Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers.

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate- and fish-based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3-class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen-Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico-chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity.

Rainforest metropolis casts 1,000-km defaunation shadow.

Tropical rainforest regions are urbanizing rapidly, yet the role of emerging metropolises in driving wildlife overharvesting in forests and inland waters is unknown. We present evidence of a large defaunation shadow around a rainforest metropolis. Using interviews with 392 rural fishers, we show that fishing has severely depleted a large-bodied keystone fish species, tambaqui (Colossoma macropomum), with an impact extending over 1,000 km from the rainforest city of Manaus (population 2.1 million). There was strong evidence of defaunation within this area, including a 50% reduction in body size and catch rate (catch per unit effort). Our findings link these declines to city-based boats that provide rural fishers with reliable access to fish buyers and ice and likely impact rural fisher livelihoods and flooded forest biodiversity. This empirical evidence that urban markets can defaunate deep into rainforest wilderness has implications for other urbanizing socioecological systems.

Disentangling the pathways of land use impacts on the functional structure of fish assemblages in Amazon streams.

Agricultural land use is a primary driver of environmental impacts on streams. However, the causal processes that shape these impacts operate through multiple pathways and at several spatial scales. This complexity undermines the development of more effective management approaches, and illustrates the need for more in-depth studies to assess the mechanisms that determine changes in stream biodiversity. Here we present results of the most comprehensive multi-scale assessment of the biological condition of streams in the Amazon to date, examining functional responses of fish assemblages to land use. We sampled fish assemblages from two large human-modified regions, and characterized stream conditions by physical habitat attributes and key landscape-change variables, including density of road crossings (i.e. riverscape fragmentation), deforestation, and agricultural intensification. Fish species were functionally characterized using ecomorphological traits describing feeding, locomotion, and habitat preferences, and these traits were used to derive indices that quantitatively describe the functional structure of the assemblages. Using structural equation modeling, we disentangled multiple drivers operating at different spatial scales, identifying causal pathways that significantly affect stream condition and the structure of the fish assemblages. Deforestation at catchment and riparian network scales altered the channel morphology and the stream bottom structure, changing the functional identity of assemblages. Local deforestation reduced the functional evenness of assemblages (i.e. increased dominance of specific trait combinations) mediated by expansion of aquatic vegetation cover. Riverscape fragmentation reduced functional richness, evenness and divergence, suggesting a trend toward functional homogenization and a reduced range of ecological niches within assemblages following the loss of regional connectivity. These results underscore the often-unrecognized importance of different land use changes, each of which can have marked effects on stream biodiversity. We draw on the relationships observed herein to suggest priorities for the improved management of stream systems in the multiple-use landscapes that predominate in human-modified tropical forests.

Wood stock in neotropical streams: Quantifying and comparing instream wood among biomes and regions.

Instream wood plays important chemical, physical and ecological functions in aquatic systems, benefiting biota directly and indirectly. However, human activities along river corridors have disrupted wood recruitment and retention, usually leading to reductions in the amount of instream wood. In the tropics, where wood is believed to be more transient, the expansion of agriculture and infrastructure might be reducing instream wood stock even more than in the better studied temperate streams. However, research is needed to augment the small amount of information about wood in different biomes and ecosystems of neotropical streams. Here we present the first extensive assessment of instream wood loads and size distributions in streams of the wet-tropical Amazon and semi-humid-tropical Cerrado (the Brazilian savanna). We also compare neotropical wood stocks with those in temperate streams, first comparing against data from the literature, and then from a comparable dataset from temperate biomes in the USA. Contrary to our expectations, Amazon and Cerrado streams carried similar wood loads, which were lower than the world literature average, but similar to those found in comparable temperate forest and savanna streams in the USA. Our results indicate that the field survey methods and the wood metric adopted are highly important when comparing different datasets. But when properly compared, we found that most of the wood in temperate streams is made-up of a small number of large pieces, whereas wood in neotropical streams is made up of a larger number of small pieces that produce similar total volumes. The character of wood volumes among biomes is linked more to the delivery, transport and decomposition mechanisms than to the total number of pieces. Future studies should further investigate the potential instream wood drivers in neotropical catchments in order to better understand the differences and similarities here detected between biomes and climatic regions.

Elements of fish metacommunity structure in Neotropical freshwater streams.

