32 of green algae, 26 of euglenoid, blue-green algae and dinoflagellate being lowest (8-11 species). The freshwater origin species highly increased at the end of the crop. The major genus adapting to low salinity and eutrophic evironment were Euglena, Chlamydomonas, Scenedesmus, Phormidinium, Microcystis, Navicula, and Nitzschia. The results also indicated that the diversity of phytoplankton was low and showed the declined trend at the end of the crop. The ponds with probiotic application had better water quality and maintained phytoplankton community compared to those of control group.
Key words: Probiotic product, phytoplankton, white shirmp.