Includes bibliographical references and appendices.

This preliminary study explores the relationship between physicochemical parameters and freshwater fish occurrence within the Bayawan City Nature Reserve, Negros Oriental, and Philippines. Sampling took place from July to August 2024 across three sites at 61 meters, 113 meters and 180 meters elevation, respectively. Water quality indicators—including ammonia, phosphate, pH, electrical conductivity (EC), total dissolved solids (TDS), salinity, temperature, and water velocity—were measured to assess their impact on fish presence. There were fish species in Sites 2 and 3; however no fish was found in Site 1. Two species were identified: Barbodes sp. and Sicyopus zosterophorus. Results showed that temperature and was the most influential parameter in determining fish occurrence (Discriminant Function Analysis at p < 0.00001) gives a p-level of 0.000122. Site 2 had a temperature of 27.05°C, Site 3 exhibited a temperature of 27.64°C as opposed to Site 1 (in which no fish was found) with 26.43°C. Water velocity did not play a part in the species diversities as the time it took for water to travel in 2 meters were at 12.92, 21.02, and 8.54 minutes for Sites 1, 2, and 3 respectively.. Additionally, Site 2 exhibited higher value of EC (423.33 μS/cm), TDS (211.87 mg/L), and ammonia (0.33 mg/L, which may indicate higher nutrient availability). These parameters may support biodiversity, though these factors did not reach statistical significance. The absence of fish at Site 1 where cooler temperatures prevailed further emphasized the critical role of specific environmental conditions in shaping fish distributions. This study highlights the importance of stable, warm temperatures in promoting fish diversity in freshwater ecosystems.
Keywords: Fish Ecology, Physicochemical Parameters, Species Distribution, Habitat Suitability, Temperature and Water Velocity, Water Quality Indicators, Nutrient Availability