A Comprehensive Review of Morphometric and Meristic Variations in Freshwater Fishes: Trends, Environmental Drivers and Taxonomic Implications

Abstract

Morphometric and meristic traits offer powerful, cost-effective tools for analysing phenotypic variation, stock structure, and environmental adaptation in freshwater fishes. This review synthesizes findings from more than thirty studies published between 2012 and 2024, covering diverse taxa across Asia, Africa, and the Middle East. The literature reveals strong habitat-driven morphological plasticity, particularly in riverine species exposed to hydrodynamic forces, ecological gradients, and climatic variability. Morphometric traits, which respond rapidly to ecological pressures, consistently differentiated populations of Channa striata, Wallago attu, Schizothorax spp., Clupisoma garua, and several others. Meristic traits, although more genetically stable, also reflected population-level divergence under varied developmental and environmental conditions. Integrating these patterns, the review highlights the importance of morphology for taxonomy, species discovery, biodiversity monitoring, and sustainable fisheries management. Despite methodological challenges—including inconsistent measurement protocols and limited geographic coverage—advances in geometric morphometrics, molecular barcoding, and multivariate analytics have strengthened morphological research. The review emphasizes the need for standardized methodologies and integrated approaches to better understand phenotypic diversity and ensure the conservation of freshwater fish resources in rapidly changing ecosystems.