Fish Diversity and Habitat Complexity: The Role of Macrophytes and Physicochemical Parameters in Urban and Rural Tropical Lakes

This study highlights the impact of urbanization, agricultural runoff, and invasive species on freshwater ecosystems and aquatic biodiversity. It presents a comparative ecological assessment of two freshwater lakes in Vellore District, Tamil Nadu, India: Katpadi Lake (urban) and Saina Palayam Lake (rural). A total of 15 fish species were documented across both lakes, with Oreochromis niloticus identified as an exotic invasive species. The fish community was dominated by Cypriniformes (60%), demonstrating ecological adaptability. Diversity indices such as Shannon (H′) and Simpson (1–D) showed slight variations between the lakes. Katpadi Lake had higher total dissolved solids and conductivity, indicating greater anthropogenic influence. Ten macrophyte species, including submerged, floating-leaved, and emergent types, were observed, with their distribution differing between urban and rural sites, reflecting habitat and water-quality differences. Macrophyte diversity was greater in Saina Palayam Lake, linking habitat complexity to higher fish diversity. Submerged species such as Najas marina and Myriophyllum spicatum likely enhance habitat quality for native species. The rural wetland recorded nitrate and phosphate concentrations of 3 mg L−1 and 0.13 mg L−1, respectively, indicating measurable nutrient enrichment, while higher hardness, chloride, and ammonia levels in Katpadi Lake point to urban pollution. The findings underscore the importance of integrated monitoring of fish, macrophytes, and water quality to conserve and manage freshwater biodiversity across different environmental contexts.