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<p>Tropical rivers face escalating threats from hydrological alteration and invasive species, yet baseline data remain scarce for seasonal systems. This study provides the first comprehensive assessment of fish assemblage dynamics in the India’s Vaigai River, integrating taxonomic, functional, and hydrological perspectives to guide conservation. Over a one-year period (June 2015–May 2016), 94,474 fish specimens were sampled, representing 147 species (139 native, 8 exotic) from 99 genera, 58 families, and 21 orders, with Perciformes (25 species), Cypriniformes (24), and Siluriformes (18) dominating the community. The&#xa0;Athankarai estuary&#xa0;emerged as a biodiversity hotspot (87 species), while midstream sites showed reduced diversity likely due to anthropogenic pressures. Notably, invasive tilapias (<i>Oreochromis</i>&#xa0;spp.) constituted&#xa0;35% of total abundance, highlighting ecological disruption, and threatening native species like&#xa0;<i>Pseudetroplus maculatus</i>&#xa0;and&#xa0;<i>Etroplus suratensis</i>. Trophic analysis revealed omnivores preferring animal material (75 species = 51%) as the most common feeding group, followed by carnivores (36 species = 24%), omnivores with plant preference (17%), and herbivores (8%), reflecting adaptive strategies to seasonal flow variability. Predatory taxa (e.g., Carangiformes, Elopiformes) exhibited higher trophic levels (≥ 3.8), indicating functional stratification within the food web. Diversity indices such as Shannon–Wiener (H'), Fisher’s alpha, and Pielou’s evenness (J') indicated stable yet seasonally modulated species diversity, while functional diversity metrics (Delta + , Lambda +) pointed to evolutionary stability and habitat-driven community differentiation. Seasonal analyses revealed&#xa0;bimodal abundance peaks&#xa0;during the Southwest Monsoon (46.6%) and Pre-Monsoon (41.6%), driven by hydrological connectivity. Cluster and multivariate ordination (nMDS, MDS) analyses revealed significant seasonal turnover in fish communities (46–96% similarity), highlighting the influence of hydrological variability on biodiversity patterns. Principal Component Analysis (PCA) revealed hydrological seasonality as the dominant habitat specialized key driver of fish assemblage patterns, with PC1 (98.8%) separating high-flow (Southwest and Pre-Monsoon) periods dominated by <i>Oreochromis</i> spp, <i>Cirrhinus mrigala</i>, and <i>Glossogobius giuris</i>, from low-flow (Post- and Northeast Monsoon) periods. PC2 (0.9%) distinguished estuarine species (<i>Megalops cyprinoides</i>, <i>Nematalosa nasus</i>) from pelagics (<i>Thryssa vitrirostris</i>, <i>Stolephorus commersonnii</i>), while PC3 (0.3%) revealed trophic differentiation between detritivores and piscivorous small pelagics. Vaigai River's ecological complexity demands flow-dependent, site-specific conservation controlling invasives, preserving habitats, and maintaining hydrological connectivity amid growing anthropogenic and climate pressures.</p>

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Fish Assemblage Dynamics, Tilapia Invasion, Trophic Guilds, and Conservation Priorities in the Hydrologically Fragmented Vaigai River-Estuary Continuum, India

  • 期刊论文

  • 发表日期：

    2025年8月8日

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  • Mogalekar H.S,
  • Sudhan C,
  • Katare M.B,
  • Swami A.M

摘要

Tropical rivers face escalating threats from hydrological alteration and invasive species, yet baseline data remain scarce for seasonal systems. This study provides the first comprehensive assessment of fish assemblage dynamics in the India’s Vaigai River, integrating taxonomic, functional, and hydrological perspectives to guide conservation. Over a one-year period (June 2015–May 2016), 94,474 fish specimens were sampled, representing 147 species (139 native, 8 exotic) from 99 genera, 58 families, and 21 orders, with Perciformes (25 species), Cypriniformes (24), and Siluriformes (18) dominating the community. The Athankarai estuary emerged as a biodiversity hotspot (87 species), while midstream sites showed reduced diversity likely due to anthropogenic pressures. Notably, invasive tilapias (Oreochromis spp.) constituted 35% of total abundance, highlighting ecological disruption, and threatening native species like Pseudetroplus maculatus and Etroplus suratensis. Trophic analysis revealed omnivores preferring animal material (75 species = 51%) as the most common feeding group, followed by carnivores (36 species = 24%), omnivores with plant preference (17%), and herbivores (8%), reflecting adaptive strategies to seasonal flow variability. Predatory taxa (e.g., Carangiformes, Elopiformes) exhibited higher trophic levels (≥ 3.8), indicating functional stratification within the food web. Diversity indices such as Shannon–Wiener (H'), Fisher’s alpha, and Pielou’s evenness (J') indicated stable yet seasonally modulated species diversity, while functional diversity metrics (Delta + , Lambda +) pointed to evolutionary stability and habitat-driven community differentiation. Seasonal analyses revealed bimodal abundance peaks during the Southwest Monsoon (46.6%) and Pre-Monsoon (41.6%), driven by hydrological connectivity. Cluster and multivariate ordination (nMDS, MDS) analyses revealed significant seasonal turnover in fish communities (46–96% similarity), highlighting the influence of hydrological variability on biodiversity patterns. Principal Component Analysis (PCA) revealed hydrological seasonality as the dominant habitat specialized key driver of fish assemblage patterns, with PC1 (98.8%) separating high-flow (Southwest and Pre-Monsoon) periods dominated by Oreochromis spp, Cirrhinus mrigala, and Glossogobius giuris, from low-flow (Post- and Northeast Monsoon) periods. PC2 (0.9%) distinguished estuarine species (Megalops cyprinoides, Nematalosa nasus) from pelagics (Thryssa vitrirostris, Stolephorus commersonnii), while PC3 (0.3%) revealed trophic differentiation between detritivores and piscivorous small pelagics. Vaigai River's ecological complexity demands flow-dependent, site-specific conservation controlling invasives, preserving habitats, and maintaining hydrological connectivity amid growing anthropogenic and climate pressures.