Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes.

This study explores the interplay between digestive tract traits, food intake, and assimilation in omnivorous tetra fishes (Psalidodon bifasciatus, P. aff. gymnodontus, and Bryconamericus ikaa) from the Iguaçu River basin, an ecologically significant region known for high endemism. We hypothesize that variations in digestive tracts across species would be associated with differences in diet, isotopic composition in fish tissues, and overall diet assimilation. To test this, we employed stereoscopic and light microscopy to characterize the gross anatomy, histomorphology, and histochemistry of fish digestive tracts. Additionally, we used stomach content and stable isotope analyses to trace fish diets. While these tetra fishes shared histological structures, disparities were noted in anatomical digestive traits and diet preferences. The smallest species, B. ikaa, with a shorter intestine, had fewer pyloric caeca and primarily consumed animal-based diets. Conversely, P. bifasciatus and P. aff. gymnodontus, with longer intestines, displayed numerous pyloric caeca and consumed a balanced mix of animal and plant items. Despite anatomical and dietary differences, all three species predominantly assimilated animal-origin food. The tetra fishes had histological variations among digestive tract segments, with the esophagus having the thickest muscular layer, gradually thinning towards the posterior intestine. The final portion of the intestine exhibited a significant expansion in the lumen perimeter, while the esophagus had the smallest lumen area. Goblet cells were most concentrated in the posterior intestine for all species. The gross anatomy of these tetra fishes aligns with their omnivorous habit, while diet assimilation was dominated by animal-origin food. These findings provide crucial insights into the structural and tissue characteristics of their digestive systems, laying the groundwork for deeper exploration into the physiological aspects of their digestive tracts and enhancing our understanding of their feeding strategies.

Metals in species of the Cambeva (Teleostei: Trichomycteridae) genus of the Iguaçu River basin (Brazil).

The population growth is connected to the demand for resources and waste disposal in water. Metals are among several pollutants affecting aquatic ecosystems, posing risks to biota when in high concentrations. Metals can present a great danger to the aquatic ecosystem because they are not degradable and can bioaccumulate. Many rivers are already considered highly polluted. Among them is the Iguaçu River, located in southern Brazil, which is recognized for the Iguaçu Falls and its rate of endemism. One species of the Cambeva genus is among the endemic species found in the Iguaçu River and is threatened with extinction due to anthropization. Thus, we aimed to evaluate and compare the concentrations of copper, zinc, iron, lead, manganese, and cadmium in Cambeva stawiarski and Cambeva sp. 1 in four different streams of the Iguaçu River (Brazil). We collected 20 fish in two municipalities along the Iguaçu River tributaries. The results showed a statistical difference in the metal concentrations in different species and locations, mainly manganese, iron, and copper, observed in both species and municipalities and cadmium, which showed a statistical difference only for C. sp1. Fish from agricultural regions generally had the highest concentrations of metals, some above the permitted limits. Cadmium was found at high concentrations, generating great ecological concern since it is one of the most toxic metals, even in small quantities. The lack of limits in Brazilian legislation makes it challenging to predict the long-term effects of iron.

Effects of human disturbance on habitat and fish diversity in Neotropical streams.

Human pressures have been intensely modifying freshwater ecosystems worldwide. We assessed the effects of human pressure on habitat diversity and primary productivity to understand the consequences on fish fauna in 25 tropical and subtropical streams of two globally important ecoregions: Iguassu and Upper Paraná. We hypothesized that the increased human pressure (urbanization and agriculture) on stream environments, both at the local and catchment scales, directly decreases habitat diversity. We also hypothesized that increased human pressure triggers changes in primary productivity and fish fauna composition and structure. We evaluated the human pressure intensity using the Integrated Disturbance Index and the Rapid Habitat Diversity Assessment protocol, which combines information about land use, land cover and environmental characteristics of the stream catchment and sampling sites. Streams with increased human disturbance had lower habitat diversity, higher primary productivity, and high non-native species abundance. Fish compositional turnover was associated with increased human disturbance. Native and degradation-sensitive fish species, especially endemic ones, were associated with streams with higher habitat diversity and forested cover. Degradation-resistant fishes, mostly non-native species, were associated with streams with higher human disturbance and urban land use. Although human pressure did not affect species richness, Shannon diversity, and Simpson dominance, there were significant effects on numerical abundance and fish species equitability. In this study, human pressure directly affected habitat structure, with indirect consequences for fish fauna, increasing the potential for local extirpation of rare species.

