Abstract

The Riam Kanan reservoir is a freshwater reservoir that the public has long used, one of which is for fish farming. The aim of this study was to determine the presence and abundance of phytoplankton as natural feed for betutu larvae fish and an indicator of the environmental productivity of the Riam Kanan reservoir. The research was carried out in the Riam Kanan reservoir for 5 months (July-November 2020). Sampling was carried out at five different stations. Each sampling was taken about 20 liters of reservoir water. Furthermore, chemical measurements of reservoir water include dissolved oxygen (DO), carbon dioxide (CO2), pH, NH3, and physical measurements include temperature, brightness, and turbidity. Reservoir water also measured the abundance, diversity, evenness, and dominance of phytoplankton. The results showed that the average water quality values of the Riam Kanan reservoir during July-November 2020 were a value of 28.7oC for temperature, the brightness of 1.8m, turbidity of 9.1 NTU, DO of 4.5 mg/L, CO2 of 10.9 mg/L, pH of 8.2, and NH3 of 0.3 mg/L. The phytoplankton found were phylum Chlorophyta (48%), Cynophyta (31%), Bacillariophyta (18%), and Euglenophyta (3%). The existence of phytoplankton was also very varied; in July, only 3 phyla existed, but from August to November, 4 phyla existed. Measurement of the diversity index showed that the phytoplankton in the Riam Kanan reservoir was in the medium category with high evenness and no species dominance. These findings indicate that the Riam Kanan reservoir is still provides a natural feed source for betutu fish larvae.