Diet composition and isotopic analysis unveil trophic dynamics of a fish in a controlled flood pulse area of the Amazonia

We assessed the impact of a modified flood pulse on the trophic ecology of Ilisha amazonica by analyzing diet and resource assimilation through stable isotope analysis (δ¹³C and δ¹⁵N). Collections were conducted monthly between December 2020 and November 2021 in the Xingu River, Amazon. Stomach and muscle tissue were extracted for analysis, and both allochthonous and autochthonous resources were collected. Stomach contents of 247 specimens were analyzed and identified. The water flow regime influenced the consumption of aquatic insects, as well as the trophic niche breadth and feeding intensity of I. amazonica. Based on isotopic composition, the primary carbon sources in the species' diet originated autochthonous items, and the species exhibited a higher trophic position during the flood period. These results highlight the influence of the flood pulse, in a reduced flow environment, on the trophic dynamics of I. amazonia. Our results emphasize the importance of comprehending the interplay between consumers and resources, in areas with human influence, where impacts are practically unknown.