The functional traits of host fish can act as good predictors for parasite composition in a neotropical floodplain.

Parasite diversity can be influenced by the interaction of environmental factors and host traits, but understanding which traits can be decisive for the establishment of the parasite may provide subsidies for a better understanding of the host-parasite relationship. In this study, we investigated whether functional traits, diet, and host phylogeny can predict the similarity of the endoparasite composition of a fish assemblage in a Brazilian floodplain. Of the three evaluated components, the host's diet was the factor that showed the greatest influence on the composition and similarity of endoparasites, demonstrating the highest value of the explanation. The functional traits and phylogeny, despite presenting significant values (unique effect and global effect), showed low explainability in the composition of the endoparasites. When analyzing the joint effects, all components showed significant influence. Hosts that live in the same environment that are phylogenetically related and have a similar ecology have a certain degree of homogeneity in their parasite assemblages and, because they are endoparasites (which are acquired trophically along the chain), diet is the main driver of parasite richness and similarity. Overall, host traits can be one of the main determinants of parasite composition, so studies that address the functional traits of the host provide a representation of local diversity and define the possible patterns of these parasite communities.

Essential and toxic elements in juvenile migratory commercial fish species in the Paraná River alluvial valley (South America): an approach for aquatic environmental monitoring.

The Paraná River is the sixth largest in the world, and the lower section of the river is one of the largest and most productive floodplain wetlands in South America. The alluvial plain is an important habitat for nursery and feeding areas for commercial fish; however, it has been heavily anthropized due to industries, agricultural activities, and the growth and expansion of metropolitan areas. The aim of this study was to determine element accumulation (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) in young-of-the-year fish muscle from a floodplain lagoon of the lower Paraná River (Argentina) during summer and winter seasons, in relation with abiotic matrices (water and sediment). Four commercial fish species were assessed: sábalo (Prochilodus lineatus), boga (Megaleporinus obtusidens), dorado (Salminus brasiliensis), and pirapitá (Brycon orbignyanus). The concentrations of eight elements were detected by quadrupole inductively coupled plasma mass spectrometry. In water samples, Cd, Cr, Mn, Fe, and Zn levels were under the permissible limits for aquatic biota protection in both seasons, except for Pb (> 1 µg L-1) and Cu (> 2 µg L-1). In sediment, the average concentrations of all elements were under the limits set by national and international regulatory authorities. Differences in elemental concentrations between species and seasons were found. In general, the levels of elements in water were higher in summer than in winter, while in sediment, the lowest concentrations of elements were detected during the summer. The order of element concentration in fish muscle was Cd (0.01-0.04 µg g-1) < As (0.02-0.16 µg g-1) < Pb (0.03-0.23 µg g-1) < Mn (0.77-4.32 µg g-1) < Cu (1.01-4.07 µg g-1) < Cr (1.09-4.30 µg g-1) < Zn (15.8-31.7 µg g -1) < Fe (12.6-49.7 µg g-1). The accumulation assessment showed that the four fish species significantly accumulate Cr, Cu and Zn, and As and Zn from water and sediment, respectively. The correlation analysis showed a relationship between fish size and As, Cr, Cu, Fe, Mn, and Zn concentrations. Similarly, the highest values of element concentrations in muscle were detected during the summer when the fishes are early juveniles. The level of As, Cd, and Pb detected in B. orbignyanus, M. obtusidens, and P. lineatus juveniles suggested that these species had the potential to be used as biomarkers for assessing accumulation of toxic elements in the environment. Also, this study reveals that the accumulation patterns differ between size and fish species, which should be a considered insight at the moment of selecting a bioindicator to monitor pollution in the ecosystem.

Species diversity and phylogeography of the Australoheros autrani group (Teleostei, Cichlidae) in eastern Brazil.

