Hydrology–Biodiversity Linkages in Gose Khurd Reservoir: Long‐Term Spatiotemporal Dynamics of Fish Communities

Understanding how seasonal hydrologic forcing reorganizes habitat conditions is essential for managing fish biodiversity in tropical reservoirs. We assessed spatial and temporal dynamics of fish assemblages in the Gose Khurd Reservoir (Wainganga River basin), Maharashtra, India, using an 18‐month monthly survey (January 2024–June 2025) across five stations representing major habitat zones. Fish were sampled using multiple gears to reduce selectivity bias, and concurrent measurements were made of key hydroecological variables (water temperature, pH, dissolved oxygen, electrical conductivity, Secchi transparency and alkalinity). Across 90 station–month samples, we recorded 75 species (12 orders, 21 families and 51 genera) and 229,831 individuals, with a strongly uneven dominance structure led by Salmophasia bacaila , Ambassis nama , Salmostoma boopis , Osteobrama vigorsii and Clupisoma bastari . Environmental conditions varied markedly among monsoon‐defined seasons, including broad shifts in transparency (60–218 cm), dissolved oxygen (2.30–6.71 mg/L) and alkalinity (87–177 mg/L). Multivariate analyses (principal component analysis [PCA], canonical correspondence analysis [CCA] and nonmetric multidimensional scaling [nMDS]) identified transparency, alkalinity and dissolved oxygen as the primary gradients associated with assemblage organization, whereas electrical conductivity and temperature had weaker to moderate effects, and pH was comparatively minor. Assemblages clustered by season in ordination space (nMDS stress = 0.14), and Permutational Multivariate Analysis of Variance (PERMANOVA) confirmed significant seasonal differences in composition (pseudo‐ F = 2.26, p = 0.001). Overall, the results indicate that monsoon‐driven hydroecological transitions act as environmental filters that shape community structure and seasonal turnover. These findings support multiseason monitoring as a basis for biodiversity assessment and reservoir fisheries management under strong climatic seasonality.