Population discrimination of Batchwa vacha (Eutropiichthys vacha) based on body shape metrics across diverse aquatic habitats in Bangladesh: A multivariate study

Abstract

The Batchwa vacha fish (Eutropiichthys vacha) is an ecologically significant freshwater catfish species that inhabits a wide range of coastal, riverine, and estuarine environments across Bangladesh. Comprehending the degree of habitat-induced phenotypic variation in this species is essential for efficient fisheries management, stock evaluation, and conservation efforts. However, there is limited research on its morphological variation across different environmental conditions. This study investigates the hypothesis that significant morphological differences exist among E. vacha populations inhabiting geographically and ecologically diverse habitats in Bangladesh. In September-October 2025, 317 specimens were acquired from five diverse habitats: Kaptai Lake, Hakaluki Haor, and the Padma, Meghna, and Jamuna rivers, encompassing both lotic and lentic ecosystems. Geometric morphometric analysis (GMA), employing landmark-based digital imaging, was utilized to quantify small but biologically significant differences in body shape. The findings indicated substantial physical variation among populations, with distinct differences between lotic and lentic groups. This suggests that habitat-specific ecological pressures, such as flow regimes, may drive adaptive morphological responses in E. vacha. key morphological traits, including snout shape, dorsal-abdominal width, caudal peduncle depth, and overall head configuration, exhibited pronounced differences. These traits are typically linked to swimming performance, feeding strategies, and habitat use, underscoring their ecological relevance. Discriminant Function Analysis (DFA) confirmed substantial morphological divergence between populations from geographically distant regions, such as Kaptai Lake and the Jamuna River, while populations from nearby systems showed less pronounced differences, indicating potential connectivity or shared environmental factors. The high classification accuracy achieved by the DFA further emphasizes the effectiveness of geometric morphometrics in detecting even subtle morphological differences across populations. This study also emphasizes the importance of habitat-induced morphological diversity in E. vacha, and demonstrates how geometric morphometrics is helpful to assess species adaptability to different environmental conditions. These results advance our understanding of the population structure of E. vacha and provide important implications for long-term viability of this ecologically and commercially important species.