Cichlid fishes are an important model system in evolutionary biology, primarily because of their exceptional diversity. However, while some cichlid assemblages, such as the ones of the African Great Lakes, have received considerable attention, others are not well studied, including many riverine species. Here, we focus on the Australoheros autrani species group and first report a new record of Australoheros in the upper Paranaíba River drainage, extending the known distribution range of this genus. Through Bayesian inference and maximum likelihood phylogenetic analyses of the mitochondrial cytochrome b gene of these specimens as well as available sequences, we assigned the newly discovered population to Australoheros barbosae. We corroborate the monophyly of the A. autrani species group and the presence of three species in the upper/middle Paraíba do Sul River basin as well as molecular diagnostic characters for each. Finally, we provide evidence for a recent expansion of A. barbosae. Supplementary Information: The online version contains supplementary material available at 10.1007/s10228-022-00888-9.

Factors affecting the transferability of bioindicators based on stream fish assemblages.

The development of multimetric indices (MMIs) to measure the biotic condition of aquatic habitats is based on metrics derived from biological assemblages. Considering fish assemblages, the inconsistencies in metrics responses outside of the places where they were developed limit MMI transferability and applicability to other locations, requiring local calibration. The factors behind the low transferability of these MMIs are still poorly understood. We investigated how environmental dissimilarity and spatial distance influence the transferability of metrics generated from local stream fish assemblages to other regions. We also tested whether functional and taxonomic metrics respond differently to the spatial distance. We used data from 239 fish assemblages from streams distributed across a Brazilian, the upper Parana basin and characterized each site according to the level of anthropogenic disturbance at the landscape scale using an Anthropogenic Pressure Index (API). We divided the upper Parana basin into sub-basins and used two of them to create template response models of the metrics in relation to the API. We used these response models to predict the responses outside the template sub-basins. Our response variable representing a metric of transferability was the absolute difference between metric's predicted and observed value for each site (prediction error). We thus modeled the prediction error in relation to the predictor variables that were i) the environmental dissimilarity between each site with the average of the sites from template sub-basins (climatic, topographic and soil type variables) and ii) the spatial distance (overland and watercourse distance) between each site and the center of the template sub-basin. We found that errors in metric predictions were associated with both environmental dissimilarity and spatial distance. Furthermore, functional and taxonomic metrics responded equally to spatial distance. These results indicate the need for local calibration of metrics when developing MMIs, especially if the protocols already available come from distant and environmentally dissimilar places.

Plastic ingestion by carnivore fish in a neotropical floodplain: seasonal and interspecific variations.

Some studies have shown that freshwater ecosystems are polluted in a similar proportion to marine ecosystems; however, there are many gaps to be filled in this topic. Here, we investigated whether plastics were consumed by carnivore fishes in a Neotropical floodplain and whether it was connected to seasonality (dry and wet seasons). We also evaluated the association between each type of plastic and the fish species. We analyzed the gastrointestinal contents of 23 species and assessed the occurrence and number of plastic particles. Plastics were obtained through chemical digestion and the spectrum of each sample, using a FT-IR imaging microscope. We performed a correspondence analysis (CA) with plastic data to assess the relationship between each type of plastic and the fish species. We also performed linear regression models to assess the relationships of occurrence and number of plastics ingested with seasonality. Nine species had plastics in their gastrointestinal contents, and they were identified as polyvinyl alcohol (PVA), polyamide (PA), polyethylene (PE), polystyrene (PS), and polypropylene (PP). The number of plastics had a positive relationship with the wet season, while the occurrence did not show a significant relationship with any season. These results are particularly important when considering the socioeconomic relevance and the ecological importance of this trophic guild.

Infection pattern of Echinorhynchus salobrensis (Acanthocephala) in congeneric species of piranha from a Neotropical floodplain region.

