Over the past few decades, South American Rivers, including the Paraná River system, have been intensely impacted by dam constructions. To mitigate adverse impacts, fish passages were incorporated into two large dams on the Paraná River (Itaipu and Porto Primavera) to reestablish longitudinal connectivity, which is very important for conserving populations of migratory fish species. The aim of this study was to estimate genetic diversity, population differentiation and gene flow, using microsatellites markers and mitochondrial haplotypes (D-loop), in populations of Prochilodus lineatus, a long distance migratory species commonly found in Paraná River basin drainages. Samples were obtained from six locations in the Upper and Middle Paraná River: Porto Primavera Reservoir, downstream of the Porto Primavera Reservoir, four tributaries of this reservoir (Pardo, Peixe, Verde and Aguapeí Rivers) and in the Iguaçu River, downstream of the Itaipu dam. High genetic diversity was observed in all samples, as expected for species with large population sizes and high migration rates. However, the influence of other factors, such as secondary contacts, fish passages and restocking were also suggested. In general, evidence of spatial population structuring was not found, even though there were two large dams in the study area. This could also be attributed to the brief period that has elapsed since the dams were built, the influence of migratory and reproductive patterns and the possible contributory effects of the fish passages. Furthermore, the absence of population structuring also corroborates existing information that emphasizes the importance of unimpeded tributaries for conserving migratory fish populations in fragmented watersheds.

Color patterns of the body are commonly used to distinguish and identify species of Trichomycterus. Therefore, variation in color pattern in a population can cause doubt concerning species identification. With the purpose to test the hypothesis of high variation in color pattern of Trichomycterus davisi (Haseman, 1911), 118 specimens were collected in a stream of a private Ecological Park in southern Brazil, of which 88 were used in the morphological analysis and 30 for DNA barcoding analysis. Three phenotypic classes were determined analyzing the distribution, size and shape of dark brown spots and blotches. The results of morphometric analysis indicate a tendency of association of those pigmentation patterns with the standard length, evidencing ontogenetic variation of color pattern in the species. The results of K2P intraspecific genetic distance (<0.72%), haplotypes network and Bayesian phylogenetic tree corroborate the existence of only one species with a high variable color pattern.

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The southern region of Brazil is characterized by high species diversity and endemism of freshwater fishes distributed across geographically isolated river basins. Microglanis cottoides has a widespread range across these river basins and occurs in sympatry with other endemic species of the genus (e.g. M. cibelae, M. eurystoma, and M. malabarbai). Herein we tested the monophyly of M. cottoides and presented for the first time information about the molecular phylogeny of species in the genus. The results suggest that M. cottoides currently forms a non-monophyletic group which includes populations endemic to the Uruguay River basin that are more closely related to M. malabarbai, and excludes M. cibelae, found to be nested within M. cottoides. Based on an integrative approach using morphological and molecular data, we propose M. cibelae as a junior synonym of M. cottoides, and the populations of the Uruguay River basin previously assigned to M. cottoides in fact belong to M. malabarbai. Our molecular phylogeny shows that M. cottoides is sister to M. parahybae, which is also a coastal species, and M. malabarbai is sister of M. garavelloi, both endemic to inland river basins. The time-calibrated phylogeny indicates that the separation between inland and the coastal clades occurred in the Tertiary period, and that the species within the coastal basins diverged in the Pliocene, which overlaps with the diversification times estimated for the two inland species as well. This pattern of diversification corroborates some previous studies with other fishes from the same region.

