Curimatidae

Curimatids are widespread in the Neotropical region (Vari, 2003). However, only one Steindachnerina species was known to be present in the upper rio Paraná: S. insculpta, which is abundant in the entire basin. Late last century, another congener was described from the rio Corumbá (an affluent of the rio Paranaíba): S. corumbae, which is endemic to the rio Paraná headwaters (Pavanelli & Britski, 1999). Steindachnerina brevipinna, which was restricted to the Paraná-Paraguay system below Sete Quedas (Vari, 2003), successfully colonized the upper rio Paraná basin after the construction of the Itaipu Dam, and it is now found syntopically with S. insculpta. One of the main differences between the two congeners is a round black blotch on the dorsal fin rays of S. brevipinna that is lacking in S. insculpta. Captures of several individuals with faded blotches caused uncertainties about the existence of hybrids between these species. To elucidate this issue, samples of individuals displaying a very dark, faded or completely absent blotches were compared by the random amplified polymorphic DNA (RAPD) technique in addition to being morphologically analyzed. Occurrences of both species were confirmed, and individuals with a faded blotch were attributed to S. brevipinna rather than hybrids (Oliveira et al., 2002).