<p>Floodplain systems play a key role in methane emissions. However, part of this methane can be oxidized by methanotrophic bacteria and incorporated into their biomass, thereby reducing methane release to the atmosphere. Consumers of methanotrophic bacteria, such as zooplankton and benthic invertebrates, serve as links for transferring methane-derived carbon to higher trophic levels in the food web. Here, we used carbon and nitrogen stable isotopes to investigate the role of fish communities in the incorporation of methane-derived carbon, considering the influence of feeding guilds, seasonality (wet and dry), and fish size. We hypothesized that fish relying on aquatic macroinvertebrates would exhibit a higher proportion of methane-derived carbon, particularly during the wet season. We found that between 4.80 and 17.56% (95% credible interval) of fish biomass was composed of methane-derived carbon. No differences were observed among trophic guilds, likely due to variability in habitat use and foraging strategies among species within the same guild. Species that feed on zooplankton mainly during their juvenile stages showed a decrease in methane assimilation with growth. In contrast, species that are zooplanktivorous as adults exhibited an increase. Contrary to expectations, the contribution of methane-derived carbon to fish biomass was greater during the dry season. This may reflect both turnover rate and reduced habitat availability during low water levels, which forces consumers to rely mainly on autochthonous resources such as invertebrates. These results highlight methane-derived carbon as an important energy source for floodplain consumers, demonstrating that microbial methane oxidation plays a significant role in sustaining higher trophic levels in tropical floodplain ecosystems.</p>