Levantamento da ictiofauna do ribeirão Mandaguari, bacia do rio Paranaíba, e a influência de suas cachoeiras na estruturação das assembleias de peixes

Abstract

Neotropical rivers are among the world’s greatest reservoirs of freshwater fish diversity, yet a portion of this diversity remains concealed within small tributaries. Addressing these taxonomic gaps requires inventories of such small streams, including those explored for ecotourism but whose ichthyofauna remains undocumented. Our study examines the fish assemblages in small, waterfall-bearing streams in Minas Gerais, Brazil, investigating longitudinal spatial patterns of species richness in the Ribeirão Mandaguari, a tributary of the Araguari River (Paranaíba River system) within the Upper Paraná River basin. The Ribeirão Mandaguari is a 35-km stream draining a landscape shaped by the Cerrado and Atlantic Forest biomes, traversing dissected terrain with canyons and cliffs that act as physical barriers and constrain longitudinal connectivity throughout its course. Using active and passive sampling, we recorded 19 species across 10 families, detecting a single non-native species and two potentially new species. Fish communities were unevenly distributed above, between, and below the waterfalls along the Ribeirão Mandaguari. Longitudinal richness above waterfalls differed from that observed in between and downstream reaches, a pattern consistent with spatial variation in hydraulic regime (e.g., rapids vs. lentic sections), substrate composition (e.g., rocky vs. sandy), or their combined effects which may act as environmental filters in community structuring. Our inventory indicates that small tributaries such as the Ribeirão Mandaguari harbor spatially structured ichthyofaunas, with waterfalls acting as barriers that shape assemblage composition along the longitudinal gradient. Our findings further highlight that ecotourism-frequented streams can contain underdocumented fish diversity, underscoring opportunities to align sustainable ecotourism with environmental education and conservation strategies.