RESUMO

Large predators have disproportionate effects on their underlying food webs. Thus, appropriately assigning trophic positions has important conservation implications both for the predators themselves and for their prey. Large-bodied predators are often referred to as apex predators, implying that they are many trophic levels above primary producers. However, theoretical considerations predict both higher and lower trophic position with increasing body size. Nitrogen stable isotope values (δ15N) are increasingly replacing stomach contents or behavioral observations to assess trophic position and it is often assumed that ontogenetic dietary shifts result in higher trophic positions. Intraspecific studies based on δ15N values found a positive relationship between size and inferred trophic position. Here, we use datasets of predatory vertebrate ectotherms (crocodilians, turtles, lizards and fishes) to show that, although there are positive intraspecific relationships between size and δ15N values, relationships between stomach-content-based trophic level (TPdiet) and size are undetectable or negative. As there is usually no single value for 15N trophic discrimination factor (TDF) applicable to a predator species or its prey, estimates of trophic position based on δ15N in ectotherm vertebrates with large size ranges, may be inaccurate and biased. We urge a reconsideration of the sole use of δ15N values to assess trophic position and encourage the combined use of isotopes and stomach contents to assess diet and trophic level.

Assuntos

RESUMO

Pollution by synthetic polymers is even more problematic to the environment when this material is fragmented into small portions, forming microplastics (MPs). We analyzed the contamination of ichthyofauna by MPs in an important river of the Atlantic Rainforest in regard to abundance, diversity of morphotypes, polymers, colors, and sizes of the synthetic particles in 20 species of fish. Fish were collected in November 2019 and in March 2020 in five sites along the Pomba River. Of the 101 fish analyzed, 49 (49%) presented MPs in at least one organ. Of the 20 species of fish collected 13 included individuals with at least one MP in their analyzed organs. The organs, trophic categories and feeding areas did not affect the general abundance of MPs types. Blue MPs were predominant, followed by the colors black, red, and white. MP fibers represented 91% of total MPs. Most MPs were between 2 and 3 mm in size. Polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polyvinylidene chloride "Nylon" (PVDC), and high-density polyethylene (HDPE) were detected in the fishes. The exposure of the fish species to MPs was associated mainly with individual size and species-specific aspects, regardless of ecological traits. Considering that 55% of the fish species studied are consumed by humans, it is necessary to study the potential impact of MP ingestion on human health and to understand to what extent we may be consuming both plastic particles and contaminants that are adsorbed to MPs.

Assuntos

RESUMO

Rivers are known for carrying out a fundamental role in the transportation of human debris from continental areas to the marine environment and have been identified as hotspots for plastic pollution. We characterized microplastics (MPs) along confluence areas in the Paraíba do Sul River basin, the biggest river in southeastern Brazil. This water body crosses highly industrialized areas, with the highest population density, and the major water demand in South America. Considering the important ecological function of this extensive watershed and the implications of MP pollution, we evaluate the spatial variation of MP concentration in the confluence areas and upstream from the confluence. Samples were taken from the superficial layer of the water column in February and June 2022, using manta net with 300 µm mesh size. A total of 19 categories and 2870 plastic particles were determined. The confluences areas of rivers showed the highest concentration of MPs, highlighting the confluences of the Paraiba do Sul and Muriaé rivers (0.71 ± 0.25 MP/m3), followed by Paraíba do Sul and Dois Rios rivers (0.42 ± 0.23 MP/m3) and Paraíba do Sul and Pomba rivers (0.38 ± 0.14 MP/m3). Black fibers were the main category, followed by blue fibers and blue fragments. The MPs in the surface waters of Paraíba do Sul River is significantly influenced by the sampling points spatiality. This result corroborates other studies around the world and reinforces the argument that affluents are important sources for the introduction of MPs in larger rivers. Nevertheless, our results provide a better understanding of the different contributing factors and occurrence of MPs in river basins.