The identification of the mechanisms underlying patterns of species co-occurrence is a way to identify which process(es) (niche, neutral, or both) structure metacommunities. The current paper had the goal of identifying patterns of co-occurrence in Neotropical stream fish and determining which processes structure the fish metacommunity, and identifying any gradients underlying this structure. Results indicated that the metacommunity formed by the species pool was structured by a pattern of nested co-occurrence (hyperdispersed species loss) and a mass-effect mechanism. However, a set of core species, displaying a Clementsian pattern, was structured by a species-sorting mechanism. Both, hyperdispersed species loss and the Clementsian patterns point to a discrete set of communities within the metacommunity. These communities could be isolated by the water physicochemical conditions or morphological characteristics of the stream channel.

Integrated terrestrial-freshwater planning doubles conservation of tropical aquatic species.

Conservation initiatives overwhelmingly focus on terrestrial biodiversity, and little is known about the freshwater cobenefits of terrestrial conservation actions. We sampled more than 1500 terrestrial and freshwater species in the Amazon and simulated conservation for species from both realms. Prioritizations based on terrestrial species yielded on average just 22% of the freshwater benefits achieved through freshwater-focused conservation. However, by using integrated cross-realm planning, freshwater benefits could be increased by up to 600% for a 1% reduction in terrestrial benefits. Where freshwater biodiversity data are unavailable but aquatic connectivity is accounted for, freshwater benefits could still be doubled for negligible losses of terrestrial coverage. Conservation actions are urgently needed to improve the status of freshwater species globally. Our results suggest that such gains can be achieved without compromising terrestrial conservation goals.

Migratory fishes from rivers to reservoirs: seasonal and longitudinal perspectives

Migratory fishes have high ecological, social, and commercial value, and are strongly affected by river regulation. This study aimed to understand how migratory fishes use the longitudinal gradient, in an upstream to downstream direction of two free-flowing rivers and two reservoirs in a cascade within the Upper Grande River Basin, Brazil. The numeric abundance, biomass, richness, presence of fingerlings and juveniles, and the macroscopic gonadal maturation stage of migratory fishes were ascertained and evaluated bimonthly for two years. Recruitment in migratory fishes seems to rely completely on the free-flowing rivers upstream and their floodplains. Transition areas do not seem to have a significant role in recruitment. Therefore, we highlight the importance of maintaining the free flow of rivers and the integrity of their floodplains.

Is environmental legislation conserving tropical stream faunas? A large-scale assessment of local, riparian and catchment-scale influences on Amazonian fish.

Agricultural expansion and intensification are major threats to tropical biodiversity. In addition to the direct removal of native vegetation, agricultural expansion often elicits other human-induced disturbances, many of which are poorly addressed by existing environmental legislation and conservation programmes. This is particularly true for tropical freshwater systems, where there is considerable uncertainty about whether a legislative focus on protecting riparian vegetation is sufficient to conserve stream fauna.To assess the extent to which stream fish are being effectively conserved in agricultural landscapes, we examined the spatial distribution of assemblages in river basins to identify the relative importance of human impacts at instream, riparian and catchment scales, in shaping observed patterns. We used an extensive dataset on the ecological condition of 83 low-order streams distributed in three river basins in the eastern Brazilian Amazon.We collected and identified 24,420 individual fish from 134 species. Multiplicative diversity partitioning revealed high levels of compositional dissimilarity (DS) among stream sites (DS = 0.74 to 0.83) and river basins (DS = 0.82), due mainly to turnover (77.8% to 81.8%) rather than nestedness. The highly heterogeneous fish faunas in small Amazonian streams underscore the vital importance of enacting measures to protect forests on private lands outside of public protected areas.Instream habitat features explained more variability in fish assemblages (15%-19%) than riparian (2%-12%), catchment (4%-13%) or natural covariates (4%-11%). Although grouping species into functional guilds allowed us to explain up to 31% of their abundance (i.e. for nektonic herbivores), individual riparian - and catchment - scale predictor variables that are commonly a focus of environmental legislation explained very little of the observed variation (partial R2 values mostly <5%).Policy implications. Current rates of agricultural intensification and mechanization in tropical landscapes are unprecedented, yet the existing legislative frameworks focusing on protecting riparian vegetation seem insufficient to conserve stream environments and their fish assemblages. To safeguard the species-rich freshwater biota of small Amazonian streams, conservation actions must shift towards managing whole basins and drainage networks, as well as agricultural practices in already-cleared land.

