From the headwaters to the Iguassu Falls: Inventory of the ichthyofauna in the Iguassu River basin shows increasing percentages of nonnative species

Abstract

Knowledge of the ichthyofauna of a hydrographic basin is the minimum necessary condition for the implementation of any measures for the exploration, management or preservation of water and fishing resources. Despite its relevance, the number of fish species across the Iguassu River basin is still uncertain. Thus, the objective of this study was to compile the fish species that occur in the extensive stretch of the basin above the Iguassu Falls. In addition, we recorded the level of threat of extinction for native species, the origin of nonnative species, and their main vectors of introduction. To achieve this goal, a survey was carried out through consultations with ichthyological collections as well as online databases. Also, a literature review was conducted using the search platforms Thomson Reuters, SciELO and Elsevier’s ScienceDirect to locate all articles published by March 2020 that addressed the topic “ichthyofauna in the Iguassu River basin”. The survey compiled a total of 133 fish species distributed in nine orders, 29 families and 72 genera. Seventy-nine fish species were recorded that occur throughout the entire length of the basin, 119 species that occur in the hydrographic units of the middle and lower Iguassu River (40 exclusive) and 93 species that occur in the hydrographic unit of the upper Iguassu River (14 exclusive). The endemism rate shown here for the Iguassu River basin (approximately 69%) contrasts with the 40 nonnative fish species recorded (approximately 30% of the total species in the basin). Successive impoundments, reductions in habitat quality and the increase in the number of nonnative species are the main threats to native species, especially to the endemic species; approximately 20% of these species were listed in some category of threat of extinction. We emphasize that constant monitoring of ichthyofauna is necessary to discover putatively undescribed species, as well as for the application of management strategies to mitigate the negative effects and promote the control of the spread of nonnative species.

New conservation opportunities: Using citizen science in monitoring non‐native species in Neotropical region

“…The Iguaçu River basin (states of Paraná and Santa Catarina, Brazil and Argentina) is considered a global biodiversity hotspot (Abell et al, 2008), where 70% of species are considered endemic to the basin (Baumgartner et al, 2012;Daga et al, 2016;Garavello & Sampaio, 2010;Mezzaroba et al, 2021;Reis et al, 2020). However, this region is threatened with huge losses of its endemic species, primarily because of the introduction of non-native species (Daga et al, 2016;Gubiani et al, 2010;Mezzaroba et al, 2021). The presence of "dourado," Salminus brasiliensis, in the Iguaçu River basin represents a high risk, especially for smaller species already threatened with extinction (Geller et al, 2020).…”

Here comes the large catfish “jaú” Zungaro jahu (Ihering 1898) (Teleostei, Pimelodidae): a new alarming case of fish introduction in a high-endemism Neotropical ecoregion

“…Current records indicate that the number of non-native fishes reached an expressive rate of 30% (40 species) of the total species recorded in this aquatic ecoregion (Gubiani et al, 2018;Mezzaroba et al, 2021). The introduction of species, in association with other environmental changes, such as deforestation, urbanization, dams, and pollution, impose severe threats to the native ichthyofauna, especially to endemic species (Baumgartner et al, 2012;Daga & Gubiani, 2012;Daga et al, 2016;Neves et al, 2018;Ganassin et al, 2021b;Mezzaroba et al, 2021). Over the last few decades, there has been a marked population decline [see Ganassin et al (2021b)] and potential risk of extinction of native/endemic fish species in the Iguaçu River basin (Instituto Chico Mendes de Conservação da Biodiversidade, 2018).…”

“…Acta Limnologica Brasiliensia, 2022, vol. 34, e25 Daga & Gubiani (2012); Daga et al (2016); Mezzaroba et al (2021); Pini et al (2021)]. Unfortunately, the introduction of fish species in this aquatic ecoregion is subsidized by supposed local economic attractions, sport-fishing programs, and even by the proposals of new environmental laws [see Vitule et al (2014); Ribeiro et al (2017); Geller et al (2021a, b)].…”

“…Since 1944, the number of fish introductions in the Iguaçu River basin has shown a steady increase (Daga et al, 2016). Current records indicate that the number of non-native fishes reached an expressive rate of 30% (40 species) of the total species recorded in this aquatic ecoregion (Gubiani et al, 2018;Mezzaroba et al, 2021). The introduction of species, in association with other environmental changes, such as deforestation, urbanization, dams, and pollution, impose severe threats to the native ichthyofauna, especially to endemic species (Baumgartner et al, 2012;Daga & Gubiani, 2012;Daga et al, 2016;Neves et al, 2018;Ganassin et al, 2021b;Mezzaroba et al, 2021).…”

“…The fish fauna from the Iguaçu River basin in Brazil, where there is a significant number of endemic species [64, according to Reis et al (2020); Mezzaroba et al (2021)] is severely threatened by impoundments and the introduction of nonnative species [see Baumgartner et al (2012);…”