Assimilation of methane-derived carbon by native and non-native fish in a Neotropical reservoir

Artificial reservoirs are among the main global producers of methane. However, this methane can be oxidized by methanotrophic bacteria and incorporated into the food web through aquatic organisms, such as zooplankton, insect larvae, and oligochaetes, that feed on these bacteria. Non-native apex fish species may change this dynamic due to their high predation rates on meso-predators, which primarily feed on aquatic invertebrates. Thus, we aimed to investigate the proportion of methane-derived carbon in the fish community of an artificial reservoir using δ 13 C analysis and to examine the role of native and non-native consumers in this process. We found methane-derived carbon in all analyzed fish species, including both meso-predators and apex consumers, with proportions ranging from 5% to 12%. Additionally, we found that the non-native apex predator Micropterus salmoides primarily feeds on Psalidodon minor , the main assimilator of methane-derived carbon. The high predation pressure on P. minor poses a significant threat to the methane cycle, as M. salmoides may trigger a cascade effect, reducing P. minor populations and, consequently, the incorporation of methane-derived carbon into the food web. Therefore, this study underscores the crucial role of Neotropical fish species in methane-derived carbon assimilation and highlights the threat that non-native species pose to this process. These results underscore the importance of conserving fish communities to help mitigate methane emissions into the atmosphere.