Dirceu Baumgartner

Fish, Salto Osório Reservoir, Iguaçu River basin, Paraná State, Brazil

The Iguacu River is a large tributary of the Parana River, with a highly endemic ichthyofauna due to the geographic isolation imposed by the Iguacu falls, located near its mouth. Fish were collected monthly in four sampling stations along the Salto Osorio Reservoir, from July 2003 to June 2005, using gill nets, casting nets, and long lines. Considering the entire period, 41 fish species were colleted, which belong to six Orders, 17 Families, and 27 Genera. From these, 24 species are considered endemic. Comparisons with other surveys conducted in the Iguacu River are provided, in addition to comments on the fish endemism, even within the basin.

Ichthyofauna of streams from the lower Iguaçu River basin, Paraná State, Brazil

The drainages of the Iguacu River basin, as well as the main channel of the river, have peculiar characteristics resulting from geomorphological processes in this area, including the formation of the Iguacu River Falls. This slope in the lower portion of the basin is a biogeographical barrier to many organisms. In this study was inventoried the fish fauna of streams of the lower Iguacu River basin, evaluating possible differences in the species composition upstream and downstream of this biogeographical barrier. Sampling were conducted between 2004 and 2013, in five streams, three upstream and two downstream of the Iguacu River Falls, using electrofishing. The nMDS analysis was run to investigate possible groupings of similar fauna between the streams sampled. The scores of this test were tested as to the significance of groupings with the Hotelling T2 test. The indicator value method (IndVal) was used to detect the distribution of species among the groups of the streams upstream and downstream of the Iguacu River Falls. We collected 18,908 individuals of six orders, 11 families, and 40 species. Siluriformes and Characiformes had the highest species richness; Cyprinodontiformes presented the highest abundance. Considering the species recorded, 21 are considered natives to the Iguacu River basin, including 15 endemic, wich were found only in streams upstream of the falls. Additional 18 species were verified only in the streams downstream of such barrier. Four species were common to both stretches. The axis 1 of the nMDS separated two groups: streams upstream (S1, S2 and S3) and streams downstream of the Iguacu River Falls (S4 and S5). The indicator species analysis also indicated a distinction between the groups of streams, that were significantly different (Hotellings T2 = 234.36, p ˂ 0.0001). The number of endemic species in the streams upstream of the Falls (15 spp.) evidences a significant effect of isolation promoted by the Iguacu River Falls, and confirms the role of this barrier in the vicariant processes and endemism typical of this basin. These results emphasize the importance of conserving these ecosystems, once the extinction of species in this region means the irreversible loss of them.

Is resource partitioning the key? The role of intra-interspecific variation in coexistence among five small endemic fish species (Characidae) in subtropical rivers

This study focused on intra and interspecific variations in the diet of small species in the Pelotas River, upper Uruguay River ecoregion. We tested the hypothesis that five small characids coexist via resource partitioning. Samplings were performed quarterly between August 2013 and May 2014 at 14 sites in the Pelotas River basin, using gillnets of different mesh sizes, seines, cast nets and electrofishing. In this study, the contents of 1,253 stomachs were analysed from Astyanax dissensus, A. paris, A. saguazu, A. xiru and Bryconamericus patriciae. The main food resources consumed were aquatic insects, leaves, seeds and detritus. There were significant seasonal intra and interspecific variations in the use of food resources by the five species. Permutational analysis of multivariate dispersions results indicated significant differences in individual intraspecific variability between the sampled periods, with the highest values found in November and February because of an increase in allochthonous resources (leaves and seeds). Besides this, significant differences in the proportions of consumption of allochthonous and autochthonous were observed. The trophic niche breadth was significantly different among the species, such that in August, the species had narrower niche breadths. In the other periods, the highest niche breadth values were due to an increase in the consumption of allochthonous items. Diet overlap was low (< 0.4) between 62% of the species pairs. The small characid species showed pronounced changes in resource use and intra and interspecific variations indicating resource partitioning. These factors appear to be essential in species interactions and for coexistence.