Detecting natural hybridization among Indian major carps through advance morphometric approach

Abstract

Interspecific natural hybridization is an indicator of altered ecosystem. Habitat destruction increases competition with fish species in close proximity for spawning habitat with overlapping reproductive activities, thereby causing natural hybridization. This study is first investigation on detecting hybrids among Indian major carps (Labeo rohita, Cirrhinus mrigala and Gibelion catla) from the Ganga River by applying a cost-effective method, “Geometric Morphometrics”. The relative warps (RW), principal component analysis (PCA) and canonical variate analysis (CVA) were employed on superimposed images to determine morphometric variations. Deformation grid of RW showed that G. catla and hybrid specimens have a deeper whereas L. rohita and C. mrigala specimens have slender body profile. The PCA showed separation among specimens of four groups (three species and one hybrid) with slight overlap between G. catla and hybrid. CVA extracted Mahalanobis and Procrustes distances among four non-overlapping groups found to be highly significant (P < 0.0001) with hybrid specimens lying between position of L. rohita and G. catla specimens in close proximity to G. catla, suggesting that hybrids are product of crossing between L. rohita and G. catla. The CVA separated four groups with 100.00% classification, indicating that all the three species and hybrid were clearly distinct from each other. In this study, all the four specimens of hybrid were caught from upstream of four barrages (Bijnor, Narora, Kanpur and Farakka) commissioned along the middle and lower stretch of the Ganga River. This suggests that, barrages obstruct upward movement of fish population and impact on reproductive activities, thereby increases possibilities of natural hybridization among these species.