Crislei Larentis, Mara Cristina Baldasso, Bruna Caroline Kotz Kliemann, Mayara Pereira Neves, Arielli Giachini Zavaski, Leticia Mazzuco Sandri, Ana Cristina Ribeiro, Daniel Pereira de Sousa Simões Xavier, Giovanni de Oliveira Nagasawa Costa, Rosilene Luciana Delariva
Members of the order Cyprinodontiformes are cosmopolitan in tropical and temperate latitudes, widely distributed in freshwater and saline habitats (Rosen & Bailey, 1963). In this order, the family Poeciliidae comprises 42 genera with about 353 species (Nelson, Grande, & Wilson, 2016), which are small and laterally compressed fishes, with body form ranging from extremely elongated (e.g., Tomeurus) to deep‐bodied (e.g., Phallichthys, Carlhubbsia) (Lucinda,
2003). Some species have been introduced in many countries by ornamental aquarists (Magalhães & Jacobi, 2017), and as an alternative measure to biological control of mosquitoes (Azevedo‐Santos, Vitule, Pelicice, & García‐berthou, 2016). Seven species were already registered in Brazilian headwater streams (Magalhães & Jacobi, 2017). The main introduction vector of Poecilids in Brazil is the aquarium hobby, a practice that has gained popularity because of the ease in obtaining a diversity of attractive species. However, certain difficulties in the care of ornamental fish, such as the excessive growth and aggressiveness of some species, motivate the aquarists to release their unwanted fishes into artificial or natural aquatic environments (Magalhães & Jacobi, 2013). This illegal release has introduced not only Poecilia reticulata Peters, 1859 into Brazilian streams, but also some species of Xiphophorus (Magalhães & Jacobi, 2017).
The drainage area of the Iguazu River Basin cross different geological and geomorphological units (Parolin, Ribeiro, & Leandrini, 2010). It has many waterfalls, most notably the Iguazu Falls (82 m high), formed in a geological event dating from the Cretaceous period (Parolin et al., 2010), and which likely generated a cladogenic event for many fish species in the Iguazu River. These waterfalls, located near the mouth of this river, are classified as level‐three barriers for the movement of fish, promoting the isolation of the fish fauna. Additionally, there are more six artificial barriers along the Iguazu River (Baixo Iguaçu, 2019; Baumgartner et al., 2012). The presence of these barriers ensures that the species do not colonize other regions, unless they are aided by human intervention (Rahel, 2007). Such geographical isolation guaranteed to the Iguazu River Basin a small‐sized fish fauna, highly endemic (Baumgartner et al., 2012), and therefore a global biodiversity ecoregion (Abell et al., 2008; Hales & Petry, 2015). This basin is particularly vulnerable to non‐native fish introductions, however, a recent study showed that 27 fish species have already been introduced in the Iguazu River Basin (Gubiani et al., 2018). Such introductions cause negative impacts on endemic fish fauna, increasing the risk of extinctions (Daga, Debona, Abilhoa, Gubiani, & Vitule, 2016; Gubiani et al., 2018).
FIGURE 1 Geographic location of sampling sites (black circles) in the lower Iguazu River Basin, highlighting the Bom Retiro stream (black star)
FIGURE 2 Xiphophorus hellerii sampled in Bom Retiro stream, lower Iguazu River Basin, Brazil. (a) adult individual (68.8 mm) (TL); (b) juvenile individual (40 mm) (TL). (TL‐total length)