Assuntos

RESUMO

This study aimed to estimate the parameters of length-weight relationship, sex ratio, and diet of three freshwater fish species that inhabit streams in the Pomba River basin (Rio de Janeiro, Brazil). Fishes were sampled with seine nets (2.0 × 1.20 m, 2 mm mesh size) and dip nets (0.46 × 0.33 m, 2 mm mesh size) from October to December 2018. Measurements were taken for total length (TL - 0.1 cm precision) and total weight (TW - 0.01 g precision). Growth model parameters were estimated. This study provides new length-weight relationship data for Deuterodon intermedius (Eigenmann, 1908), Australoheros paraibae Ottoni & Costa, 2008, and Hypostomus punctatus Valenciennes, 1840. All of them ingested a wide variety of food items, including plant material like algae, animal material such as terrestrial and aquatic insects, and undefined matter such as detritus or mud. The three species showed a higher number of females. Our study provides basic information for functional diversity studies, as well as for future investigations associated with the evaluation of anthropic impacts, either occasional or chronic, on the fish assemblage structure of the Pomba River basin.(AU)

Assuntos

RESUMO

The Machado River is the main tributary of the Madeira River in the state of Rondônia, a region that has been impacted by deforestation, livestock, urban development, alluvial gold mining and urban and industrial effluents that likely contribute to the introduction of mercury (Hg) in the aquatic system. We aimed to determine the concentrations of total Hg (THg) in muscle and liver of Plagioscion squamosissimus, a main fishing resource in the region. Fish were sampled for two years at five sites, along a 90-km stretch of the middle Machado River. THg concentrations were analyzed in 64 muscle and 54 liver samples by cold vapor atomic absorption spectrophotometry (FIMS-400). THg levels were related with fish size and sex and with periods of the hydrological cycle. THg concentrations in both organs were positively and significantly related with fish body size. There was no significant variation in THg among periods of the hydrological cycle. Mean THg concentrations in muscle (1.09 ± 0.72 mg kg-1) and liver (1.28 ± 1.23 mg kg-1) were higher than the limit established by the WHO. Our results suggest that residual mercury from former alluvial gold extraction and lixiviation of mercury naturally occurring in the soil due to large-scale deforestaion is accumulating in the aquatic food chain in the Machado River. We conclude that it is necessary to monitor the levels of mercury in commercially important fish species in the region.(AU)

O Rio Machado é o principal afluente do Rio Madeira no estado de Rondônia, uma região impactada por desmatamento, pecuária, desenvolvimento urbano, mineração de ouro e efluentes urbanos e industriais, que provavelmente contribuem para a introdução de mercúrio (Hg) no sistema aquático. Nosso objetivo foi determinar as concentrações de Hg total (THg) em músculo e fígado de Plagioscion squamosissimus, um importante recurso pesqueiro na região. Os peixes foram amostrados durante dois anos em cinco locais ao longo de 90 km no médio Rio Machado. As concentrações de THg foram analisadas em 64 amostras de músculos e 54 de fígado por espectrofotometria de absorção atômica com vapor frio (FIMS-400). As concentrações de mercúrio foram relacionadas ao tamanho e sexo dos peixes, e com períodos do ciclo hidrológico. As concentrações de THg em ambos os órgãos foram relacionadas positiva e significativamente com o tamanho corporal dos peixes. Não houve variação significativa do THg entre os períodos do ciclo hidrológico. As concentrações médias de THg no músculo (1,09 ± 0,72 mg kg-1) e no fígado (1,28 ± 1,23 mg kg-1) foram superiores ao limite estabelecido pela OMS. Os resultados sugerem que o mercúrio residual da extração de ouro e lixiviação de mercúrio que ocorre naturalmente no solo desmatado está se acumulando na cadeia alimentar aquática do Rio Machado. Concluímos que é necessário monitorar os níveis de mercúrio em espécies de peixes comerciais na região.(AU)

Assuntos

RESUMO

We analyzed the seasonal variation in the diet, trophic niche breadth (Levins index), the partitioning of food resources (Pianka's symmetric index) and trophic level (weighed average of trophic level of each prey determined in FishBase and SeaLifeBase platform) of Plagioscion squamosissimus (Heckel, 1840) and Hydrolycus scomberoides (Cuvier, 1819) in the Machado River, Rondônia, Brazil. Fish samplings were conducted bimonthly from June 2013 to May 2015 in five sites, using eight sets of gillnets. The occurrence frequency and volumetric frequency were used to quantify the food items. We analyzed the stomach contents of 283 individuals, 134 of H. scomberoides and 149 of P. squamosissimus. Fish were the most consumed food item by both piscivorous species. However, H. scomberoides mostly ingested pelagic fish (e.g. Characiformes fishes and Prochilodus nigricas Spix & Agassiz, 1829), while P. squamosissimus mostly consumed benthic fish [e.g. Pimelodus blochii Valenciennes, 1840 and Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides presented the trophic level 3.55 for both periods analyzed, while P. squamosissimus 4.01 in the flood period and 3.82 in the drought period. Seasonal variations in the diet of H. scomberoides and P. squamosissimus were observed (PERMANOVA). Specifically, P. squamosissimus consumed mainly "Siluriformes" fishes and P. blochii in the drought period. The trophic niche breadth of P. squamosissimus was greater than that of H. scomberoides in the flood period. The species P. squamosissimus and H. scomberoides had low (0.35) food niche overlap in both seasons analysed. The data indicated that P. squamosissimus has a generalist feeding habit, while H. scomberoides is specialized in prey selection. The overlap of food niche between the species in both periods of the hydrological cycle was low, indicating that niche partitioning was probably the main mechanism of coexistence of these species, with little relationship with variations of the hydrological cycle.