Urban market amplifies strong species selectivity in Amazonian artisanal fisheries

Despite Amazonia possessing the highest freshwater biodiversity on Earth, urban landing data show how huge fishing pressure is placed on only a dozen species. However, truly characterising the fishery and understanding the drivers of species selectivity is challenging, given the neglect of artisanal fishing activity, who may catch most of the Amazon's fish. We register the catch of 824 fishing trips by interviewing artisanal fishers in their rural riverside communities. We use these data to characterise the artisanal fishery of the Rio Purus, the main fish source sub-system for the Amazon's largest city (Manaus), and investigate the factors determining catch composition. Fishers caught 80 fish species, yet just four species made up over half of the harvested biomass. Urban markets appear to drive greater selectivity, with a significantly lower species diversity in commercial compared to subsistence catches. Fish catch composition varied significantly both seasonally and with geographical remoteness from Manaus. The spatial turnover in catch composition appears to be driven by urban access, with more commercially important species dominating where Manaus-based fish-buyers frequent. Our data may partially explain observed overfishing in some commercially important species, particularly as most Amazonians now live in urban areas.(AU)

Apesar da Amazônia possuir a maior biodiversidade de água doce do mundo, dados de desembarques urbanos mostram como a grande pressão da pesca é focada em apenas uma dúzia de espécies. Entretanto, caracterizar a pesca e entender as causas da seletividade das espécies é desafiador pela pesca artesanal, que pode capturar a maioria dos peixes da Amazônia, ser negligenciada. Registramos as capturas de 824 pescarias entrevistando pescadores artesanais em suas comunidades ribeirinhas. Usamos esses dados para caracterizar a pesca artesanal do rio Purus, o principal subsistema de origem do pescado para a maior cidade da Amazônia (Manaus), e investigamos os fatores que determinam a composição das capturas. Os pescadores capturaram 80 espécies de peixes, e apenas quatro representaram mais da metade da biomassa. Os mercados urbanos parecem direcionar maior seletividade, com diversidade de espécies significativamente menor nas capturas comerciais que nas de subsistência. A composição do pescado variou significativamente tanto sazonalmente quanto com o afastamento geográfico de Manaus. A substituição espacial na composição das capturas parece ser direcionada pelo acesso urbano, com espécies comercialmente importantes dominando onde os compradores de peixes de Manaus frequentam. Nossos dados podem explicar parcialmente a sobrepesca observada de algumas espécies comercialmente importantes, particularmente porque a maioria da população da Amazônia vive atualmente em áreas urbanas.(AU)

Urban market amplifies strong species selectivity in Amazonian artisanal fisheries

Despite Amazonia possessing the highest freshwater biodiversity on Earth, urban landing data show how huge fishing pressure is placed on only a dozen species. However, truly characterising the fishery and understanding the drivers of species selectivity is challenging, given the neglect of artisanal fishing activity, who may catch most of the Amazon's fish. We register the catch of 824 fishing trips by interviewing artisanal fishers in their rural riverside communities. We use these data to characterise the artisanal fishery of the Rio Purus, the main fish source sub-system for the Amazon's largest city (Manaus), and investigate the factors determining catch composition. Fishers caught 80 fish species, yet just four species made up over half of the harvested biomass. Urban markets appear to drive greater selectivity, with a significantly lower species diversity in commercial compared to subsistence catches. Fish catch composition varied significantly both seasonally and with geographical remoteness from Manaus. The spatial turnover in catch composition appears to be driven by urban access, with more commercially important species dominating where Manaus-based fish-buyers frequent. Our data may partially explain observed overfishing in some commercially important species, particularly as most Amazonians now live in urban areas.(AU)

