Fish Community Structure and Diversity Along the Batang Kuranji Watershed Following the 2025 Flash Flood in Padang City, Indonesia
Abstract
Flash floods are major disturbances affecting river ecosystems by altering habitat characteristics, water quality, and aquatic community structure. However, information on post-flood fish community responses in tropical watersheds remains limited. This study provides an early assessment of fish community responses following the 2025 flash flood in the Batang Kuranji Watershed, providing baseline information on fish community conditions after a major hydrological disturbance. Such information is ecologically important for understanding habitat alteration and the initial capacity of riverine fish communities to persist following flood disturbance. Field sampling was conducted in March 2026 at three representative stations in the upstream, midstream, and estuarine sections using purposive sampling. Fish were collected and identified, while temperature, pH, dissolved oxygen (DO), turbidity, and current velocity were measured in situ. Community structure was assessed using the Shannon–Wiener diversity index, relative abundance, Bray–Curtis and Jaccard similarity indices, and one-way ANOVA followed by Tukey's test. A total of 162 individuals representing 10 species were recorded. Rasbora sp. was dominant (25.93%), followed by Oreochromis niloticus (20.37%) and Osteochilus hasselti (14.81%). Fish abundance increased from upstream (39) to midstream (56) and estuary (67), with significant differences among stations (p < 0.05). Shannon–Wiener diversity was moderate at all stations (H′ = 1.26–1.50), with the highest value at the estuary. Community similarity was highest between upstream and midstream (Bray–Curtis = 0.52; Jaccard = 0.33), while upstream–estuary similarity was 0.00 for both indices. Water quality remained suitable for fish, although turbidity increased and current velocity decreased toward the estuary. These findings provide a baseline for post-flood ecological assessment and watershed management.