Spatial and Seasonal Dynamics of Ichthyofaunal Diversity in the Upper Subarnarekha River, Jharkhand, India

Five stations across a 40 km stretch of the upper Subarnarekha River, Ranchi district, Jharkhand, were sampled monthly from January to December 2021. Sampling covered three seasons: pre-monsoon (January–May), monsoon (June–September), and post-monsoon (October–December). Across 60 sampling events, 62 fish species were recorded, belonging to 38 genera, 19 families, and 9 orders. Cyprinidae dominated, accounting for 28 species — 45% of total richness. The highest diversity was at Tatisilwai (Site 4; H′ = 3.21, 1–D = 0.89, J′ = 0.84), where mixed rocky-muddy substrate and well-developed macrophyte beds support a notably even assemblage. Namkum (Site 3; H′ = 2.36, 1–D = 0.79) recorded the poorest diversity; domestic sewage from Ranchi city enters this reach visibly and consistently. Post-monsoon was the richest season across all five stations (repeated-measures ANOVA, F(2,8) = 9.23, p = 0.008), driven by improved discharge, better oxygen conditions, and the appearance of monsoon-season recruits. Sensitive species — Tor tor, Bagarius bagarius, and Chitala chitala — were confined to the two least disturbed upstream stations. NMDS ordination (Bray–Curtis; stress = 0.11) separated the impacted stations (3 and 5) sharply from the intact ones (1 and 4), with sand mining and effluent discharge the primary drivers. The dataset gives a repeatable baseline for managing fish communities in this stretch of the river.