Ichthyofauna in the last free-flowing river of the Lower Iguaçu basin: the importance of tributaries for conservation of endemic species.

The fish fauna from the Lower Iguaçu River and tributaries upstream of the Iguaçu Falls, the last free-flowing river stretch, were investigated. Twenty five sites in tributaries and the main channel were sampled between 2010 and 2016 using several kinds of fishing gear. The species were categorized according to their size, origin, and conservation status. Species richness and abundance in the main channel and tributaries were compared. In total, 87,702 specimens were recorded, comprising 76 species, 25 families, 53 genera, and eight orders. Characiformes and Siluriformes were the richest orders, representing 92% of the total specimens; Characidae, Cichlidae, Pimelodidae, and Loricariidae were the richest families. The fish fauna was composed of small and medium-sized species and included endemic (42%), autochthonous (24%), allochthonous (21%), and exotic (9%) species, as well as hybrids (4%). Significant differences in the relative numerical abundance of species were found among sites. Ancistrus mullerae and Rhamdia branneri (endemic) were indicator species for tributaries inside of Iguaçu National Park (INP), while Phalloceros harpagos (autochthonous) and Ictalurus punctatus (exotic) for tributaries outside of INP and Odontesthes bonariensis (allochthonous) for the main channel. The last dam-free stretch of the Lower Iguaçu River and tributaries upstream the Iguaçu Falls exhibits a rich endemic fish fauna, including some rare, endangered species (Steindachneridion melanodermatum, Gymnogeophagus taroba, and Psalidodon gymnogenys). These findings are essential to predict and understand the effects caused by the new Baixo Iguaçu Hydroelectric Power Plant and highlight the importance of tributaries and Iguaçu National Park for conservation of endemic species.

Histopathological alterations in gills of a fish (Astyanax bifasciatus) in neotropical streams: negative effects of riparian forest reduction and presence of pesticides.

The reduction of riparian vegetation around aquatic environments causes several physicochemical alterations and favors the entry of pesticides via surface runoff. Such changes have negative effects on aquatic organisms. In this study, we evaluated histopathological alterations in gills of Astyanax bifasciatus to test the hypothesis that more severe histopathological alterations occur in gills of fish from streams with higher agricultural impact from the surrounding area. The specimens were collected by electrofishing in seven streams of the lower Iguaçu basin between August 2015 and February 2016. The gills were processed according to routine histological methods and examined by light microscopy. The histopathological alterations, mainly stage II (lamellar aneurysm and total fusion of lamellae), were observed in fish collected in streams with higher agricultural activity. In these streams, the histopathological index indicated slight to moderate organ lesions. In contrast, in streams with more vegetation cover, fish collected presented stage I histopathological alterations (lamellar edema and lamellar hyperplasia), and the HI indicated normal functioning of the gills. In addition, chloride and acid mucous cells were more abundant in the gills of fish collected in rural streams. Our findings demonstrate that more severe histopathological alterations were registered in fish collected from streams with intense agricultural activity in the surrounding area. Therefore, it highlights that vegetation cover around the streams is a positive force for the conservation and health of aquatic organisms.

Influence of land use on the health of a detritivorous fish (Ancistrus mullerae) endemic to the Iguassu ecoregion: relationship between agricultural land use and severe histopathological alterations.

This study aimed to evaluate the histopathological biomarkers of the gills and liver of endemic catfish to test the hypothesis that, in environments under intense land use by agricultural activities, histopathological alterations occur more severely. Samples were collected by electrofishing in seven streams in the Lower Iguaçu basin quarterly from August 2015 to February 2016. The gills and livers were processed according to routine histological methods and examined by light microscopy. The histopathological alterations observed in fish from the streams with a higher percentage of natural vegetation cover were considered modest and indicated normal functioning of the organ (such as edema, hyperplasia, and leukocyte infiltration). As predicted, fish collected in streams with higher agricultural influence presented moderate to severe damage (aneurysm, vacuolization and cytoplasmic degeneration, and pyknotic nucleus). The abundance of chloride cells was significantly increased in the gills of Ancistrus mullerae collected in rural streams. In addition, in most streams, mucous cells were more abundant during the rainy period. Significant differences were observed in the histopathological index (HI) of the gills and livers, where severe histopathological alterations occurred in fish from streams with a higher agricultural influence. The observed alterations were more severe in the liver than in the gills, which are indeed related to the liver's key role in the detoxification of xenobiotics. We conclude that more severe histological alterations occurred in fish from streams with the highest land use by agricultural activities. Thus, our work provides important insight into the conservation and management of natural resources.