Apesar da Amazônia possuir a maior biodiversidade de água doce do mundo, dados de desembarques urbanos mostram como a grande pressão da pesca é focada em apenas uma dúzia de espécies. Entretanto, caracterizar a pesca e entender as causas da seletividade das espécies é desafiador pela pesca artesanal, que pode capturar a maioria dos peixes da Amazônia, ser negligenciada. Registramos as capturas de 824 pescarias entrevistando pescadores artesanais em suas comunidades ribeirinhas. Usamos esses dados para caracterizar a pesca artesanal do rio Purus, o principal subsistema de origem do pescado para a maior cidade da Amazônia (Manaus), e investigamos os fatores que determinam a composição das capturas. Os pescadores capturaram 80 espécies de peixes, e apenas quatro representaram mais da metade da biomassa. Os mercados urbanos parecem direcionar maior seletividade, com diversidade de espécies significativamente menor nas capturas comerciais que nas de subsistência. A composição do pescado variou significativamente tanto sazonalmente quanto com o afastamento geográfico de Manaus. A substituição espacial na composição das capturas parece ser direcionada pelo acesso urbano, com espécies comercialmente importantes dominando onde os compradores de peixes de Manaus frequentam. Nossos dados podem explicar parcialmente a sobrepesca observada de algumas espécies comercialmente importantes, particularmente porque a maioria da população da Amazônia vive atualmente em áreas urbanas.(AU)

Land-use changes affect the functional structure of stream fish assemblages in the Brazilian Savanna

We investigated the mechanisms involved in the relationship between land-use changes and aquatic biodiversity, using stream fish assemblages of the Brazilian Savanna (i.e., Cerrado) as a study model. We tested the prediction that landscape degradation would decrease environmental heterogeneity and change predominant physical-habitat types, which in turn would decrease the functional diversity and alter the functional identity of fish assemblages. We sampled fish from 40 streams in the Upper Paraná River basin, and assessed catchment and instream conditions. We then conducted an ecomorphological analysis to functionally characterize all species (36) and quantify different facets of the functional structure of assemblages. We detected multiple pathways of the impacts from landscape changes on the fish assemblages. Catchment degradation reduced the stream-bed complexity and the heterogeneity of canopy shading, decreasing assemblage functional specialization and divergence. Landscape changes also reduced the water volume and the amount of large rocks in streams, resulting in decreased abundances of species with large bodies and with morphological traits that favor swimming in the water column. We conclude that land-use intensification caused significant changes in aquatic biodiversity in the Cerrado, reinforcing the need to pay special attention to this global hotspot.(AU)

Investigamos os mecanismos envolvidos na relação entre mudanças de uso da terra e biodiversidade aquática, utilizando a ictiofauna de riachos do Cerrado como modelo de estudo. Testamos a predição de que a degradação da paisagem reduz a heterogeneidade ambiental e muda os tipos predominantes de habitat, por sua vez, diminuindo a diversidade e alterando a identidade funcional de comunidades de peixes. Amostramos 40 riachos da bacia do Alto Rio Paraná, e avaliamos as condições da drenagem e do habitat físico local. Em seguida, conduzimos uma análise ecomorfológica para caracterizar funcionalmente todas as espécies (36) e quantificar diferentes facetas da estrutura funcional das comunidades. Detectamos múltiplos caminhos de impacto das alterações da paisagem sobre a ictiofauna. A degradação das bacias de drenagem reduziu complexidade do leito e heterogeneidade no sombreamento pelo dossel, diminuindo especialização e divergência funcional das comunidades. Alterações na paisagem também reduziram volume de água e quantidade de pedras grandes nos riachos, resultando em diminuição na abundância de espécies de maior porte e com atributos morfológicos que favorecem a natação na coluna d'água. Concluímos que a intensificação dos usos da terra causa alterações significativas para a biodiversidade aquática no Cerrado, reforçando a necessidade de especial atenção a este hotspot global.(AU)

Human impacts and the loss of Neotropical freshwater fish diversity

Neotropical Ichthyology promotes the Special Issue (SI) "Human impacts and the loss of Neotropical freshwater fish diversity" with the purpose of publishing relevant scientific articles on the current biodiversity crisis and the loss of Neotropical freshwater fishes in the Anthropocene. The SI is composed of 22 publications, being two review articles and 20 original articles. A total of 107 researchers contributed to these papers, involving 44 institutions based in Brazil and six other countries. Published articles investigated main anthropic activities and their impacts on fish diversity, with special focus on river regulation, mining, land use changes, aquaculture, and fisheries. Studies provided evidence about the loss of fish diversity in the Neotropics, including fish kill events, demographic changes, contamination, changes in assemblage structure, loss of taxonomic and functional diversity, besides the degradation of ecosystem functions and services, and the lack of effective protection and conservation. Studies were conducted in rivers, streams, lakes, and reservoirs from different Neotropical systems. The studies published in this SI represent a relevant sample of the current worrisome situation of freshwater fishes in the Neotropical region and call for urgent revision in environmental policies, management and conservation initiatives, and socioeconomic priorities.(AU)

