Abstract
The fish fauna from the Lower Iguaçu River and tributaries upstream of the Iguaçu Falls, the last free-flowing river stretch, were investigated. Twenty five sites in tributaries and the main channel were sampled between 2010 and 2016 using several kinds of fishing gear. The species were categorized according to their size, origin, and conservation status. Species richness and abundance in the main channel and tributaries were compared. In total, 87,702 specimens were recorded, comprising 76 species, 25 families, 53 genera, and eight orders. Characiformes and Siluriformes were the richest orders, representing 92% of the total specimens; Characidae, Cichlidae, Pimelodidae, and Loricariidae were the richest families. The fish fauna was composed of small and medium-sized species and included endemic (42%), autochthonous (24%), allochthonous (21%), and exotic (9%) species, as well as hybrids (4%). Significant differences in the relative numerical abundance of species were found among sites. Ancistrus mullerae and Rhamdia branneri (endemic) were indicator species for tributaries inside of Iguaçu National Park (INP), while Phalloceros harpagos (autochthonous) and Ictalurus punctatus (exotic) for tributaries outside of INP and Odontesthes bonariensis (allochthonous) for the main channel. The last dam-free stretch of the Lower Iguaçu River and tributaries upstream the Iguaçu Falls exhibits a rich endemic fish fauna, including some rare, endangered species (Steindachneridion melanodermatum, Gymnogeophagus taroba, and Psalidodon gymnogenys). These findings are essential to predict and understand the effects caused by the new Baixo Iguaçu Hydroelectric Power Plant and highlight the importance of tributaries and Iguaçu National Park for conservation of endemic species.
Highlights
The high diversity of species in the Neotropical region is recognized worldwide
The number of identified species accounted for 72% of the number of species observed in a previous study for the Lower Iguaçu basin (Baumgartner et al 2012), of which seven species had not been recorded (Schizodon borellii, Charax stenopterus, Leiarius marmoratus, Poecilia reticulata, Crenicichla lepidota, C. tapii, and C. tuca)
The last dam-free stretch of the Lower Iguaçu River upstream of the Iguaçu Falls exhibits a rich endemic fish fauna, rare endangered species restricted to this region, and new species for science
Summary
The high diversity of species in the Neotropical region is recognized worldwide This region currently has more than 5,160 species of freshwater fish and may have as many as 9,000 species (Reis et al 2016). Endemism is a well-recognized feature of the Iguaçu river basin (Baumgartner et al 2012), which has led to its classification as a distinct ecoregion for freshwater fish conservation (Abell et al 2008). This unique fauna arose from the isolation of this basin caused by the formation of the Iguaçu Falls some 22 million years ago (OligoMiocene period) (Severi and Cordeiro 1994). Many of these species have been described in the last decade, taxonomic problems remain (Baumgartner et al 2012), indicating that the diversity may be underestimated
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