Horácio F. Júlio

Fish diversity in the upper Paraná River basin: habitats, fisheries, management and conservation

The Paraná River is the second longest river in South America and the tenth largest river in the world in water discharge. The upper stretches are characterized by high human occupation and intense anthropogenic activities, and few areas are still in pristine conditions. Despite this, fish diversity is remarkably high in the upper Paraná River basin, and the existence of different habitats greatly influences fish biodiversity. Although most species are sedentary, migratory species are considered the most important, since they have historically sustained commercial and recreational fisheries. Recently, stocks of migratory species have diminished in many rivers due to overfishing and habitat modifications caused by dams. Impoundments have a long history in the basin and constitute the main source of impacts for both sedentary and migratory fish species. Government agencies have implemented management actions to mitigate the effects of damming on fish populations, which included fish stocking (using native and non-native species), the construction of transposition mechanisms and fishery control. However, their efficacy for conservation has been severely questioned and, in many instances, these actions have produced negative outcomes to biodiversity. The lack of studies and monitoring programs contributed to the uncritical adoption of some dubious management actions. Inevitably, management plans directed to conserve fish biodiversity in the basin need urgent revision.

Food spectrum and trophic structure of the ichthyofauna of Corumbá reservoir, Paraná river Basin, Brazil

In this paper we evaluate plasticity of fish concerning diet. We expect that sampling over a large temporal and spatial scale, including environmental changes such as impoundments, will allow us to cover most of the diet plasticity. We also evaluate the efficacy of ordination method in discriminating trophic groups based on fish species diet. Data were obtained from 17 sampling stations sampled monthly from March/96 to February/99 in the Corumba river drainage, before and after the formation of the Corumba reservoir. Diet was determined analysing 9,177 stomach contents from 64 fish species. Trophic categories were discriminated by a non-hierarchic grouping analysis named k-means, applied to diet data. Most of the species presented great trophic plasticity, eating a great variety of food items. Resources availability, estimated from all fish stomach contents, was similar among environments, except in creeks, where it varied more with a large importance of terrestrial insects. K-means present satisfactory results, identifying nine trophic groups (detritivores, herbivore-piscivores, insectivore-herbivores, omnivores, invertivores, aquatic insectivores, piscivore-insectivores, piscivores and herbivores). Neste estudo avaliamos a plasticidade trofica em peixes. Nos esperamos que amostras obtidas com uma ampla escala temporal e espacial, incluindo mudancas ambientais como represamentos, nos permita cobrir a maior parte desta plasticidade. Foi avaliada tambem a eficiencia do metodo de ordenacao em discriminar os grupos troficos baseado na dieta das especies. As amostragens foram realizadas mensalmente de marco/96 a fevereiro/99 em 17 estacoes de coleta na bacia do rio Corumba antes e apos a formacao do reservatorio de Corumba. Foram analisados 9177 conteudos estomacais, pertencentes a 64 especies. As categorias troficas foram discriminadas atraves de uma analise de agrupamento nao hierarquica denominada K-means aplicada aos dados de dieta. A maioria das especies apresentou elevada plasticidade trofica, consumindo uma grande variedade de itens alimentares. A disponibilidade dos recursos alimentares, estimada atraves de todos os conteudos estomacais, foi similar entre os ambientes a excecao dos riachos, onde ocorreu maior heterogeneidade e os insetos terrestres tiveram grande importância. A analise K-means revelou resultados satisfatorios, identificando nove grupos troficos (detritivoros, herbivoro-piscivoros, insetivoro-herbivoros, onivoros, invertivoros, insetivoros aquaticos, piscivoro-insetivoros, piscivoros e herbivoros).

Identification of Astyanax altiparanae (Teleostei, Characidae) in the Iguaçu River, Brazil, based on mitochondrial DNA and RAPD markers

Astyanax fishes are among the most important food-web components of South America rivers. In the Iguacu River basin, the Astyanax genus is represented mainly by endemic species. For millions of years, that hydrographic basin has been geographically isolated from the Parana River basin by the Iguacu Falls. Recently, a species from the Upper Parana River basin identified as Astyanax bimaculatus was revised and described as a new species named Astyanax altiparanae Garutti & Britski, 2000. Fauna endemism and geographic isolation triggered interest in investigations to evaluate the identification and genetic relatedness among two A. altiparanae populations from the Upper Parana River basin and the population identified as A. bimaculatus in the Iguacu River, upstream from the Iguacu Falls. Mitochondrial DNA sequences and RAPD markers revealed high genetic diversity within each population, as well as low genetic distance, high gene flow, and high mitochondrial DNA similarity among all three populations. In conjunction with morphological similarities, these results demonstrated that the population presently known as Astyanax bimaculatus in the Iguacu River should actually be stated as Astyanax altiparanae. Furthermore, it could be inferred that the A. altiparanae population is not endemic and most likely it was recently introduced in the Iguacu River basin, maintaining the ancestral genetic identity.

