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This study provides an updated list of parasite species and their respective hosts in the upper Paraná River floodplain. The list of parasites is structured by phylum, class, order and family, followed by a record of each host species. A total of 315 taxa of parasites were reported, of which 201 were identified at the species level. These 201 species comprise 3 Flagellata, 3 Myxozoa, 50 Monogenea, 43 Digenea, 40 Cestoda, 41 Nematoda, 8 Acanthocephala, 6 Copepoda, 5 Branchiura and 2 Pentastomida, arranged in 84 host fish species. This work carried out in the floodplain of the upper Paraná River contributes to the listing of parasite species and host interactions of the local ichthyofauna. Little is known about these communities and its riches are underestimated due to the high density of fish found in this region, highlighting the importance of conducting studies on the local fauna.

Endoparasites that are trophically transmitted are closely intertwined and constrained by the structure of the food chain. Each fish species can be used as an intermediate or definitive host; thus, the position it occupies in the food web and the body size can be determining factors for the presence of parasites and their transmission. Considering that fish can be parasitized by larval and adult stage endoparasites and that they are exposed to a wide variety of parasite species, we used a helminth dataset from 70 fish species and tested whether the total parasite richness, larval and adult, of fish from the upper Paraná River floodplain can be explained by body size and trophic level. For the trophic level, we observed an increasing trend in the richness of larval parasites. Regarding the richness of adult parasites and the total richness, we observed an increase as a function of the body size of the host. The tropic position and body size of the fish were good predictors, indicating that the position of the host in the trophic chain can influence and determine its life cycle.

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The construction of dams causes several impacts on aquatic environments, altering the flow of rivers, environmental variables, and all biota present, including parasites. Little is known about how the parasitic community can be influenced in the long term by environmental changes. In this study, it was expected that the impacts caused by environmental disturbances will be directly reflected by the composition of the parasite populations. We evaluated the change in the structure of the Prochilodus lineatus endoparasite community between two periods sampled 15 years apart in the upper Paraná River floodplain. There was a significant difference in the weight–length relationship of P. lineatus between these periods and a total of 15 species of parasites were found: 11 species in Period 1 and nine species in Period 2 and five species occurred in both periods. The species richness and diversity were higher in Period 1, and we observed that the correlation of descriptors (richness, diversity and evenness) increased with fish length in this period. In both periods, digeneans numerically dominated the parasitic community, and we verified changes in the composition of parasites between periods. Both the host and the parasites were possibly affected by the environmental impacts resulting from the construction of dams over time, and it is noteworthy that complex life cycle parasites such as Digenea and Acanthocephala require intermediate hosts to complete their life cycle, and the population responds to fluctuations in the face of modified environments.

Aim The aim of this study was to present the description of new species of fish parasites in native and non-native hosts and the parasite interaction / host, available in studies for 37 years in the upper Paraná River floodplain. Methods The sampling described in this study is part of a scientometric methodology, in which specific query expressions were used, together with the database available in the Nupelia Sector Library, through Theses and Dissertations. Results A total of 44 species of parasites belonging to different groups were described for 27 species of fish of different orders. In these 37 years of studies, an increase 68% was observed in the number of parasite species, presenting a richness of 201 species in the floodplain, being: Monogenea, Digenea, Nematoda and Cestoda are the groups that present the largest records of species. More than 80 hosts have their parasite fauna registered and most studies are carried out with species of native hosts in the floodplain, being Prochilodus lineatus the host with the highest number of records. Conclusions Parasitological studies are an important scientific tool for understanding the dynamics of ecological interactions in the natural environment, and knowledge of this diversity of organisms is continuous and necessary, and the results of the monitoring carried out in the floodplain during the last 37 years only reinforce this with a constant increase in the description of new species and new records of parasite-host interactions. In times of constant environmental loss and habitat fragmentation, it is of utmost importance to care for and preserve floodplains to maintain biodiversity.

In the present study, we investigated the possible toxic effects of phenol on two bioindicators: the fish Astyanax bifasciatus (Characiformes; Characidae) and the crustacean Daphnia magna (Cladocera; Daphnidae). We performed bioassays with A. bifasciatus (96 h and 15 days of exposure) and D. magna (48 and 96 h of exposure). The bioindicator organisms were exposed to the following concentrations of phenol: 0.003 mg L-1 , 0.01 mg L-1 , 0.03 mg L-1 , 0.06 mg L-1 , and 0.1 mg L-1 ; and the control group was maintained in clear water. We assessed the rate of micronuclei in erythrocytes of fish and evaluated the immobility of D. magna at each concentration of the contaminant. For fish, the 15-day exposure revealed a significant difference between the tested groups (p = 0.0002), showing a tendency for micronuclei to increase at the highest concentrations. For the D. magna test, 96-hour toxicity was evident at all tested concentrations (p < 0.05). A better response of these organisms was observed during the longer exposure period, emphasizing the concern on the long-term effects of phenol. Effects on the lowest concentration of phenol tested (0.003 mg L-1) were also observed, and this concentration is permitted by the Brazilian Legislation for Class II waters, demonstrating that the longer time of exposure to phenol can cause damage to the biota.

The objective of this research was to validate the colonization process on natural and artificial substrates by benthic invertebrates in a tropical stream in South Brazil. The samples were performed in July and August-2012, and 32 samplers were used, being 16 natural and 16 artificial substrates. In each sample, two replicas were taken for each substrate at the 2th, 4th, 7th, 14th, 21th 28th, 35th and 42th days of colonization. The organisms were identified to the lowest possible taxonomic level. In both substrates 3,070 benthic invertebrates were detected, of which 1,753 individuals were collected on the natural substrate, and 1,317 on the artificial substrate. From the identified taxa 8.5% were not dominant (Anacroneuria, Orthocladiinae, Tupiara, Smicridea, Baetodes, Tupiperla, Macrogynoplax, Gripopteryx, Cylloepus, Macrelmis, Microcylloepus, Hetaerina, Argia, Coryphaeschna, Atopsyche, Pomacea, Corydalus, Leptohyphes and Eccoptura), and 31.5% were dominant (Tanypodinae, Chironominae, and Paragripopteryx). The genus Simulium was very common, dominant and abundant, representing 65% of the collected individuals. No significant difference was found in the abundance and species composition between artificial and natural substrates. On the natural substrate, the higher colonization index was at the 35th day with 459 individuals, and the lowest was at the 14th day, with 87. On the artificial substrate the highest index was at the 42th day with 337 individuals, and the lowest was at the 4th day, with 85. Both natural and artificial substrates are efficient in characterizing the benthic community. In the evaluation of the ecological succession, it was not possible to observe a pattern that described the process, since the composition was nearly constant throughout the study period.