Specimens of Pimelodellacaptured in the Miranda River, Pantanal of Mato Grosso do Sul State, present morphological features that could indicate at least four species. Therefore, karyotype analysis and molecular biology provided evidence that they were only two species, one showing 2n = 46, and the other, 2n = 52 chromosomes, with only 18% genetic similarity. The morphological analysis evidenced that the dorsal filament is a male characteristic and that the upper lobe of the caudal fin was variable and might or might not be elongated in both species. With respect to morphometric characters, the formation of two groups was evident, but with a small overlap of specimens between them. Among the species with filaments on the dorsal fin observed in the Pantanal, the one with the lesser length of adipose fin base is P. griffini, which corresponds to that with 2n = 46 chromosomes, whereas the species P. taenioptera has 2n = 52 chromosomes. Thus, the accurate detection of these cryptic taxonomic units was only possible with the use of various analysis techniques. Furthermore, it is worth noting that the identification of cryptic species is important for obtaining correct estimates of fish diversity in the Pantanal

Gymnogeophagus setequedas is a rare and rheophilic species of tribe Geophagini, considered endangered in Brazilian red lists. Its previously known geographical distribution range was the Paraná River basin, in Paraguay, and a tributary of the Itaipu Reservoir in Brazil. Since its description no specimens have been collected in the original known distribution area. However, recent records of G. setequedas in the lower Iguaçu River, in a region considered highly endemic for the ichthyofauna, extended the known geographical distribution and may represent one of the last remnants of the species. The aim of this study was to estimate the genetic diversity and population structure of G. setequedas, using microsatellite markers and mitochondrial haplotypes, in order to test the hypothesis of low genetic diversity in this restricted population. Muscular tissue samples of 86 specimens were obtained from nine locations in the Lower Iguaçu River basin, between upstream of the Iguaçu Falls and downstream of the Salto Caxias Reservoir. Seven microsatellites loci were examined and a total of 120 different alleles were obtained. The number of alleles per locus (NA) was 17.429, effective alleles (NE) 6.644, expected heterozygosity (HE) 0.675, observed (HO) heterozygosity 0.592, and inbreeding coefficient (FIS) 0.128. Twelve haplotypes in the D-Loop region were revealed, with values of h (0.7642) and π (0.00729), suggesting a large and stable population with a long evolutionary history. Thus, both molecular markers revealed high levels of genetic diversity and indicated the occurrence of a single G. setequedas population distributed along a stretch of approximately 200 km. The pattern of mismatch distribution was multimodal, which is usually ascribed to populations in demographic equilibrium. Nevertheless, the construction of a new hydroelectric power plant, already underway between the Salto Caxias Reservoir and Iguaçu Falls, could fragment this population, causing loss of genetic diversity and population decline, and for this reason it is necessary to maintain the Iguaçu River tributaries and downstream area from the Lower Iguaçu Reservoir free of additional dams, to guarantee the survival of this species.

A new species of aeglid crab, Aegla okora n. sp., is described. This species was found in the Iguaçu River basin in Paraná state, southern Brazil. Aegla okora n. sp. was discriminated based on morphological and molecular data (mitochondrial COI). Morphologically, the new species differs from congeners of the same river basin by the presence of a trapezoidal areola and the ventromesial border of the ischium having three tubercles, besides other exclusive additional morphological characteristics. Molecular results demonstrated that there is no overlap between the intraspecific distances of Aegla okora n. sp. and the interspecific distance of other species of Aegla added to the analysis, confirming the separation of species and increasing the known diversity of the Iguaçu River basin.

The lack of knowledge on the distribution and taxonomy of ichthyofauna from coastal Atlantic Rainforest of Santa Catarina state, Brazil, is noteworthy. This study presents a rapid but comprehensive survey of fish species from the coastal hydrographic regions of Santa Catarina. The samples were conducted in October 2012, in 19 sampling sites of five hydrographic regions, using sieves, seine nets, and throw nets. A total of 1,878 individuals belonging to 51 species distributed in 16 families are reported; four freshwater fish species represent distribution novelties for the region. The families Characidae and Loricariidae were predominant, mainly due to the abundance of Astyanax sp., Mimagoniates microlepis, Epactionotus itaimbezinho, and Pareiorhaphis stomias. Therefore, this study provides important contributions to the knowledge of the freshwater fishes from the studied area.