Acanthocephalans are obligate endoparasites characterised by the presence of a proboscis with hooks, which are used to adhere and perforate the intestinal wall of their hosts. Individuals of Echinorhynchus salobrensis Machado Filho, 1948 have been reported parasitising the piranhas Serrasalmus maculatus Kner and Serrasalmus marginatus Valenciennes in the upper Paraná River floodplain. Serrasalmus marginatus is considered non-native at this site, and its establishment occurred after the closure of the Itaipu Hydroelectric, which flooded a natural geographic barrier that separated two ecoregions in the Paraná River. Since they are phylogenetically close and have similar biological and ecological characteristics competition for resources caused the non-native species to become dominant over the native one. Considering the specificity of species of Echinorhynchus Zoega, 1776 in serrasalmids, we evaluated the distribution of E. salobrensis along the gastrointestinal tract of S. maculatus and S. marginatus from the upper Paraná River floodplain. All parasites indices of E. salobrensis were higher in the invasive host S. marginatus when compared to the native S. maculatus. There were no significant interaction effects between host species and sex, and host species and/or sex in the presence of the parasite. When we evaluated the effect of E. salobrensis parasitism on the different gut regions and accessory organs, total abundance was significant in the stomach and caecum organs, and in the first and second regions of the intestine. None of the analytical approaches tested showed an effect of the sex of the host or the sex of the parasite on the presence and abundance of the parasite in the gastrointestinal tract. Studies on acanthocephalan parasitism in fish in Brazil focus on fish farm. The fact that two species of selvage carnivorous fish present high rates of acanthocephalan parasitism, added to the fact that most studies with this group are on farmed fish fed with feed, only emphasise the need for continuity in studies of acanthocephalans in the parasitology of aquatic organisms.

Fishers' knowledge on a large floodplain river in South America. Contributions for sustainable management of inland fisheries.

This study presents a comparison between fishers' knowledge and fiscal records about the structure of inland fisheries in the Paraná River (Argentina). First of all, we characterized the fishing population according to the main demographic and economic indicators, identifying two different fishing areas: the northern and southern sections in the lower La Plata basin. Secondly, we carried out a comparative analysis of fiscal fishery records (from two commercial sets: 1930-1984 and 2011-2019) and local fishers' knowledge on inland commercial fisheries (frequency of occurrence and abundance). Finally, we contrasted current fishing regulations (allowed meshes and boats, fishing prohibitions, exports) to fishers' effective practices. The study area included 52 sites located along the floodplain of the middle and lower sections of the Paraná River, in the province of Santa Fe. Socioeconomic analyses identified two different groups of fishers throughout the river corridor. Results showed that fishers have detailed knowledge on nomenclature, ecology, reproductive strategy, habitat distribution, and usefulness of commercial fish species. By contrasting fishers' knowledge with fiscal records, we found similar and complementary information about the changes in abundance and frequency of occurrence in fisheries. These results highlight the need of including local knowledge as an outstanding source of information for well-planned management of fishing programs and sustainable policies. Supplementary Information: The online version contains supplementary material available at 10.1007/s11160-022-09722-x.

Symmetries and asymmetries in the topological roles of piscivorous fishes between occurrence networks and food webs.

Ecological networks represent the architecture over which diversity is assembled. The compartmentalization of trophic links and the spatial aggregation of species determine ecosystem dynamics and stability. Species traits such as body size or those related to dispersal ability or environmental and trophic niche may determine the role of a species in different ecological networks such as food webs and occurrence networks. However, the empirical analysis of these connections and their determinants were seldom considered. Our study focused on 16 species of piscivorous fishes from 27 water bodies of the Paraná River floodplain, which were surveyed between 4 and 20 times over 5 years. Occurrence networks and food webs were built from abundance of species by site and preys by gut content. Using null models and methods for weighted bipartite networks, we evaluated the compartmentalization in both kinds of networks. The topological roles of species in each network along four hydro-climatic conditions were calculated, based on their membership in a module standardized within module connectivity 'z' and between module connectivity 'c' and related to species body size and 30 eco-morphological variables. A significant modular organization in feeding links and species occurrences was detected. While species of larger body size seem to have a main role connecting modules in food webs, the smaller size species foster the connection among spatial aggregations. However, body size was not the main determinant of intra module connectivity. Morphologies associated with linear races (fusiform body) and manoeuvrability (orbicular body) and predation behaviours were consistently related to intra and inter-module connectivity in food webs and occurrence networks. Our results support the modular organization of food webs and occurrence networks of the main consumers of the Paraná River floodplain and the trait-related interrelationship among these networks. Furthermore, the dynamic nature of the trait-role association may foster the stable modular structure observed at higher levels. The recognition of the connecting role of the species in the different networks will improve the understanding of their importance in the functioning of ecosystems, thus enhancing the knowledge of the mechanisms shaping biodiversity.