Nós analisamos a variação sazonal na dieta, a amplitude do nicho trófico (Índice de Levins), a partição dos recursos alimentares (Índice simétrico de Pianka) e o nível trófico (média do nível trófico de cada presa determinada pela plataforma FishBase e SeaLifeBase) de Plagioscion squamosissimus (Heckel, 1840) e Hydrolycus scomberoides (Cuvier, 1819) no rio Machado, Rondônia, Brasil. As amostragens de peixes foram realizadas bimestralmente de junho de 2013 a maio de 2015 em cinco locais, utilizando oito conjuntos de redes de emalhar. A frequência de ocorrência e a frequência volumétrica foram utilizados para quantificar os itens alimentares. Analisamos o conteúdo estomacal de 283 indivíduos, 134 de H. scomberoides e 149 de P. squamosissimus. Peixes foram o item alimentar mais consumido pelas duas espécies piscívoras. No entanto, H. scomberoides ingeriu principalmente peixes pelágicos (ex. peixes Characiformes e Prochilodus nigricas Spix & Agassiz, 1829), enquanto P. squamosissimus consumiu principalmente peixes bentônicos [ex. Pimelodus blochii Valenciennes, 1840 e Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides apresentou nível trófico de 3,55 para ambos os períodos analisados, enquanto para P. squamosissimus o nível trófico foi de 4,01 no período da cheia e 3,82 no período de seca. Variações sazonais na dieta de H. scomberoides e P. squamosissimus foram observadas (PERMANOVA). Especificamente, P. squamosissimus consumiu principalmente peixes "Siluriformes" e P. blochii no período de seca. A largura do nicho trófico de P. squamosissimus foi maior que a de H. scomberoides no período da cheia. Plagioscion squamosissimus e H. scomberoides apresentaram baixa (0,35) sobreposição de nicho alimentar nas duas estações analisadas. Os dados indicaram que P. squamosissimus tem hábito alimentar generalista, enquanto H. scomberoides é especializado na seleção de presas. A sobreposição de nicho alimentar entre as espécies em ambos os períodos do ciclo hidrológico foi baixa, indicando que a partição de nicho foi provavelmente o principal mecanismo de coexistência dessas espécies, com pouca relação com as variações do ciclo hidrológico.

Assuntos

RESUMO

ABSTRACT We analyzed the seasonal variation in the diet, trophic niche breadth (Levins index), the partitioning of food resources (Piankas symmetric index) and trophic level (weighed average of trophic level of each prey determined in FishBase and SeaLifeBase platform) of Plagioscion squamosissimus (Heckel, 1840) and Hydrolycus scomberoides (Cuvier, 1819) in the Machado River, Rondônia, Brazil. Fish samplings were conducted bimonthly from June 2013 to May 2015 in five sites, using eight sets of gillnets. The occurrence frequency and volumetric frequency were used to quantify the food items. We analyzed the stomach contents of 283 individuals, 134 of H. scomberoides and 149 of P. squamosissimus. Fish were the most consumed food item by both piscivorous species. However, H. scomberoides mostly ingested pelagic fish (e.g. Characiformes fishes and Prochilodus nigricas Spix & Agassiz, 1829), while P. squamosissimus mostly consumed benthic fish [e.g. Pimelodus blochii Valenciennes, 1840 and Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides presented the trophic level 3.55 for both periods analyzed, while P. squamosissimus 4.01 in the flood period and 3.82 in the drought period. Seasonal variations in the diet of H. scomberoides and P. squamosissimus were observed (PERMANOVA). Specifically, P. squamosissimus consumed mainly Siluriformes fishes and P. blochii in the drought period. The trophic niche breadth of P. squamosissimus was greater than that of H. scomberoides in the flood period. The species P. squamosissimus and H. scomberoides had low (0.35) food niche overlap in both seasons analysed. The data indicated that P. squamosissimus has a generalist feeding habit, while H. scomberoides is specialized in prey selection. The overlap of food niche between the species in both periods of the hydrological cycle was low, indicating that niche partitioning was probably the main mechanism of coexistence of these species, with little relationship with variations of the hydrological cycle.

