the most affected Zooplankton taxa were cladocerans (Daphina group galeata) , copepods (cyclopoids and coppepod nauplii) and rotifers (Keratella cochleata) showing in all the cases significant decreases in abundance at 1 microa คลอร์ไพริฟอสต่อลิตร. the calculated NOEC was 0.1 ไมโครกรัมต่อลิตร for these taxa as well as for the community. ชุมชนแพลงก์ตอนสัตว์ was considered to berecovered after 99 วัน post-application. the results of this experiment were similar to those derived from mesocosm/microcosm studies performed in temparate reqions. this indicates that a chlorpyrifos concentration of 0.1 microq chlorpvrifosต่อลิตร could be the indicates safe level for ชุมชนแพลงก์ตอนสัตว์ใน different climatic regions. However at teatment level of 1.0 ไมโครกรัมต่อลิตร the time required for full recovery of the affected populations (particularly cladocerra) was longer than in the other การทดลอง performed in temperate regions