Impacts of roads on the body condition of Amazonian stream fish

Drager, Dennys Heilbuth Cachapuz and Leal, Cecília and Salvador, Gilberto Nepomuceno and Carvalho, Débora Reis de and Pompeu, Paulo Santos and Ferraz, Gabriel Oliveira and Brejão, Gabriel Lourenço and Basílio, Pedro Henrique dos Santos and Rodrigues-Filho, Carlos Alberto de Sousa and Ferraz, Silvio Frosini de Barros and Maeoka, Leonardo Toshiaki Yabuke and Zuanon, Jansen and Montag, Luciano Fogaça de Assis and Alves Filho, Marcos Angelo and Leitão, Rafael Pereira (2025) Impacts of roads on the body condition of Amazonian stream fish. Neotropical Ichthyology, 23 (4): e250078. ISSN 1679-6225

Abstract

The Neotropical ichthyofauna has been degraded by multiple anthropogenic alterations. Despite advances in understanding their negative effects on species assemblages, little is known about how such changes affect fish’ nutritional status. We tested the effects of road density, road-stream crossings density, and riparian deforestation on the condition factor of Amazonian fish species. We expected a decline in the condition factor for an allochthonous insectivore, an increase for a detritivore, and no effect on omnivorous species, across 32 headwater streams in the Amazon agricultural frontier. Our predictions were partially supported: The insectivorous species was possibly negatively affected by dietary impoverishment caused by increased siltation and the formation of deeper, slower habitats associated with road expansion, and none of the variables significantly influenced the omnivorous species. Contrary to our expectations, landscape degradation and stream fragmentation did not lead to an increase in the condition factor of the detritivorous species. These results may be explained by the differential responses of species, mediated by their traits, to environmental changes. Long-term monitoring will be essential to enhance the predictive power of this tool in detecting responses to anthropogenic changes in aquatic ecosystems.