RESUMO Nós analisamos a variação sazonal na dieta, a amplitude do nicho trófico (Índice de Levins), a partição dos recursos alimentares (Índice simétrico de Pianka) e o nível trófico (média do nível trófico de cada presa determinada pela plataforma FishBase e SeaLifeBase) de Plagioscion squamosissimus (Heckel, 1840) e Hydrolycus scomberoides (Cuvier, 1819) no rio Machado, Rondônia, Brasil. As amostragens de peixes foram realizadas bimestralmente de junho de 2013 a maio de 2015 em cinco locais, utilizando oito conjuntos de redes de emalhar. A frequência de ocorrência e a frequência volumétrica foram utilizados para quantificar os itens alimentares. Analisamos o conteúdo estomacal de 283 indivíduos, 134 de H. scomberoides e 149 de P. squamosissimus. Peixes foram o item alimentar mais consumido pelas duas espécies piscívoras. No entanto, H. scomberoides ingeriu principalmente peixes pelágicos (ex. peixes Characiformes e Prochilodus nigricas Spix & Agassiz, 1829), enquanto P. squamosissimus consumiu principalmente peixes bentônicos [ex. Pimelodus blochii Valenciennes, 1840 e Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides apresentou nível trófico de 3,55 para ambos os períodos analisados, enquanto para P. squamosissimus o nível trófico foi de 4,01 no período da cheia e 3,82 no período de seca. Variações sazonais na dieta de H. scomberoides e P. squamosissimus foram observadas (PERMANOVA). Especificamente, P. squamosissimus consumiu principalmente peixes Siluriformes e P. blochii no período de seca. A largura do nicho trófico de P. squamosissimus foi maior que a de H. scomberoides no período da cheia. Plagioscion squamosissimus e H. scomberoides apresentaram baixa (0,35) sobreposição de nicho alimentar nas duas estações analisadas. Os dados indicaram que P. squamosissimus tem hábito alimentar generalista, enquanto H. scomberoides é especializado na seleção de presas. A sobreposição de nicho alimentar entre as espécies em ambos os períodos do ciclo hidrológico foi baixa, indicando que a partição de nicho foi provavelmente o principal mecanismo de coexistência dessas espécies, com pouca relação com as variações do ciclo hidrológico.

RESUMO

Estudos sobre a estrutura trófica de peixes dão informações sobre autoecologia espécies e seu papel no ecossistema. Os objetivos deste estudo foram caracterizar a dieta Serrapinnus notomelas em igarapés da bacia do rio Machado e avaliar o efeito da sazonalidade das chuvas. Os peixes foram coletados bimestralmente de julho 2013 a maio de 2014, com redes de arrasto e redes de mão. O comprimento de cada espécime foi medido para identificar a categoria das classes. Também foram medidos o grau de repleção e o volume de cada item ingerido, e estes dados foram combinadas para se obter um índice alimentar. Foram utilizados uma ANOVA e Kruskal-Wallis para diferenças entre classes de comprimento e graus de repleção, teste de qui-quadrado para detectar diferenças sazonais na origem dos alimentos e análise de escalonamento multidimensional não-métrico para examinar variação temporal na dieta. Nós encontramos que a maioria dos indivíduos eram maiores que 20 mm, apresentando distribuição polimodal. Para ambas as estações a maioria dos estômagos apresentaram-se cheios. Serrapinnus notomelas ingeriu itens vegetais e animais. Observamos maior consumo de macrófitas aquáticas e algas, sugerindo comportamento alimentar onívoro com tendência a herbivoria. Itens de origem vegetal e autóctone foram mais consumidos que os demais itens em ambas as estações, e o consumo de itens animais e itens autóctones variou entre as estações. Estes resultados reforçam a ideia de que S. notomelas apresenta plasticidade trófica entre as estações.(AU)

