Feeding ecology of a detritivorous fish in controlled flood pulse area in the Amazon revealed by stomach content and stable isotopes analyses

Abstract

This study aimed to assess the trophic dynamics of a detritivorous species throughout various hydrological periods in a reduced flow section, Volta Grande, of the Xingu River. Specimens were collected between December 2020 and November 2021 using gill nets. Stomachs were dissected to examine their contents, and muscle tissue samples were collected for isotopic analyses of δ¹³C and δ¹⁵N. The diet across hydrological periods was analysed using permutational multivariate analysis of variance. Variation in trophic niche breadth was evaluated using permutational dispersion analysis with food importance values. Feeding intensity was evaluated using the repletion index, and its variation across periods was tested using Kruskal-Wallis. Isotopic structure across hydrological periods was evaluated through analysis of variance. Isotopic niche overlap was calculated using the corrected standard ellipse area metric. Mixed effect models were employed to estimate the contributions of basal resources assimilated by the species across periods. Our results revealed stable patterns in the diet and energy sources of the species across different hydrological periods. Given the escalating impact of human activities on natural seasonal variations in rivers, conducting detailed trophic studies and employing precise methods to reconstruct food webs and energy flow in altered aquatic ecosystems are essential. This information is crucial for guiding measures aimed at protecting and conserving these environments and the ichthyofauna reliant on them.