Las redes ecológicas representan la arquitectura sobre la cual se ensambla la biodiversidad. La compartimentalización de las interacciones tróficas y las agregaciones espaciales de las especies determinan la dinámica y estabilidad de los ecosistemas. Los rasgos morfológicos como el tamaño corporal o aquellos relacionados con la capacidad de dispersión y la configuración del nicho (trófico y espacial) pueden determinar el rol de las especies en diferentes redes ecológicas, como las tramas tróficas y las redes de ocurrencia. Sin embargo, el análisis empírico de estas conexiones y sus determinantes fueron escasamente estudiados. Nuestro trabajo se centró en 16 especies de peces piscívoros colectados en 27 cuerpos de agua de la llanura aluvial del Río Paraná, los cuales fueron muestreados entre 4 y 20 veces durante 5 años. Las redes de ocurrencia y las tramas tróficas fueron construidas con la información de la abundancia de los depredadores por sitios y la abundancia de las presas en los contenidos estomacales, respectivamente. Usando modelos nulos y métodos para redes bipartitas cuantitativas, evaluamos la compartimentalización en ambos tipos de redes. Los roles topológicos de cada especie se calcularon para cada red en cuatro situaciones hidro-climáticas diferentes, basándonos en sus conexiones dentro de su módulo de residencia (valor z) y por fuera de su módulo de residencia (valor c). Posteriormente, relacionamos los roles topológicos con el tamaño corporal y con 30 variables ecomorfológicas. Detectamos que las tramas tróficas y las redes espaciales presentan una estructura modular significativa. Los depredadores de gran tamaño corporal tuvieron un rol central en la conexión modular en las tramas tróficas, mientras que los depredadores pequeños permitieron la conexión entre las agregaciones espaciales. Sin embargo, el tamaño corporal no fue un determinante central en el rol de conexión intra-modular. La morfología asociada con la natación lineal (cuerpo fusiforme), la maniobrabilidad (cuerpo orbicular) y el comportamiento de cacería se relacionaron de manera consistente con los roles topológicos en las tramas tróficas y las redes de ocurrencia. Nuestros resultados sostienen que tanto las tramas tróficas como las redes de ocurrencia de los principales consumidores del Río Paraná medio presentan una organización modular y que los roles topológicos en ambas redes se encuentran interrelacionadas por los rasgos de las especies. Además, la naturaleza dinámica de la relación entre los rasgos y los roles topológicos puede permitir una estructura modular estable a niveles de organización mayores. El reconocimiento de los roles topológicos de las especies en diferentes redes ecológicas puede mejorar nuestro entendimiento de la importancia del funcionamiento ecosistémico, potenciando nuestro conocimiento sobre los mecanismos que sostienen a la biodiversidad.

The use of an integrative approach to improve accuracy of species identification and detection of new species in studies of stream fish diversity.

In this study, we made an inventory of the stream and headwater ichthyofauna of the left bank of the Itaipu Dam Reservoir, located in the lower part of the Upper Paraná River basin, using an integrative approach of molecular and morphological data. The area is located in the western portion of the Paraná state in Brazil, in an area of about 8,000 km2 highly impacted by deforestation and intensive agriculture. For taxonomic identification of species, we used an identification key combined with the DNA barcoding approach. We found 48 species belonging to six orders, 13 families, and 37 genera. The Siluriformes and Characiformes were the most representative orders (75%) and the Characidae was the most representative family (20.8%). Nine species prevailed in this region, making up to 86% of all specimens collected. The integrative approach proved to be useful by allowing the unambiguous identification of all species, including those cases in which morphological characters were not conclusive for species identification, cases of cryptic species, and species with high morphological plasticity. In addition, the integrative approach highlighted six to 13 new putative species depending on the approach considered. Our study provides a relevant contribution to the knowledge of fish diversity in a poorly studied area of the Paraná River basin. We showed that the use of an integrative approach in inventory studies improves species identification and the discovery of new, cryptic, and overlooked species, being a powerful and necessary tool to quantify biodiversity.