Assuntos

RESUMO

Studies on the trophic structure of fish give information on species autoecology and their role in the ecosystem. The aims of this study were to characterize the diet of Serrapinnus notomelas in small streams of the River Machado basin and to assess the effect of rainfall seasonality. Fish were collected bimonthly from July 2013 to May 2014 with seine nets and hand nets. The length of each specimen was measured to identify category classes. There were also measured the fullness index and volume of each ingested item, and these data were combined to obtain an alimentary index. We used ANOVA and Kruskal-Wallis to test for differences between length classes and fullness index, Chi-squared tests to detect seasonal differences in origin of food items and non-metric multidimensional scaling analysis to examine temporal variation in diet. We found that most of the specimens were longer than 20 mm, showing a polymodal distribution. In both seasons stomachs of most fish were full. Serrapinnus notomelas feeds on items of plant and animal origin. A higher consumption of aquatic macrophytes and algae was observed, suggesting omnivorous feeding behavior with a tendency to herbivory. Items of plant and autochthonous origin were consumed more than other items in both seasons, and consumption of animal and autochthonous items varied between seasons. These results reinforce the idea that S. notomelas show trophic plasticity between seasons.(AU)

Estudos sobre a estrutura trófica de peixes dão informações sobre autoecologia espécies e seu papel no ecossistema. Os objetivos deste estudo foram caracterizar a dieta Serrapinnus notomelas em igarapés da bacia do rio Machado e avaliar o efeito da sazonalidade das chuvas. Os peixes foram coletados bimestralmente de julho 2013 a maio de 2014, com redes de arrasto e redes de mão. O comprimento de cada espécime foi medido para identificar a categoria das classes. Também foram medidos o grau de repleção e o volume de cada item ingerido, e estes dados foram combinadas para se obter um índice alimentar. Foram utilizados uma ANOVA e Kruskal-Wallis para diferenças entre classes de comprimento e graus de repleção, teste de qui-quadrado para detectar diferenças sazonais na origem dos alimentos e análise de escalonamento multidimensional não-métrico para examinar variação temporal na dieta. Nós encontramos que a maioria dos indivíduos eram maiores que 20 mm, apresentando distribuição polimodal. Para ambas as estações a maioria dos estômagos apresentaram-se cheios. Serrapinnus notomelas ingeriu itens vegetais e animais. Observamos maior consumo de macrófitas aquáticas e algas, sugerindo comportamento alimentar onívoro com tendência a herbivoria. Itens de origem vegetal e autóctone foram mais consumidos que os demais itens em ambas as estações, e o consumo de itens animais e itens autóctones variou entre as estações. Estes resultados reforçam a ideia de que S. notomelas apresenta plasticidade trófica entre as estações.(AU)

Assuntos

RESUMO

Igarapés are Amazonian streams that are extremely susceptible to environmental changes. Due to the rapidly occurring riparian land use changes, and the several impacts these may have on fish assemblages, it is highly valuable to describe and understand the current relationships between these assemblages and the local environmental conditions, especially in barely know areas. In this research, we studied the taxonomic composition and fish assemblage attributes variation in three streams with different riparian conservation conditions: forest, intermediate and pasture. Samplings were performed every two months from October 2011 to September 2012, in three 1st order streams in the Machado River Basin, Rondônia. Fish were collected using trawls (seine net with a mesh size of 2 mm) and dip nets (2 mm mesh) along the entire stretch; the obtained samples were preserved and identified per site type. A total of 2 141 fish specimens belonging to 59 species, 17 families and five orders were recorded. Unlike the intermediate and pasture streams, the forest stream showed a high richness and low abundance. The forested stream exhibited the highest diversity and evenness value, and had low dominance, unlike the other streams. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that assemblage composition was significantly explained by the environmental variables such as: depth, water velocity, pteridophytes and grasses, but not by spatial predictors. The non-metric multidimensional scaling (NMDS) analysis showed that intermediate and pasture streams separated from the forested stream. We concluded that both, the stream environmental variables and fish assemblage attributes were influenced by the different conservation status and land cover. Given the influence of regional processes, which have a pervasive role in local fish assemblages, land use at the watershed scale is important, especially to explain the higher richness and diversity found in forested streams.

