According to narrow fluctuation of Phetchaburi municipal wastewater quality indicators, the sampling period for collecting phytoplankton and zooplankton in oxidation ponds 2, 3, 4, and 5, (except oxidation pond 1 namely sedimentation pond) was taken place on 10 times during October 2014 to July 2015 as shown in Table 1 Theoretically, the growth rate of plankton (phytoplankton and zooplankton) is equivalent to increment weight of herbivore fishes as aqua-culturing in oxidation ponds which is supposed to be aquatic ecosystems composing of solid and dissolved organic matters, plant nutrients, toxic chemicals, oxygen, carbon dioxide and other gases, microorganisms as the factors involving in phytoplankton, zooplankton, and herbivore fishes. Naturally, life cycle of planktons is aged approximately 1-2 weeks and blooming at the period of high intensity of sunlight, especially wavelength of visible light (0.38-0.78 micron) in early winter season. However, the average monthly amount of growing stock of phytoplankton and zooplankton were presented in Table 1 and Figure 3 which indicated in seasonal changes rather than narrow changes of treated wastewater concentration