Colonização ictiofaunística do Reservatório de Itaipu e áreas adjacentes

Samples were taken from November 1983 to October 1989 in sites along the main body of the Itaipu reservoir and its area of influence to evaluate the impacts of this reservoir on ichthyofauna and to provide information about the colonization process in the dammed area. The ichthyofaunistic similarity between the sites was analysed during the studied period. Spatial and temporal variations of the ichthyofaunistic diversity were also done, using Shannon-Winer Index of Diversity, eveness and species richness, comparing the results with those obtained before the damming. After Itaipu Reservoir formation, it was observed significative alteration in specific abundance and ichthyofauna structure of the Parana River, with an increase in species number in ali tributaries of the reservoir, and a high replacement in species. Diversity and species richness were higher in the dammed stretch of the Parana river and in its tributaries of the left side after the Itaipu reservoir formation. Among the sampled sites, the highest values of the diversity index were registered in Parana River upstream and downstream the reservoir, Iguatemi river and Arroio Guacu. Based on information of similarity in species composition and abundance in the sampled area, five site groups could be identified.

Molecular biogeography of the Neotropical fish Hoplias malabaricus (Erythrinidae:Characiformes) in the Iguaçu, Tibagi, and Paraná Rivers

Hoplias malabaricus, the common trahira, extended its range into the Iguacu River sometime in the last decades. To determine levels of genetic differentiation in neighboring basins of this nominal taxon, as well as to unveil the source of the invading population, we analyzed patterns of similarity of RAPD-PCR genomic markers of samples from Parana, Iguacu and Tibagi Rivers. The high genetic diversity of samples from the Parana and Tibagi Rivers suggested strong population structuring or even the occurrence of undescribed species. All alleles of the sample from the headwaters of Tibagi River were present in the sample from the Iguacu River, which suggests that the former population or another population with similar genetic makeup, may be the source of the trahiras of the Iguacu River.

Erratum to: Invasibility of reservoirs in the Paraná Basin, Brazil, to Cichla kelberi Kullander and Ferreira, 2006

The invasion process comprises not only the characteristics of nonindigenous species but also the attributes of the invaded environment which make it susceptible to the establishment of nonindigenous species. Habitat attributes operate like filters in determining the establishment of introduced species and the invasibility of a region. In the Upper Paraná River Basin, Brazil, the practice of introducing species was quite common and frequently carried out by hydroelectric companies. The target species of the present study, the peacock-bass Cichla kelberi, is native to the Amazon Basin. This species was introduced into several reservoirs of the Upper Paraná River Basin and is dispersing rapidly throughout the system. This study shows which characteristics of the reservoirs facilitate their invasibility after testing for the effect of propagule pressure. We conclude that a set of abiotic factors favors the invasibility of these reservoirs. To be more precise, the largest, deepest, most transparent and warmest reservoirs are the most likely to be colonized by Cichla kelberi. It is possible that other environments with similar characteristics to these reservoirs, such as the lagoons from the Upper Paraná River Basin floodplain, can also be colonized by Cichla kelberi.

Chromosomal polymorphism and speciation in Laetacara cf. dorsigera (Teleostei, Perciformes, Cichlidae) from the river Paraná PR Brazil

Abstract Four sympatric and syntopic karyotype forms of Laetacara cf. dorsigera, centric fusion-originated were analyzed. Specimens with 2n=46, 2n=45, 2n=44 and 2n=43 chromosomes and differences with regard to the number of metacentric chromosomes, inversely proportional to their diploid number, were reported. Karyotypic formulae of the four cytotypes were: cytotype A=2M + 44A; cytotype B=3M + 42A; cytotype C=4M + 40A and cytotype D=5M + 38A and fundamental number constant (NF=48). Two centric fusion events are suggested: a) Robertsonian trans-location, which originated the first and second metacentric chromosomal pairs; b) isochromosome formed by the fusion of acrocentric homologous chromosomes in cytotypes with odd chromosomes. Genetic balance in the four karyotype forms of Laetacara cf. dorsigera seemed to have been determinant to their reproductive isolation. The presence of individuals with different karyotypic structures living in sympatry and syntopy and the absence of “intermediate individuals” (recombinants), that would have been expected in a panmitic population, permit one to conclude that probably form 4 cryptic species exist in the population.

Effects of the interannual variations in the flood pulse mediated by hypoxia tolerance: the case of the fish assemblages in the upper Paraná River floodplain

The effects of the duration of the floods on abiotic variables and attributes of species tolerant and intolerant to hypoxia (STH and SIH respectively) were evaluated in rivers and lakes of the upper Parana River. Fish were sampled once a year, in six sampling stations, during the high water period from 2000 to 2003. There were overall reductions in dissolved oxygen levels and increases in transparency of water in lakes in years of moderate floods. The duration of floods influenced species differentially based on their tolerance to hypoxia: in moderate floods, richness of STH increased and numerical abundance and biomass of SIH reduced significantly. Opposite relationships were detected between dissolved oxygen and the attributes of STH and SIH. Dissolved oxygen was the best predictor of variability of STH and SIH in years of moderate floods, whereas water transparency predicted significant amounts of STH in years of short floods. Being positively affected by dissolved oxygen reductions, STH seem to take advantages in persisting in seasonally harsh lentic habitats. The incorporation of abiotic data as well the differential tolerance of species to hypoxia would improve further investigations of the effects of interannual variations in the flood pulse on tropical fish assemblages