A revista Neotropical Ichthyology lança o Volume Especial (SI) "Human impacts and the loss of Neotropical freshwater fish diversity" com o objetivo de publicar artigos científicos relevantes sobre a atual crise da biodiversidade e a perda de diversidade de peixes de água doce Neotropicais no Antropoceno. O SI é composto por 22 publicações, sendo dois artigos de revisão e 20 artigos originais. Um total de 107 pesquisadores contribuíram com esses artigos, envolvendo 44 instituições sediadas no Brasil e em seis outros países. Os artigos publicados investigaram as principais atividades antrópicas e seus impactos sobre a diversidade de peixes, com foco especial na regulação dos rios, mineração, mudanças no uso do solo, aquicultura e pesca. Os estudos forneceram evidências sobre a perda de diversidade de peixes na região Neotropical, incluindo eventos de mortandade, alterações demográficas, contaminação, mudanças na estrutura das assembleias, perda de diversidade taxonômica e funcional, além da degradação de funções e serviços ecossistêmicos, e falta de ações efetivas de proteção e conservação. Os estudos foram conduzidos em rios, riachos, lagos e reservatórios de diferentes sistemas Neotropicais. Os estudos publicados neste SI representam uma amostra relevante da atual situação dos peixes de água doce na região Neotropical, reforçando a necessidade de revisão das políticas ambientais, ações de manejo e conservação, e prioridades socioeconômicas.(AU)

Human impacts and the loss of Neotropical freshwater fish diversity

Neotropical Ichthyology promotes the Special Issue (SI) "Human impacts and the loss of Neotropical freshwater fish diversity" with the purpose of publishing relevant scientific articles on the current biodiversity crisis and the loss of Neotropical freshwater fishes in the Anthropocene. The SI is composed of 22 publications, being two review articles and 20 original articles. A total of 107 researchers contributed to these papers, involving 44 institutions based in Brazil and six other countries. Published articles investigated main anthropic activities and their impacts on fish diversity, with special focus on river regulation, mining, land use changes, aquaculture, and fisheries. Studies provided evidence about the loss of fish diversity in the Neotropics, including fish kill events, demographic changes, contamination, changes in assemblage structure, loss of taxonomic and functional diversity, besides the degradation of ecosystem functions and services, and the lack of effective protection and conservation. Studies were conducted in rivers, streams, lakes, and reservoirs from different Neotropical systems. The studies published in this SI represent a relevant sample of the current worrisome situation of freshwater fishes in the Neotropical region and call for urgent revision in environmental policies, management and conservation initiatives, and socioeconomic priorities.(AU)

A revista Neotropical Ichthyology lança o Volume Especial (SI) "Human impacts and the loss of Neotropical freshwater fish diversity" com o objetivo de publicar artigos científicos relevantes sobre a atual crise da biodiversidade e a perda de diversidade de peixes de água doce Neotropicais no Antropoceno. O SI é composto por 22 publicações, sendo dois artigos de revisão e 20 artigos originais. Um total de 107 pesquisadores contribuíram com esses artigos, envolvendo 44 instituições sediadas no Brasil e em seis outros países. Os artigos publicados investigaram as principais atividades antrópicas e seus impactos sobre a diversidade de peixes, com foco especial na regulação dos rios, mineração, mudanças no uso do solo, aquicultura e pesca. Os estudos forneceram evidências sobre a perda de diversidade de peixes na região Neotropical, incluindo eventos de mortandade, alterações demográficas, contaminação, mudanças na estrutura das assembleias, perda de diversidade taxonômica e funcional, além da degradação de funções e serviços ecossistêmicos, e falta de ações efetivas de proteção e conservação. Os estudos foram conduzidos em rios, riachos, lagos e reservatórios de diferentes sistemas Neotropicais. Os estudos publicados neste SI representam uma amostra relevante da atual situação dos peixes de água doce na região Neotropical, reforçando a necessidade de revisão das políticas ambientais, ações de manejo e conservação, e prioridades socioeconômicas.(AU)

Land-use changes affect the functional structure of stream fish assemblages in the Brazilian Savanna

