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Assessment of trophic polymorphism in the Himalayan fish Tor putitora

Martin, Ian



An investigation into intra-specific morphological variation in Tor putitora fish from the Mahakali River in western Nepal was carried out. Three main hypotheses were tested: i) two distinct variants, one with thin lips and a forward-facing mouth (Type A), another with thick lips, an extended protrusion known as a mental lobe and more ventrally oriented mouth (Type B), can be distinguished by meristic, allometric or landmark-based morphometric analyses; ii) differences in ecological conditions in spatially separated breeding streams, potentially linked to environmentally influenced morphological variation, can be observed; iii) differences in stable isotope ratios of carbon and nitrogen obtained from fish scales, and therefore evidence of dietary divergence, are evident between the two morphotypes.

Meristic and allometric analyses provided no evidence of distinguishing features between the morphotypes, however the landmark-based morphometric analysis produced very strong evidence that the two morphotypes clearly differ in shape and features of the head and mouthparts. Analysis of the physico-chemical conditions and aquatic invertebrate communities in the spatially separated breeding streams produced results which refuted the second hypothesis but suggested strongly that differences between seasons (snow-melt and post-monsoon) were statistically significant and suggested an alternative hypothesis that breeding events may be segregated temporally, rather than spatially. Stable isotope analysis uncovered statistically significant differences in nitrogen isotope ratios which supported the hypothesis that the two morphotypes display divergence in diet, very likely linked to the morphological variation in the head and mouthparts.

This examination provides evidence of trophic polymorphism in T. putitora and illuminates the path to further studies of this phenomenon which has been observed in several other species of the same genus across south and southeast Asia.

Thesis Type Thesis
Deposit Date Nov 7, 2022
Publicly Available Date Nov 7, 2022
Public URL
Award Date Jul 7, 2022


Assessment of trophic polymorphism in the Himalayan fish Tor putitora (2.6 Mb)

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