Composição e diversidade da ictiofauna em riachos do Cerrado, bacia do ribeirão Ouvidor, alto rio Paraná, Goiás, Brasil

Use of trophic ecology of omnivorous fish and abiotic factors as supporting tools for assessing environmental impacts in a neotropical river

The study of diet is one of the mechanisms by which competition for resources between species that cohabit in the same ecosystem can be inferred. Therefore, the relationships of the indices that measure specialization in the diet of fish species are necessary to characterize the nutritional quality of these populations and the ecosystem's environmental health. Three species of catfish were selected: one invasive (Clarias gariepinus) and two natives (Trachelyopterus striatulus and Rhamdia quelen), with similar distribution along the Guapi-Macacu River, in the Guapimirim Protection Area (Rio de Janeiro). Fifty-nine catfish of the three species were collected in total, along 32 collection points in the Guapi-Macacu River in two periods (dry and rainy) in 2018. Non-parametric statistics showed the partition of resources between species and the influence of abiotic factors (temperature, pH, transparency, and dissolved oxygen) contributing to the selection of available resources in the environment. Diet-related indices-repletion index (RI), condition factor (K), niche width, and trophic position (TP) of the specimens collected-contributed to measuring the nutritional status of each of these catfish species, showing that R. quelen has a relationship between RI and K, tending to absorb and metabolize nutrients faster than other species. In addition, the invasive species occupies a wide range of TPs compared to native species, confirming its feeding plasticity. On the contrary, T. striatulus needs large amounts of terrestrial insects to maintain its poor condition factor. Also, the RI showed direct influences of abiotic variables, with the temperature being the most prominent. Our results suggest that the invasive species can benefit from this environment that shows signs of environmental degradation.

DNA barcode and minibarcode identification of freshwater fishes from Cerrado headwater streams in Central Brazil

The extraordinary species diversity of the Neotropical freshwater fish fauna is world renown. Yet, despite rich species diversity, taxonomic and genetic resources for its Cerrado ichthyofauna remain poorly developed. We provide a reference library of 149 DNA barcodes for 39 species/lineages of Cerrado headwater stream fishes from the Brazilian Distrito Federal and nearby areas and test the utility of distance-based criteria, tree-based criteria and minibarcodes for specimen identification. Mean Kimura 2-parameter genetic distances within species to orders ranged 1·8-12·1%. However, mean intraspecific v. congeneric-interspecific distances (0·9-1·3%) overlapped extensively and distance-based barcoding failed to achieve correct identifications due to c. 4-12·1% error rates and 19·5% ambiguous identifications related to the presence of singletons. Overlap was reduced and best-match success rates improved drastically to 83·5% when Characidium barcodes representing potential misidentifications or undescribed species were removed. Tree-based monophyly criteria generally performed similarly to distance methods, correctly differentiating up to c. 85% of species/lineages despite neighbour-joining and Bayesian tree errors (random lineage-branching events, long-branch attraction). Five clusters (Ancistrus aguaboensis, Characidium spp., Eigenmannia trilineata, Hasemania hanseni and Hypostomus sp. 2) exhibited deep intraspecific divergences or para-/polyphyly and multiple Barcode Index Number assignments indicative of putative candidate species needing taxonomic re-examination. Sliding-window analyses also indicated that a 200 bp minibarcode region performed just as well at specimen identification as the entire barcode gene. Future DNA barcoding studies of Distrito Federal-Cerrado freshwater fishes will benefit from increased sampling coverage, as well as consideration of minibarcode targets for degraded samples and next-generation sequencing.