We investigated the mechanisms involved in the relationship between land-use changes and aquatic biodiversity, using stream fish assemblages of the Brazilian Savanna (i.e., Cerrado) as a study model. We tested the prediction that landscape degradation would decrease environmental heterogeneity and change predominant physical-habitat types, which in turn would decrease the functional diversity and alter the functional identity of fish assemblages. We sampled fish from 40 streams in the Upper Paraná River basin, and assessed catchment and instream conditions. We then conducted an ecomorphological analysis to functionally characterize all species (36) and quantify different facets of the functional structure of assemblages. We detected multiple pathways of the impacts from landscape changes on the fish assemblages. Catchment degradation reduced the stream-bed complexity and the heterogeneity of canopy shading, decreasing assemblage functional specialization and divergence. Landscape changes also reduced the water volume and the amount of large rocks in streams, resulting in decreased abundances of species with large bodies and with morphological traits that favor swimming in the water column. We conclude that land-use intensification caused significant changes in aquatic biodiversity in the Cerrado, reinforcing the need to pay special attention to this global hotspot.(AU)

Investigamos os mecanismos envolvidos na relação entre mudanças de uso da terra e biodiversidade aquática, utilizando a ictiofauna de riachos do Cerrado como modelo de estudo. Testamos a predição de que a degradação da paisagem reduz a heterogeneidade ambiental e muda os tipos predominantes de habitat, por sua vez, diminuindo a diversidade e alterando a identidade funcional de comunidades de peixes. Amostramos 40 riachos da bacia do Alto Rio Paraná, e avaliamos as condições da drenagem e do habitat físico local. Em seguida, conduzimos uma análise ecomorfológica para caracterizar funcionalmente todas as espécies (36) e quantificar diferentes facetas da estrutura funcional das comunidades. Detectamos múltiplos caminhos de impacto das alterações da paisagem sobre a ictiofauna. A degradação das bacias de drenagem reduziu complexidade do leito e heterogeneidade no sombreamento pelo dossel, diminuindo especialização e divergência funcional das comunidades. Alterações na paisagem também reduziram volume de água e quantidade de pedras grandes nos riachos, resultando em diminuição na abundância de espécies de maior porte e com atributos morfológicos que favorecem a natação na coluna d'água. Concluímos que a intensificação dos usos da terra causa alterações significativas para a biodiversidade aquática no Cerrado, reforçando a necessidade de especial atenção a este hotspot global.(AU)

Ecological separation by ecomorphology and swimming performance between two congeneric fish species

The high diversity of freshwater fish species reflects a great morphological plasticity. Understanding the relationship between swimming capacity, morphology and habitat use may be important to predict the chances of finding a species at an anthropized environment. The swimming capacity and morphological aspects of two sympatric species of Characidium, and for which spatial segregation in different hydraulic habitats is known, were compared in this study. Twenty-one individuals of Characidium fasciatum Reinhardt, 1867 and 23 individuals of Characidium cf. zebra Eigenmann, 1909 were captured and used for the evaluation of the swimming capacity and ecomorphological attributes. The swimming capacity of each species was obtained by measuring critical and relative velocities. A total of 12 ecomorphological attributes correlated with habitat use and swimming characteristics were also compared. The Mann-Whitney mean test showed that the swimming capacity of C. fasciatum was greater than that of C. cf. zebra, and the standard length of the individuals explained 12.42% of the variation in their capacity to withstand water flow. Both species were morphologically distinct in the relative length of the caudal peduncle, ventral flattening index and the relative area of the pectoral fin. The relative area of the pectoral fin alone accounted for 16.71% of the differences in the ability to resist the water flow and which were not explained by body length. Our results showed that two species differed in the ecomorphological space and in their swimming capacity, supporting the hypothesis that the greater the hydrodynamism, the better a fish is able to withstand the water flow, and that this capacity is correlated with the morphological characteristics linked to the swimming activity of the fish.(AU)

Ecological separation by ecomorphology and swimming performance between two congeneric fish species

