The construction of dams and hydroelectric plants affects biodiversity in aquatic environments and can facilitate the invasion of species. Few studies assess the long-term response of parasite fauna under these events. The aim of this study was to investigate possible changes in the endoparasite composition of the invasive catfish Trachelyopterus galeatus (Linnaeus, 1766) in the floodplain of the upper Paraná River over a 27-year study period. A total of 79 fish were collected in period 1 (1993) and 31 in period 2 (2019/2020) at the same sampling points, and the endoparasites were located in the gastrointestinal system using a stereomicroscope. It was found that the development of the fish and the composition of their endoparasitic fauna changed over time. In the second period, the fish presented smaller values for mass (g) and standard length (cm) when compared to period 1. It was found that three species of endoparasites were found per period, but although the richness was the same, the composition differed, and only one digenean (Microrchis oligovitellum Lunaschi, 1987 (Trematoda: Paramphistomidae)) was shared. The Porto Primavera Dam was built upstream of the site between the sampling periods (1999) and caused a number of environmental changes, possibly being the main factor responsible for changes in components of the parasite community. Anthropic modification to an environment can cause loss of diversity and loss of ecological interactions. Through our results, we emphasize the importance of including parasite fauna in studies that assess environmental impacts.

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.

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.
UNASSIGNED:
UNASSIGNED: The online version contains supplementary material available at 10.1007/s11160-022-09722-x.

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.

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.

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.

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.

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.

This study describes the invasion of the upper Paraná River basin by Pterygoplichthys ambrosettii based on a literature review and field samples. Pterygoplichthys ambrosettii has been reported in 42 localities throughout the upper Paraná River basin, including the Tietê, Paranapanema, Paraná, Grande and Aguapeí rivers. The ascent of P. ambrosettii after the inundation of the Sete Quedas Falls on the Paraná River and the release of individuals by aquarium hobbyists were the primary drivers of this invasion.

Twenty polymorphic microsatellite markers were developed for the Neotropical fish Leporinus obtusidens using a next generation sequencing approach and tested in two other characifomes species, Schizodon platae and Prochilodus lineatus. Microsatellite loci alleles in L. obtusidens ranged between 2 and 20 alleles per locus (mean = 5·7), with expected heterozygosity values ranging from 0·097 to 0·956 (mean = 0·578) and observed heterozygosity values ranging from 0·000 to 0·800 (mean = 0·400) in a sample of 20 specimens from the lower Paraná River (Argentina). Most of these markers will be a valuable tool for captive breeding and stocking programmes, as well as for analyses of population connectivity and genetic structure in this broadly distributed Neotropical migratory fish.