Title:Stable Isotopic Analysis of Long-whiskered Catfish (Sperata aor) Otoliths
for Characterization of their Habitat and Relationship with Water Temperature
in the Ganges River
Volume: 3
Issue: 1
Author(s): Aafaq Nazir, Prosenjit Ghosh*, Thamizharasan Sakthivel and M. Afzal Khan
Affiliation:
- Interdisciplinary Centre for Water Research, Indian Institute of Science, Bengaluru-560 012, India
- Centre for Earth Sciences, Indian Institute of Science, Bengaluru-560 012, India
Keywords:
Catfish, otoliths, stable isotopes, habitat, migration, ambient water.
Abstract:
Background: Spatial variability of stable isotope ratios in water from River Ganges is
preserved in aragonite or calcite present in otoliths and formed at equilibrium with ambient water.
This technique is used for a set of long-whiskered catfish aragonite otoliths from four different locations
along the course of the River Ganges.
Methods: Acid digestion of otolith and the analysis of δ13C and δ18O in these carbonates using an
isotope ratio mass spectrometer allowed the distinction of fish habitat and provided an idea about
environmental conditions of water along the Ganges River.
Results: The δ18O signature of otolith carbonate revealed a distinct compositional trend denoting
glacial water input in the upstream segment of the Ganges, close to the water reservoir at Narora.
However, the δ13C values remained constant, suggesting similar bicarbonate composition and food
intake along the stream length. The δ18O signature in otolith from Varanasi was unexpectedly
lighter and showed a tendency of the catfish population to migrate upstream segment of the river.
The fish from the Narora location showed the lowest δ18O values, denoting the signature of water
derived from the melting of a glacier. The heavier δ18O values were seen in the population from Kanpur.
The upstream migration of fish population is indicated from the δ18O values of a fish otolith from
Varanasi and Bhagalpur. The Varanasi location shows aberration in δ18O signature in otoliths, and
this exists because this catfish moves to other places to avoid anthropogenic stress at this location.
Conclusion: The δ18O of otolith carbonate covaries with average environmental temperature recorded
at the individual location and serves as an important thermometric measurement for marking
environmental conditions and stress in changing climatic parameters along the stream length of
River Ganges and its tributaries.