Assuntos

RESUMO

Abstract: This work assessed freshwater fishes collected at 12 stations located along the Tarumã River, middle Machado River, Madeira River basin. The fieldwork took place in May and September 2015 during the high and low water seasons, respectively. We gathered 1,482 specimens representing seven orders, 30 families, 54 genera and 74 species using seine, gill, and hand nets. The family Characidae was the most representative, exhibiting the highest number of species captured. The species with the greatest abundance were Hemigrammus vorderwinkleri, Hyphessobrycon bentosi, Hemigrammus cf. bellottii, Bryconella pallidifrons, and Apistogramma resticulosa. Two species that remained unidentified are probably a new species. This study represents the third fish survey totally conducted at a Conservation Unit in the Rondônia State, and will certainly provide valuable information for future investigations on biodiversity conservation in the Machado River.

Resumo: Este trabalho avaliou os peixes de água doce coletados em 12 estações localizadas ao longo do rio Tarumã, médio rio Machado, bacia do rio Madeira. O trabalho de campo ocorreu em maio e em setembro de 2015 durante os períodos de cheia e seca, respectivamente. Um total de 1.482 exemplares, sete ordens, 30 famílias, 54 gêneros e 74 espécies foram amostrados com malhadeiras, picaré e puça. Characidae foi a família com maior número de espécies capturadas. As espécies com maior abundância foram Hemigrammus vorderwinkleri, Hyphessobrycon bentosi, Hemigrammus cf. bellottii, Bryconella pallidifrons e Apistogramma resticulosa. Duas espécies não foram identificadas e provavelmente podem ser novas espécies. Este estudo representa a terceira pesquisa de peixes totalmente realizada em uma Unidade de Conservação no Estado Rondônia, e certamente fornecerá informações valiosas para futuros estudos sobre a conservação da biodiversidade do rio Machado.

RESUMO

Determining the significance of biotic and abiotic factors in the structuring of fish assemblages in freshwater environments is an important question in ecology, particularly in view of environmental changes caused by man. In this paper we sought to identify the factors responsible for the composition and abundance of fish species collected with gill nets in six locations near ports in forest clearance areas opened up for oil and natural gas exploration (Petrobras Pedro Moura Base) in the Urucu River, during drought and flood cycles. In all, 923 individuals from 23 families and 82 species were collected, totalling a biomass of 182,244 g. The most abundant species during the flood season were Bryconops alburnoides (Kner, 1858) and Dianema urostriatum (Miranda Ribeiro, 1912); in the drought season, the predominant species were Osteoglossum bicirrhosum (Cuvier, 1829) and Serrasalmus rhombeus (Linnaeus, 1766). The species with the greatest biomass during the flood season were Pellona castelnaeana (Valenciennes, 1847), S. rhombeus and Pellona flavipinis (Valenciennes, 1847). During the drought season, the predominant species was O. bicirrhosum. When both periods were analysed together, electrical conductivity, water transparency and dissolved oxygen were the most important factors. The species Hemisorubim platyrhynchos (Valenciennes, 1840), O. bicirrhosum, Chaetobranchus flavenscens Heckel, 1840, Geophagus proximus (Castelnau, 1855) were strongly related to high values of conductivity, pH and water current velocity during the drought season, as well as Serrasalmus altispinis Merckx, Jégu & Santos, 2000, Triportheus albus Cope, 1872, Triportheus angulatus (Spix & Agassiz, 1829) and Brycon melanopterus (Cope, 1872) that were associated with less depth and width in the drought season whereas P. castelnaeana, D. urostriatum, Rhytiodus argenteofuscus Kner, 1858 and Sorubim lima (Bloch & Schneider, 1801) were mainly associated with high transparency and dissolved oxygen during the flood season.

Assuntos

RESUMO

Trophic relationships in fish communities are affected by the availability of resources, which in turn is affected by spatial and temporal variations throughout the year. The aims of this study were to characterize the diet of A. tetramerus in a streamlet in the north of Brazil and compare its composition in different hydrological seasons (wet and dry seasons). Collections were performed every two months from October 2011 to September 2012 with the aid of seine nets, hand net and fishing traps in the streamlet located in the Machado River drainage basin in the Rondônia state. Most of the specimens collected were quite small (<40 mm) and had empty stomachs. Our results showed that A. tetramerus feeds on a wide variety of items of plant origin, such as algae, seeds and leaves, as well as items of animal origin, including bryozoans, crustaceans, fish scales, terrestrial insects and detritus. The data also indicated higher consumption of aquatic insects than other food items, suggesting a primarily insect-based diet. Items of plant and allochthonous origin were consumed more in the wet season than in the dry season, but there were no seasonal differences in the consumption of animal and autochthonous items.