Seasonal and longitudinal variation in fish assemblage structure along an unregulated stretch of the Middle Uruguay River

ABSTRACT Diversity patterns and their causes remain important questions, especially for ecosystems that preserve natural conditions. This is the case of fish diversity in large Neotropical rivers. In this context, we investigated fish diversity patterns along an extensive unregulated river section (ca. 450 km) in the Middle Uruguay River Basin. Sampling was conducted seasonally between May 2017 and March 2018, at six sites (patches) with contrasting environmental conditions. We collected 3,008 individuals belonging to 90 species. Nine were migratory, which summed relevant biomass in local assemblages (20 to 60%). We observed spatial variation in assemblage structure, but weak seasonal effects. Overall, biomass was similar among sites, but richness tended to increase downstream. Migratory fishes showed opposed trends, with higher richness and biomass upstream, particularly catfishes (Siluriformes). Ordination analyses separated sites in three groups based on variations in composition and abundance, and revealed associations between these groups and specific hydro-geomorphic conditions (i.e., flow, depth, channel width and the presence of riparian vegetation). Our study revealed that fish diversity distributes heterogeneously along the main channel, where hydro-geomorphic patches select for distinct assemblages along riverine gradients.

Diversidade da ictiofauna de riachos de cabeceira em paisagens antropizadas na bacia do Alto Paraguai

RESUMO A estruturação das assembleias de peixes em riachos de cabeceira sofre forte influência dos modelos de uso e ocupação do solo. O avanço da fronteira agrícola tem se mostrado uma das principais ameaças às comunidades desses ambientes. Este estudo teve como objetivo avaliar a influência das formas de uso e ocupação do solo sobre a estrutura da comunidade de peixes em riachos de cabeceira, localizados na bacia do Alto Paraguai, Mato Grosso, Brasil. As amostragens foram realizadas nos riachos Ararão, Queima Pé e Russo, no município de Tangará da Serra, MT, usando rede de arrasto e peneira, entre os meses de julho e dezembro de 2013. Foram coletados 4.192 indivíduos pertencentes a 35 espécies, sendo que Moenkhausia lopesi (Britski & de Silimon, 2001) e Knodus moenkhausii (Eigenmann & Kennedy, 1903) mostraram-se dominantes, representando 68,5% dos indivíduos amostrados. A riqueza e abundância não apresentaram diferenças significativas entre os três riachos, porém o índice de diversidade de Shannon foi maior no riacho Russo (H´ = 2,33). Os altos percentuais de conversão da vegetação nativa em campos de agricultura (49,20%) e pecuária (30,69%), revelaram forte relação negativa da agricultura com a riqueza, indicando que quanto menor a área de agricultura maior é a riqueza.

Oogenesis in Laetacara araguaiae (Ottoni and Costa, 2009) (Labriformes: Cichlidae)

We aimed to analyze the oogenesis of adult females of the cichlid fish Laetacara araguaiae. The specimens' gonads were removed and processed for light and transmission electron microscopy. Oogenesis in L. araguaiae showed the following characteristics: a germinal epithelium with three types of oogonia (A-undifferentiated, A-differentiated and B-oogonia), oocytes at meiotic prophase stage and ovarian follicle formation. Oocytes showing primary growth with pre-vitellogenic and cortical alveolus were observed. Similar to data for other cichlids, oocytes in secondary growth or vitellogenesis were characterized by the initial deposition of yolk microgranules. The event that characterizes the maturation stage is nucleolus migration, also called the germinal vesicle, to the oocyte periphery in the direction of the micropyle. The follicular complex undergoes several changes throughout the oocyte stages. To the best of our knowledge this study is the first to describe L. araguaiae oogenesis. Moreover, this study is the first step to better understand the reproductive biology of this species, which shows great potential for use as an ornamental fish.

