Investigating the trophic ecology of freshwater fish communities from central and eastern Indian streams using stable isotope analysis

Stable isotope analysis (SIA) has been used over the last decade to decipher trophic relationships between organisms, espe- cially in freshwater and marine systems. Using SIA to understand food web patterns in stream communities, we present a first time investigation on trophic structure of fish communities from two ecoregions in eastern and central India. This study is based on pooled pre-monsoon samples from each region, which were analyzed for their isotopic carbon and nitrogen. Fish dietary data from secondary literature and available databases based on their known gut content analysis were included for calculating average food web lengths. Despite being located within the tropics and therefore from similar ecological and climatic conditions, subtle differences were observed in the food web shape and food web lengths of fish communities from the two regions. Food web length was longer in central Indian streams compared to eastern Indian streams. Higher trophic diversity and lower trophic redundancy among fishes of central India were indicative of specialized feeding. On the other hand, a greater utilization of diverse basal resources indicated feeding niche overlap and greater omnivory among fishes in eastern India. Benthopelagic fishes were found to be the largest guild and occupied the largest area as well as maximum carbon and nitrogen ranges. In addition to providing an understanding of the trophic patterns in tropical stream ecosystems, our work serves as a baseline for future studies on trophic structure in Indian stream fish communities