This study was conducted to assess the physicochemical characteristics of Bigaan River and determine species richness and distribution of Ichthyofauna. Water samples were collected from three sampling sites of Brgy. Gango, Brgy. Indahag and Brgy. Cugman using grab sampling method during the wet season to determine water quality parameters namely: Total Solids, Total Suspended Solids (TSS), Turbidity, Total Dissolved Solids (TDS), Conductivity, Density, Redox Potential (ORP), pH, Salinity, Biochemical Oxygen Demand (BOD), Nitrates, Potassium, Phosphate, and Mercury while other parameters were measured onsite namely: Temperature, Dissolved Oxygen (DO), and Flowrate. The collection of fish species was done using purposive sampling. The findings of the study revealed that all physicochemical parameters have not exceeded the given standard values of DAO 2016-08. Results also showed significant differences in the parameters: total dissolved solids and turbidity. There were five identified Ichthyofauna species present in Bigaan River and it showed low diversity. Puntius binotatus is the most abundant species and Oreochromis niloticus is the least number of Ichthyofauna species. The Ichthyofauna species richness and distribution identified in Bigaan River have different tolerance on water quality. Some species were tolerant and sensitive to the water quality fluctuations and they were absent in a particular area. Although Bigaan River is within the acceptable level for Class C waters according to DAO-2016-08; however, water quality in Bigaan River limits the condition of Ichthyofauna species survival and growth because it was disrupted by sudden changes in the water quality.