Fish fauna in forested and rural streams from an ecoregion of high endemism, lower Iguaçu River basin, Brazil / Fauna de peixe em riachos florestados e rurais de uma ecoregião de alto endemismo, bacia do baixo rio Iguaçu, Brasil

Abstract The fish fauna of eight streams with different land uses of their watersheds (forested and rural areas) in the lower Iguaçu River basin was inventoried, in order to evaluate the composition and species richness. The fishes were sampled quarterly from May 2015 to February 2016, using the electrofishing technique. In total, 4,239 individuals were captured, belonging to six orders, 11 families and 26 species. The orders Siluriformes and Characiformes, and the families Characidae and Trichomycteridae were the most specious. Of the total species sampled, 65% were endemic to the Iguaçu River basin, four are not described and four are non-native. As expected to the Iguaçu River basin, the inventoried fauna revealed low richness and high endemism, however was highly nested within the species composition reported for main channel of Iguaçu River and their larger tributaries. The species recorded here corresponded to a subset of 24.5% of the 106 species documented for the basin. The streams presented different faunas, with only two species (Astyanax bifasciatus and Trichomycterus stawiarski) common to both forested and rural streams. In addition, higher species richness was recorded in streams inserted in conservation units. The presence of non-native species was more frequent in rural streams. These results highlight the importance of the preservation of forested areas in the watersheds of lower Iguaçu, which presents a peculiar fish fauna, along with several threats to biodiversity such as habitat loss by intensive agriculture use.

Resumo A fauna de peixes foi inventariada em oito riachos com diferentes usos do entorno (áreas florestadas e rurais) na porção do baixo rio Iguaçu, em ordem para avaliar possíveis diferenças na composição e riqueza de espécies. Os peixes foram amostrados trimestralmente entre maio de 2015 e fevereiro de 2016, por meio da técnica de pesca elétrica. No total foram capturados 4239 indivíduos, pertencentes a seis ordens, 11 famílias e 26 espécies. As ordens Siluriformes e Characiformes foram as mais especiosas, assim como as famílias Characidae e Trichomycteridae. Do total de espécies amostradas, 65% foram endêmicas da bacia do rio Iguaçu, quatro foram não descritas e outras quatro foram não-nativas. Como esperado para a bacia do rio Iguaçu, a fauna inventariada revelou baixa riqueza e elevado endemismo, contudo, foi altamente aninhada dentro da composição de espécies relatada para o canal principal do rio Iguaçu e seus grandes tributários. As espécies aqui registradas corresponderam a um subconjunto de espécies de 24,5% das 106 documentadas para a bacia. Os riachos apresentaram faunas distintas, sendo que apenas duas espécies (Astyanax bifasciatus e Trichomycterus stawiarski) foram comuns a ambos os grupos de riachos florestados e rurais. Além disso, houve maior riqueza de espécies em riachos florestados. A presença de espécies não nativas foi maior em riachos rurais. Esses resultados ressaltam a importância da preservação de áreas florestadas nas bacias do baixo rio Iguaçu, as quais apresentam uma fauna de peixes peculiar, com várias ameaças para a biodiversidade tais como a perda de habitat por intensivo uso do solo pela agricultura.

Carnivory during Ontogeny of the Plagioscion squamosissimus: A Successful Non-Native Fish in a Lentic Environment of the Upper Paraná River Basin.