In situ exposure of amphibian larvae (Rhinella fernandezae) to assess water quality by means of oxidative stress biomarkers in water bodies with different anthropic influences.

In situ bioassays provide valuable information about the environment and offer more realistic results than usual laboratory experiments. The aim of this study was to evaluate the quality of water bodies from the lower Paraná River basin, the second most important in South America, through analysis of physiochemical parameters, metals and pesticides and in situ exposure of Rhinella fernandezae larvae to assess oxidative stress biomarkers. The sites were: S1(Morejón stream, reference); S2, S3(De la Cruz stream upstream and downstream, respectively) and S4(Arrecifes River). In all sites, dissolved oxygen was low, atrazine was detected and Cu was higher than the limit for aquatic life protection. According to the water quality index, S2, S3 and S4 presented bad water quality, while S1 good water quality. Larvae were exposed in situ for 96h in order to analyze: lipid peroxidation(TBARS) as oxidative damage, antioxidant enzymatic (catalase-CAT-, superoxide dismutase-SOD- and glutathione s-transferase-GST-) and non-enzymatic defenses (reduced glutathione-GSH-). Larvae exposed in the most impacted sites (S2, S3 and S4) presented oxidative stress since the levels of TBARS were around 2 times higher than in S1. Also, the other oxidative stress biomarkers were altered in larvae exposed at S2, S3 and S4. These results highlight the importance of analyzing oxidative stress biomarkers during in situ exposures since they are useful tools for documenting the extent of exposure at sublethal levels. The complex pollution of the water bodies affected the exposed larvae, which may jeopardize the native populations.

Three New Species of Cosmetocleithrum (Monogenea: Dactylogyridae) Gill Parasites of Trachelyopterus galeatus (Siluriformes: Auchenipteridae) in Southeastern Brazil.

PURPOSE: To describe three new species of Cosmetocleithrum in the gills of Trachelyopterus galeatus (Siluriformes, Auchenipteridae) from Aguapeí River, Upper Paraná River basin, São Paulo State, Brazil. METHODS: Fifty-three specimens of T. galeatus were captured in the mouth of the Aguapeí River from August 2013 to June 2014. Monogeneans were mounted unstained in Hoyer's and Gray and Wess's medium. RESULTS: Cosmetocleithrum spathulatum sp. n., Cosmetocleithrum baculum sp. n., and Cosmetocleithrum galeatum sp. n. differ from all known congeneric species mainly in the morphology of the accessory piece (i.e. spatulate-shaped, claviform, and a straight rod with hook-shaped distal portion, respectively). Also, the three new species share hooks with different sizes with hooks pairs 5 and 7 bigger than others and with an erect delicate point, inconspicuous thumb, longer shaft, and slender shank. CONCLUSIONS: To date, 18 species of Cosmetocleithrum were recognised parasitizing siluriforms in the Neotropical region. The present study expands the number to 21 species, however, despite this increase, the number of known taxa of monogeneans in neotropics is far from representing the ideal situation.

Quantification and composition analysis of plastic pollution in riverine beaches of the lower Paraná River, Argentina.

Plastic pollution and the numerous consequences it has on aquatic life have become a huge concern in recent years. While many studies have been conducted in marine environments, studies in freshwater ecosystems are scarce and insufficient. The Paraná River is the most important water course in the La Plata River basin and the fifth in the world with a mean annual discharge of 18,000 m3 per second. Currently available studies show the presence of plastic in river shores and fish gut, but more research should be carried out in order to know the extension and origin of plastic contamination. Therefore, the aim of this study was to quantify and characterize macro-, meso-, and microplastics found in the riverine beaches next to Rosario city, the most populated city standing by the lower Paraná River coast in Argentina. The results show that plastic pollution is ubiquitous, but the city shores are significantly more polluted than the wetland shore with a mean of 30,780 and 6375 microplastics per square meter respectively (p = 0.024). The food and beverage industry packaging combined were the most frequent macroplastics found. Also, 3 out of 4 meso- and microplastics were white/transparent, the color that is most likely to be ingested by fish and invertebrates. Finally, all micro- and mesoplastics found were secondary and, in the case of microplastics, they were mainly fibers (93.4%) which highlight its ecological relevance. As a whole, plastic contamination is a serious issue in the Rosario area, specially single-use plastics and short-lived products. The anthropic effect of the cities and how it contributes to plastic pollution are evident.