Estrutura da ictiofauna do rio Bonito, bacia hidrográfica do rio Ivaí, sistema alto rio Paraná, Brasil

A diversidade da ictiofauna da bacia do rio Ivaí é altamente subestimada. O presente estudo teve como objetivo caracterizar a ictiofauna do rio Bonito, um tributário do rio Ivaí, bacia do alto rio Paraná, quanto à riqueza, diversidade e constância de espécies. Foram estabelecidos três locais de amostragem ao longo do gradiente longitudinal do rio: cabeceira, trecho médio e região de desembocadura próxima ao rio Ivaí. Três incursões de coleta foram feitas em cada unidade utilizando redes de espera de diferentes malhas, tarrafas e covos. A ictiofauna foi composta por 23 espécies, divididas em nove famílias e três ordens. Entre as espécies coletadas, três delas são possíveis novos registros para o alto rio Paraná e 12 para a bacia do rio Ivaí. A maior riqueza foi registrada no trecho inferior, onde foram encontradas 20 espécies, o qual também apresentou maior diversidade e menor dominância de espécies. No trecho médio do rio foram coletadas sete espécies e no trecho superior apenas uma. No baixo rio Bonito a maioria das espécies foram acessórias e no trecho médio cinco foram constantes e apenas uma acessória. O trecho médio apresentou maior dominância de espécies, com destaque para Hypostomus aff. ancistroides. O gradiente altitudinal foi um importante fator estruturador da assembleia de peixes do rio Bonito, delimitando as assembleias ao longo do gradiente longitudinal.

Structure and integrity of fish assemblages in streams associated to conservation units in Central Brazil

This study aims to characterize the spatial and seasonal distribution of the fish assemblage and evaluate the integrity of streams in a sustainable use area that includes integral protection conservation units in Distrito Federal, Central Brazil (Cerrado biome). For the study, 12 stretches of 8 streams were sampled in 2008 (dry season) and 2009 (wet season). For that evaluation was estimated the Physical Habitat Index (PHI), vegetation cover (VC), pH, dissolved oxygen, turbidity, and conductivity. We recorded 22 species, about eight undescribed species, by a total of 2,327 individuals. The most representative families in number of species were Characidae (31.8%), Loricariidae (31.8%), and Crenuchidae (13.6%). Knodus moenkhausii was the most abundant species with 1,476 individuals, added to Astyanax sp., Phalloceros harpagos, and Hasemania sp. they represent over 95% of the total abundance. The species Astyanax sp. (occurring in 79.2% of the stretches) and K. moenkhausii (50.0%) were considered constant in both seasons. The longitudinal gradient (River Continuum) exerts a strong influence on the studied assemblage. According to CCA, the variables that structure the fish assemblage are based on aspects related to water volume and habitat complexity. No seasonal variation in richness, diversity, abundance, and mass were detected. A cluster analysis suggests a separation of species composition between the stretches of higher and lower orders, which was not observed for seasonality. The streams were considered well preserved (mean PHI 82.9±7.5%), but in some stretches were observed anthropogenic influence, detected in the water quality and, mainly, on the riparian vegetation integrity. The exotic species Poecilia reticulata was sampled in the two stretches considered most affected by anthropogenic activities by PHI, conductivity, and VC.

Ictiofauna dos córregos do Parque Nacional de Brasília, bacia do Alto Rio Paraná, Distrito Federal, Brasil Central

O objetivo do presente estudo foi realizar o inventário da fauna íctica dos córregos do Parque Nacional de Brasília no Distrito Federal e caracterizar a estrutura da comunidade íctica ao longo dos cursos d'água. Foram amostrados córregos das sub-bacias do Bananal e Santa Maria/Torto na região hidrográfica do Alto Rio Paraná. Esses cursos d'água apresentam bom estado de preservação, evidenciado na integridade de suas características ambientais naturais e na manutenção dos componentes biológicos nativos. Um total de 8.614 indivíduos, distribuídos em quatro ordens e nove famílias, foram coletados. A ordem com maior número de espécies foi a Characiformes, seguida por Siluriformes. Das 28 espécies encontradas 11 são novas para a ciência. Apenas a espécie exótica Poecilia reticulata foi encontrada. Astyanax sp. e Hyphessobrycon balbus foram as espécies com maior distribuição na área de estudo e Knodus moenkhausii apresentou a maior abundância (64,5% dos indivíduos). Nos trechos com maiores larguras e profundidades foram encontrados maiores valores de riqueza de espécies e abundância de indivíduos.