Dynamics of cyanobacteria planktothrix species (Oscillatoriales: Phormidiaceae) in Earthen fish ponds, Northwestern Bangladesh

The seasonal abundance, dynamics and composition of the filamentous Cyanobacteria Planktothrix spp. was studied over a 1-year period in two storm-water-fed earthen fishponds in Rajshahi city, northwestern Bangladesh. Sampling was conducted monthly using plankton net (25 μm mesh size) and the samples preserved in 5% formalin. Water quality parameters including water temperature, transparency, pH, dissolved oxygen (DO), biological oxygen demand (BOD), free carbon dioxide (CO2), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N), ammonium (NH4 +), oxidation reduction index (rH2) were recorded during each sampling. Two species; Planktothrix agardhii and Planktothrix rubescens were identified during the study with P. agardhii recording higher abundance (p