Long-term trends of fishery landings and target fish populations in the lower La Plata basin

The La Plata basin is the second largest basin of South America and has supported important river fisheries for more than a century. In this paper, we evaluate for the first time the historical trends of landings of 21 fish taxa and the recent population trends of 27 species of commercial fishes in the lower La Plata basin (Argentina). We compiled three kinds of data sets: Total fishery landings (between 1934 and 1986) and exports (1994‒2019), fisheries monitoring programs of Chaco and Santa Fe provinces in the Paraná River (2009‒2019), and surveys of fish populations in the Upper (Corrientes, 1993‒2020) and Middle (EBIPES, 2005‒2020) Paraná River. The analysis of the historical landings showed more species declining in the lower portion of the basin than in the upper basin. Regarding recent population trends, Pimelodus spp., Hoplias spp., Salminus brasiliensis, Luciopimelodus pati, and Ageneiosus spp. declined in more than one region, while Megaleporinus spp., Pterodoras granulosus, and Oxydoras kneri showed stable to positive trends, with the other species varying in their trends between regions. These tendencies could be associated to a combination of factors such as overfishing and environmental changes that would require an ecosystem approach for their adequate management.(AU)

La Cuenca del Plata es la segunda más grande de Sudamérica y ha soportado importantes pesquerías fluviales desde hace más de un siglo. En este trabajo, evaluamos por primera vez las tendencias históricas en los desembarques pesqueros de 21 taxones de peces y las tendencias poblacionales recientes de 27 especies de peces comerciales de la baja Cuenca del Plata (Argentina). Compilamos tres tipos de datos: desembarques pesqueros totales (1934‒1986) y exportaciones (1994‒2019), programas de monitoreo de pesca comercial de las provincias de Chaco y Santa Fe en el río Paraná (2009‒2019), y relevamientos de peces en el río Paraná Alto (Corrientes, 1993‒2020) y Medio (EBIPES, 2005‒2020). El análisis de los desembarques históricos mostró más disminuciones en la porción baja de la cuenca que en la porción alta. En cuanto a las tendencias poblacionales recientes, Pimelodus spp., Hoplias spp., Salminus brasiliensis, Luciopimelodus pati y Ageneiosus spp. declinaron en más de un sector, mientras que Megaleporinus spp., Pterodoras granulosus y Oxydoras kneri mostraron tendencias estables a positivas, con las otras especies variando en sus tendencias entre regiones. Estas tendencias podrían asociarse a una combinación de factores como la sobrepesca y los cambios ambientales que requerirían una aproximación ecosistémica para su adecuado manejo.(AU)

A new species of Phenacorhamdia Dahl 1961 (Siluriformes: Heptapteridae) from the Paranapanema River basin, southeastern Brazil.

A new species of Phenacorhamdia is described from Paranapanema River, Upper Paraná River basin, southeastern Brazil. The new species is distinguished from congeners by the combination of following characters 45-46 vertebrae; an entirely dark-brown body; nine pleural ribs; eight branched rays in upper lobe of caudal fin; seven branched rays in pectoral fin; 13 anal-fin rays with 9-10 branched; first basal radial inserted at the 13th vertebrae and eight branchiostegal rays.

First fossil of the Giant Armored Catfish Acanthicus (Siluriformes, Loricariidae) from the Late Miocene of Entre Ríos Province, Argentina.

Loricariidae is a very diverse lineage of Neotropical fishes, being the most speciose family of the order Siluriformes. However, the loricariid fossil record is still very sparse. The aim of the present contribution is to describe in detail several bones belonging to the loricariid genus Acanthicus coming from late Miocene beds located at the Paraná River cliffs, Entre Ríos province, Argentina. Fishes of the Acanthicus clade are currently restricted to the northern half of South America, being mainly distributed in the Orinoco and Amazonas basins, with a single genus reaching the Paraná-Plata basin. Acanthicus adds to the list of several taxa that are shared by the Miocene of Paraná, Amazonas and Orinoco basins, but that nowadays are absent in the former (e.g., Colossoma, Phractocephalus, and Brachyplatystoma), and are typical of large river channels. This report of Acanthicus supports a close affinity between freshwater faunas of the Paraná, Orinoco, and Amazonas basins. Miocene fossils of freshwater fishes recorded in Paraná beds shed light on the connections between ancient basins of South America and also indicate that several fish clades suffered regional extinctions during the late Neogene or the beginning of the Quaternary.

