Abstract: To study an application of low-value fishmeal (i.e. organic manure) and the effect of different nitrogen (N) and phosphorus (P) ratios (N/Ps) to the composition of algae prevailing in fertilized ponds for culturing Artemia. Phytoplankton composition and their abundance were determined through qualitative and quantitative sampling and analyses. The experiment included five treatments, control treatment using chicken manure (300 g/m3), the others with fishmeal in different rates (i.e. 30 g/m3, 60 g/m3, 90 g/m3, 120 g/m3) with 3 replicates each and in a combination with inorganic fertilizer. Result indicated that the algal density of the experiment varied from 318 × 103to 2,590 × 103 cells/mL and a significant difference among treatments (p < 0.05). The density of algae at the second treatment (30 g/m3) is the highest with a mean density of 2,590 × 103cells/mL. There are 38 phytoplankton species belonging to five phyla of algae, i.e. Bacillariophyta, Cyanophyta, Chlorophyta, Dinophyta and Euglenophyta. Also, there are 18 species of Bacillariophyta, 14 species of Chlorophyta, 4 species of Cyanophyta, 1 species of Dinophyta and 1 species of Euglenophyta. Algae compositions were 32, 34, 31, 27 species at control treatment, and 30 g/m3, 60 g/m3, 90 g/m3, 120 g/m3 fishmeal treatments, respectively. The dominant genus was usually Nitzschia, Thalassiosira, Navicula (Bacillariophyta), Tetraselmis (Chlorophyta), Oscillatoria (Cyanophyta), Euglena (Euglenophyta). Euglena usually appeared in the late phase of the experiment.