Vertebral monstrosities: phenotypically shortened fish with deformed vertebrae in endemic fish genus Hypselobarbus (Bleeker, 1860), (Teleostei: Cyprinidae) from Western Ghats, India

Abstract Background Fish with vertebral monstrosities are very rare in the wild, as those individuals in the natural populations tend to perform poorly to survive in any ecosystem. Species of the fish genus Hypselobarbus as reported (Bleeker in De visschen van den Indischen Archipel, Lange, 1860) are freshwater endemic barbs of Western Ghats and peninsular India. Four species of the genus, namely Hypselobarbus dobsoni (Krishna carp), H. jerdoni (Jerdon’s Carp), H. lithopidos (Canara barb) and H. thomassi (Red Canarese barb), were collected from three different river systems of the Western Ghats biodiversity hotspot of India. Some individuals were found to be different from normal specimens, with extremely large body depth compared to normal specimens. The study was initiated with the aim of bringing an understanding on monstrosities of these four species along with identifying the normal and abnormal individuals in an integrated approach; employing traditional morphometry, X-ray imaging and barcoding mtDNA COI X-ray imaging could elucidate the vertebral monstrosities, which are discussed in detail. The mtDNA COI gene sequences generated were used to draw conclusions on identity of both normal and deformed individuals. Results The phenotypic deformities have led to deepening of the body with a more robust and reduced length which is evident from the morphometric comparison of normal specimens with deformed ones. The radiographic images revealed reduced intra-vertebral space in comparison with the normal vertebrae, deformed vertebrae were between 25 and 32, showing significantly altered intra-vertebral space. Slight genetic divergence of 1.1% between normal and deformed specimens in mitochondrial DNA COI gene of H. lithopidos and H. thomassi and no divergence in H. dobsoni and H. jerdoni were also observed . Conclusion The specimens were collected from areas with high anthropogenic stresses, abate water quality, and habitat, which could be possible reasons of appearance of individuals with deformed vertebrae. Several environmental and genetic factors might have influenced the development of these robust short-bodied phenotypes in these rivers and possess slight genetic divergence from normal specimens. However, these deformities may also be the result of the stress during embryonic and early life stages in the wild.