The Life Cycle of Heterophyes yacyretana n. sp. (Digenea, Heterophyidae), Parasitic in the Endemic Snail Aylacostoma chloroticum (Caenogastropoda, Thiaridae) in Argentina.

Here we describe a new heterophyid species, Heterophyes yacyretana n. sp., and resolve its life cycle experimentally. We found the prosobranch snail Aylacostoma chloroticum in Candelaria, Province of Misiones, Argentina (a sector of the High Paraná River affected by the Yacyretá Dam), naturally infected with opisthorchioid cercariae. These cercariae lacked pigmented eyespots as well as body pigment and possessed 7 pairs of penetration glands arranged in 2 lateral bands, together with 18 pairs of flame cells and a V-shaped excretory vesicle. We exposed specimens of 21 fish species to emerging cercariae and obtained metacercariae from the muscles of the caudal peduncle of 3 species of siluriform fish, and adults from chicks infected with experimentally obtained metacercariae from the albino variety of the bronce corydoras, Corydoras aeneus. The new species differs from other species in the genus by the number of sclerites on the genital sac, the distribution of the vitelline follicles, and the combination of the size relationship of the suckers and the genital sac with respect to the posterior extent of intestinal ceca. Heterophyes yacyretana is the first species of the genus reported from the Americas.

Yellow-eyed piranhas produce louder sounds than red-eyed piranhas in an invasive population of Serrasalmus marginatus.

Serrasalmus marginatus is a piranha species native from the lower Paraná River basin and has been invasive in the upper Paraná River basin since the 1980s. In piranhas, sounds of different species have different features. The aim of this study was to investigate if the sounds produced by this species could be used to distinguish two morphotypes: red- and yellow-eyed S. marginatus from the Araguari River (upper Paraná River basin). All the temporal and frequency features of the sounds were equivalent in both groups of eye colour; it corresponds to the species-specific signature described for S. marginatus. Nonetheless, the amplitude features were all statistically different between red- and yellow-eyed piranhas. Yellow-eyed specimens produced louder sounds. In different fish species, colour change in eyes can be due to the absence or the presence of a dominant allele. It can also be involved in social rank or during reproduction. Different hormones and neuropeptides can modulate vocal features. It is hypothesized that a mutation or different hormonal concentrations could explain both sound amplitude and eye colour playing a role in animal communication in S. marginatus.

Commercial fisheries in a mega unregulated floodplain river: Assessment of the most favourable hydrological conditions for its preservation.

This paper deals with the hydrological variability effects on the primary commercial fish species inhabiting the main channel and the floodplain of the large Paraná River in its middle reaches in Argentina. Analysing more than eight decades (1935-2016) of information on the most frequent and abundant commercial species in conjunction with hydrological levels and temperature, our results show that spring-summer floods of a certain magnitude (c. 6 m) and durations (> 80 days) are crucial for sustaining commercial fisheries. Moreover, the frequency of these floods was modulated by the decadal climatic fluctuations that have occurred over the past 100 years in the Paraná Basin. An insight into the probable incidence of some anthropogenic influences is also provided.

