Non-native fish invasions of a Neotropical ecoregion with high endemism: a review of the Iguacu River

The freshwater fish fauna of the Neotropics comprises one of the most diverse ichthyofaunas globally. The Iguacu ecoregion of the Neotropics includes about 100 described species, of which approximate to 70% are endemic and the majority of these are considered to be threatened with extinction. As is the case in freshwaters worldwide, the Iguacu ecoregion has been strongly impacted by a variety of factors, including urbanization, agriculture, the construction of dams and the introduction of non-native species. There is, however, a paucity of information on fish invasions and their impacts in the Iguacu ecoregion. To address this knowledge gap an exhaustive literature review was conducted to determine the extent of introductions, the main vectors of introductions and the major risks associated with the introduction of non-native fish into the Iguacu ecoregion. A total of 41 studies concerning non-native fish in the Iguacu ecoregion were found, the majority (56.1%) from lists of species and first records of non-native species; while 29.3% of the studies only mentioned possible negative impacts of non-native species and 14.6% of studies evaluated, indirectly, the impacts of non-native species. The Iguacu ecoregion has a long history of fish introductions, beginning with the first record of the "common carp" Cyprinus carpio in 1944, and continuing to the recent record, in 2012, of Steindachnerina brevipinna. Since 1944, 29 non-native species have been introduced, 19 from different ecoregions of the Neotropics, and 10 introduced from other zoogeographic regions (Ctenopharyngodon idella, C. carpio, Hypophthalmichthys molitrix, H. nobilis and Misgurnus anguillicaudatus from Palearctic region; Clarias gariepinus, Oreochromis niloticus and Tilapia rendalli introduced from Ethiopian region, and Ictalurus punctatus and Micropterus salmoides from Nearctic region). The main vector of introduction was aquaculture, with the aquarium trade, baiting, sport fishing and stocking also playing roles. Studies indirectly investigating the establishment and spread of the introduced species in the Iguacu ecoregion found nine non-native species which were considered established. Moreover, studies evaluating the impact of non-native species have investigated changes in the feeding habits of non-native species, suggesting competition with native species for food resources, and the increase in the number of fish species introduced over time. The impacts of non-native fishes, often associated with other environmental changes, such as the construction of dams and pollution in the Iguacu ecoregion, may have severe consequences for the endemic fish fauna, resulting in the further decline and potential extinction of native species.