This study evaluated feeding patterns and ontogenetic variations in a non-native fish species (Plagioscion squamosissimus) in an isolated lake in the Upper Paraná River floodplain. Quarterly samplings were performed from April 2005 to February 2006 using plankton nets to capture larvae, seining nets for juveniles, and gill nets and trammel for adults. Stomach contents (n = 378) were examined according to the volumetric method in which the volume of each food item was estimated using graduated test tubes or a glass counting plate. During early development (larval stage), P. squamosissimus consumed mainly Cladocera and Copepoda. Juveniles showed a more diverse diet, including shrimp (Macrobrachium amazonicum), fish, aquatic insects (Trichoptera, Ephemeroptera, Chironomidae and pupae of Diptera) and plants. It was notable the high proportion of cannibalism (23.3%) in this stage. Adults consumed predominantly shrimp and fish. The use of food resources varied significantly between development stages (ANOSIM; r = 0.458; p<0.005), showing changes in food preferences during ontogeny. The Similarity Percentage Analysis (SIMPER) indicated that Cladocera and Copepoda were responsible for the differences observed between the larval stages of pre-flexion, flexion and post-flexion. M. amazonicum and Chironomidae were responsible for the differences between juvenile and larval stages, while M. amazonicum and other fishes caused the differences between adults and other ontogenetic stages. These results are confirmed by the relationship between standard length and developmental periods (ANCOVA; r2 = 0.94; p<0.0001). In general, there were low values of trophic niche breadth. The essentially carnivorous habit from the early stages of P. squamosissimus and the predominant use of M. amazonicum by adults have important roles in feeding patterns of the species, suggesting a major contribution to its success and establishment, especially in lentic environments.

Diet and ecomorphological relationships of an endemic, species-poor fish assemblage in a stream in the Iguaçu National Park

This study investigated the morphological and dietary relationships of the fish assemblage in a stream with an endemic fauna and low species richness. The ichthyofauna was sampled quarterly from September 2011 to July 2012, through the electrofishing technique. The stomach contents of 419 individuals belonging to seven species were analyzed by the volumetric method, and the ecomorphological traits of 30 specimens of each species were estimated. The main food items consumed were detritus, aquatic and terrestrial insects, and other aquatic invertebrates. We observed low levels of trophic niche breadth and diet overlap between most species. The PCA scores indicated the occurrence of three ecomorphotypes. PCA axis 1 segregated at one extreme, species with dorsoventrally depressed bodies, longer caudal peduncles, and well-developed swimming fins; and at the other extreme, species with compressed bodies and peduncles, and relatively larger eyes and anal fins. PCA axis 2 segregated species with elongated bodies and ventrally oblique mouths. The partial Mantel test revealed a significant correlation between diet and morphology, indicating independence from the phylogeny. The patterns observed suggest that the low richness did not result in a broadening of the species' trophic niches, or in the absence of some of the main ecomorphotypes expected.

Este estudo teve como objetivos investigar as relações morfológicas e alimentares de uma assembleia de peixes com fauna endêmica e de baixa riqueza de espécies. Os peixes foram amostrados trimestralmente entre setembro de 2011 a julho de 2012, através da técnica da pesca elétrica. Foram obtidas as medidas morfométricas que possibilitaram os cálculos dos índices ecomorfológicos e analisados os conteúdos estomacais de 419 indivíduos, pertencentes a sete espécies, através do método volumétrico. Os principais itens alimentares consumidos pela assembleia de peixes foram detrito, insetos aquáticos e terrestres e outros invertebrados aquáticos. Observou-se baixos valores de amplitude de nicho trófico e de sobreposição alimentar entre a maioria das espécies. Os escores da PCA, indicaram a ocorrência de três ecomorfotipos. O eixo CP1 segregou em um extremo espécies com corpo deprimido dorso-ventralmente, pedúnculo caudal longo e as nadadeiras desenvolvidas, enquanto no outro extremo, espécies com corpos e pedúnculos comprimidos, área dos olhos e das nadadeiras anais relativamente maiores. Por outro lado, o eixo CP2 segregou espécies com corpos mais alongados, bocas ventralmente oblíquas. Através do Teste de Mantel verificou-se relação significativa entre a dieta e a morfologia. Assim, os principais padrões tróficos e ecomorfológicos verificados sugerem que a baixa riqueza, não repercutiu no alargamento do nicho trófico das espécies ou na inexistência de algum dos principais grupos ecomorfológicos.