Taxonomy of common taxa of Chlorophyceae (Chlorophyta) and Zygnematophyceae (Streptophyta) from periphyton of a Neotropical floodplain

Some orders of algal groups such as Chlorophyceae and Zygnematophyceae have been reported as frequent taxa in periphytic communities of wetlands. The present study aimed at submitting these algal members which occurred in high abundance and frequency in the periphyton of 30 environments of the Upper Paraná River floodplain to a taxonomic survey and to present some ecological data concerning their richness. Periphyton were collected from petioles by scraping of Eichhornia azurea (Sw.) Kunth and preserved with Lugol acetic solution in the Upper Paraná River, Brazil, during high water period in March 2010. Taxa were counted in inverted microscope and those higher than 2,500 individuals in density with frequency of occurrence less than 50% simultaneously in the 30 environments sampled were subjected to a detailed taxonomical treatment under optical microscope coupled to a light camera and ocular micrometer under 1000x. Identifications and descriptions were made according to the algal literature. Some abiotic data were shown. Fifteen taxa belonging to the classes Chlorophyceae and Zygnematophyceae were abundant representing 64.6% of the total density. A Procruste analysis within a Detrended Correspondence Analysis showed that distribution pattern of richness of clorophyceans and zygnematophyceans was represented by common species of these communities, highlighting the importance of knowing about these algae taxonomy

Fish fauna from the Paranapanema River basin, Brazil / Fauna de peixes da bacia do rio Paranapanema, Brasil

Abstract: The Paranapanema River is an important, extensively explored tributary of the Upper Paraná River basin. The fish fauna of the Paranapanema River has been investigated since the 1990s; however, no study has characterized the richness of fish species throughout the basin, including the main channel of the river, marginal lagoons, its tributaries, and sub-tributaries. Thus, we performed a review with 90 independent studies conducted at the upper, middle, and lower sections of the basin. We recorded 225 species, of which 165 were native, and 60 were non-native. We found that 77% of the species within the basin are composed by Siluriformes and Characiformes. Cichliformes had a significant number of non-native species established in impoundment sections of the basin. Incidence-Based Estimators (Bootstrap and Chao 2) demonstrated that the richness of native species is still underestimated. Some native (e.g., Hypostomus ancistroides) and non-native species (e.g., Plagioscion squamosissimus) are widely distributed in the basin, while others had a more restricted distribution. Among the registered species, the family Bryconidae had the highest number of representatives with threatened conservation status. In addition, we observed that the Capivara Reservoir and its tributaries were the most sampled regions, with the majority of studies performed in the Lower Paranapanema basin. The species richness recorded in large tributaries, such as Tibagi, Cinzas, Congonhas, and Pirapó rivers is critical for maintaining the fish fauna in the Paranapanema River. Our contribution may be used to support management actions and conservation strategies, as well as to indicate regions in the basin that need to be better inventoried.

Resumo: O rio Paranapanema é um importante tributário, amplamente explorado da bacia do Alto rio Paraná. A fauna de peixes do rio Paranapanema vem sendo investigada desde a década de 1990; no entanto, nenhum estudo caracterizou a riqueza de espécies de peixes em toda a bacia, incluindo o canal principal do rio, lagoas marginais, seus tributários e sub-tributários. Assim, realizamos uma revisão com 90 estudos independentes conduzidos nas regiões superior, média e inferior da bacia. Foram registradas 225 espécies, das quais 165 eram nativas e 60 eram não nativas. Verificamos que 77% das espécies dentro da bacia são compostas por Siluriformes e Characiformes. Cichliformes apresentou um número significativo de espécies não nativas estabelecidas em áreas de represamento da bacia. Estimadores de riqueza baseados em incidência (Bootstrap e Chao 2) demonstraram que a riqueza de espécies nativas ainda é subestimada. Algumas espécies nativas (e.g., Hypostomus ancistroides) e não nativas (e.g., Plagioscion squamosissimus) estão amplamente distribuídas na bacia, enquanto outras tem sua distribuição mais restrita. Entre as espécies registradas, a família Bryconidae obteve o maior número de representantes com status de conservação ameaçado. Além disso, observamos que o reservatório de Capivara e seus afluentes foram as regiões mais amostradas, sendo a maioria dos estudos realizados na bacia do baixo Paranapanema. A riqueza de espécies registrada em grandes afluentes, como os rios Tibagi, Cinzas, Congonhas e Pirapó, é fundamental para a manutenção da ictiofauna no rio Paranapanema. Nossa contribuição pode ser usada para apoiar ações de manejo e estratégias de conservação, bem como para indicar regiões na bacia que precisam ser melhor inventariadas.