Stable Isotopic Analysis of Long-whiskered Catfish (Sperata aor) Otoliths for Characterization of their Habitat and Relationship with Water Temperature in the Ganges River

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.