Comparative Study of Water Quality and Fish Community Structure in Gangasandra and Melekote Tanks, Tumkur District

Water reservoirs in semi-arid regions like Karnataka, India, are vital for biodiversity conservation, irrigation, and potable water supply. This study investigates the seasonal variations in physicochemical parameters, heavy metal contamination, and fish population dynamics in two perennial reservoirs-Gangasandra and Melekote tanks, over a two-year period (May 2022 to April 2024). Water quality parameters including temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), turbidity, total dissolved solids (TDS), total hardness, alkalinity, and nutrients were monitored monthly using standardized protocols (APHA, 2017). Heavy metals (Fe, Cd, Mn, and others) were quantified via atomic absorption spectroscopy. Fish populations were sampled seasonally using multi-mesh gill nets, with Oreochromis mossambicus as a focal species for abundance estimation. Results showed typical monsoonal fluctuations: temperature ranged from 20°C in winter to 25°C pre-monsoon; pH remained near-neutral with minor seasonal shifts; EC, turbidity, and TDS peaked post-monsoon due to runoff inputs. Melekote tank exhibited higher mineral and organic loading, reflected in elevated total hardness (288–358 mg/L) and biological oxygen demand (BOD) values, likely influenced by adjacent sewage treatment. Heavy metal concentrations were within acceptable limits but highlighted potential bioaccumulation risks. Fish community structure varied seasonally, correlating with changing water quality. These findings underscore the influence of hydrological cycles and anthropogenic pressures on reservoir ecosystem health. The comparative analysis provides crucial baseline data for sustainable management and conservation of semi-arid reservoir ecosystems in Karnataka.