The high diversity of freshwater fish species reflects a great morphological plasticity. Understanding the relationship between swimming capacity, morphology and habitat use may be important to predict the chances of finding a species at an anthropized environment. The swimming capacity and morphological aspects of two sympatric species of Characidium, and for which spatial segregation in different hydraulic habitats is known, were compared in this study. Twenty-one individuals of Characidium fasciatum Reinhardt, 1867 and 23 individuals of Characidium cf. zebra Eigenmann, 1909 were captured and used for the evaluation of the swimming capacity and ecomorphological attributes. The swimming capacity of each species was obtained by measuring critical and relative velocities. A total of 12 ecomorphological attributes correlated with habitat use and swimming characteristics were also compared. The Mann-Whitney mean test showed that the swimming capacity of C. fasciatum was greater than that of C. cf. zebra, and the standard length of the individuals explained 12.42% of the variation in their capacity to withstand water flow. Both species were morphologically distinct in the relative length of the caudal peduncle, ventral flattening index and the relative area of the pectoral fin. The relative area of the pectoral fin alone accounted for 16.71% of the differences in the ability to resist the water flow and which were not explained by body length. Our results showed that two species differed in the ecomorphological space and in their swimming capacity, supporting the hypothesis that the greater the hydrodynamism, the better a fish is able to withstand the water flow, and that this capacity is correlated with the morphological characteristics linked to the swimming activity of the fish.

Changes in trophic characteristics of two fish species of Astyanax (Teleostei: Characidae) in response to aquatic pollution

The trophic plasticity of most fish species of Astyanax Baird & Girard, 1854 in response to environmental changes and resource availability is high. This work evaluates the differences in the trophic characteristics of two congeneric species, Astyanax taeniatus (Jenyns, 1842) and Astyanax lacustris (Lütken, 1875), in Rio das Velhas Basin, which is highly impacted by the discharge of sewage from the Metropolitan Region of Belo Horizonte (MRBH). Eight sites were sampled and grouped into three regions: upper course (two sites upstream of the MRBH); middle course (three sites located in the middle portion of the Rio das Velhas, region with greater influence of the MRBH), and lower course (three sites downstream of the MRBH). Samples of fish and food resources were collected from all sites to obtain the isotopic composition of nitrogen (δ15N) and carbon (δ13C), and the stomach contents of the two species was analized. The most common items in the stomach of A. lacustris and A. taeniatus, respectively, were from plants and insects, followed by algae/periphyton (especially at the low course of Rio das Velhas). In contrast, stable isotope analyses indicated that algae (in polluted sites) and periphyton (in least-disturbed sites) were best assimilated both species. Both analyses indicated that the trophic niches of the two species overlap more in more polluted sites relative to less polluted sites. Astyanax taeniatus and A. lacustris only presented different isotopic composition of carbon and nitrogen in the upper course of the Rio das Velhas, probably in response to the greater diversity of food items consumed by each species. In the other regions, the species presented similar isotopic signatures, with δ15N and δ13C notably enriched in the most polluted regions (middle and low course)...

Changes in trophic characteristics of two fish species of Astyanax (Teleostei: Characidae) in response to aquatic pollution

The trophic plasticity of most fish species of Astyanax Baird & Girard, 1854 in response to environmental changes and resource availability is high. This work evaluates the differences in the trophic characteristics of two congeneric species, Astyanax taeniatus (Jenyns, 1842) and Astyanax lacustris (Lütken, 1875), in Rio das Velhas Basin, which is highly impacted by the discharge of sewage from the Metropolitan Region of Belo Horizonte (MRBH). Eight sites were sampled and grouped into three regions: upper course (two sites upstream of the MRBH); middle course (three sites located in the middle portion of the Rio das Velhas, region with greater influence of the MRBH), and lower course (three sites downstream of the MRBH). Samples of fish and food resources were collected from all sites to obtain the isotopic composition of nitrogen (δ15N) and carbon (δ13C), and the stomach contents of the two species was analized. The most common items in the stomach of A. lacustris and A. taeniatus, respectively, were from plants and insects, followed by algae/periphyton (especially at the low course of Rio das Velhas). In contrast, stable isotope analyses indicated that algae (in polluted sites) and periphyton (in least-disturbed sites) were best assimilated both species. Both analyses indicated that the trophic niches of the two species overlap more in more polluted sites relative to less polluted sites. Astyanax taeniatus and A. lacustris only presented different isotopic composition of carbon and nitrogen in the upper course of the Rio das Velhas, probably in response to the greater diversity of food items consumed by each species. In the other regions, the species presented similar isotopic signatures, with δ15N and δ13C notably enriched in the most polluted regions (middle and low course)...(AU)