Relações tróficas das comunidades de peixes são afetadas por variações espaciais e temporais, que alteraram a disponibilidade de recursos ao longo do ano. Os objetivos deste estudo foram caracterizar a dieta de A. tetramerus no igarapé estudado, bem como comparar se a composição dos itens da dieta desta espécie dependem da estação hidrológica (período chuvoso e seco). As coletas foram realizadas bimestralmente, de Outubro de 2011 a Setembro de 2012, com auxílio de picaré, puçá e covos em um igarapé localizado na bacia do rio Machado no estado de Rondônia. A maioria dos espécimes eram pequenos (<40 mm) e tinham estômago vazio. Observou-se que A. tetramerus se alimenta de uma grande variedade de itens de origem vegetal, como algas, sementes e folhas; e de itens de origem animal como: briozoários, crustáceos, escamas, insetos terrestres e detritos. Constatou-se que há maior consumo de insetos aquáticos, o que sugere uma dieta insetívora. Itens de origem vegetal e alóctones foram mais consumidos na estação chuvosa do que na estação seca. Não houve diferença na composição da dieta dos peixes entre as estações de seca e chuva.

Assuntos

RESUMO

Trophic relationships in fish communities are affected by the availability of resources, which in turn is affected by spatial and temporal variations throughout the year. The aims of this study were to characterize the diet of A. tetramerus in a streamlet in the north of Brazil and compare its composition in different hydrological seasons (wet and dry seasons). Collections were performed every two months from October 2011 to September 2012 with the aid of seine nets, hand net and fishing traps in the streamlet located in the Machado River drainage basin in the Rondônia state. Most of the specimens collected were quite small (<40 mm) and had empty stomachs. Our results showed that A. tetramerus feeds on a wide variety of items of plant origin, such as algae, seeds and leaves, as well as items of animal origin, including bryozoans, crustaceans, fish scales, terrestrial insects and detritus. The data also indicated higher consumption of aquatic insects than other food items, suggesting a primarily insect-based diet. Items of plant and allochthonous origin were consumed more in the wet season than in the dry season, but there were no seasonal differences in the consumption of animal and autochthonous items.(AU)

Relações tróficas das comunidades de peixes são afetadas por variações espaciais e temporais, que alteraram a disponibilidade de recursos ao longo do ano. Os objetivos deste estudo foram caracterizar a dieta de A. tetramerus no igarapé estudado, bem como comparar se a composição dos itens da dieta desta espécie dependem da estação hidrológica (período chuvoso e seco). As coletas foram realizadas bimestralmente, de Outubro de 2011 a Setembro de 2012, com auxílio de picaré, puçá e covos em um igarapé localizado na bacia do rio Machado no estado de Rondônia. A maioria dos espécimes eram pequenos (<40 mm) e tinham estômago vazio. Observou-se que A. tetramerus se alimenta de uma grande variedade de itens de origem vegetal, como algas, sementes e folhas; e de itens de origem animal como: briozoários, crustáceos, escamas, insetos terrestres e detritos. Constatou-se que há maior consumo de insetos aquáticos, o que sugere uma dieta insetívora. Itens de origem vegetal e alóctones foram mais consumidos na estação chuvosa do que na estação seca. Não houve diferença na composição da dieta dos peixes entre as estações de seca e chuva.(AU)

Assuntos

RESUMO

Determining the significance of biotic and abiotic factors in the structuring of fish assemblages in freshwater environments is an important question in ecology, particularly in view of environmental changes caused by man. In this paper we sought to identify the factors responsible for the composition and abundance of fish species collected with gill nets in six locations near ports in forest clearance areas opened up for oil and natural gas exploration (Petrobras Pedro Moura Base) in the Urucu River, during drought and flood cycles. In all, 923 individuals from 23 families and 82 species were collected, totalling a biomass of 182,244 g. The most abundant species during the flood season were Bryconops alburnoides (Kner, 1858) and Dianema urostriatum (Miranda Ribeiro, 1912); in the drought season, the predominant species were Osteoglossum bicirrhosum (Cuvier, 1829) and Serrasalmus rhombeus (Linnaeus, 1766). The species with the greatest biomass during the flood season were Pellona castelnaeana (Valenciennes, 1847), S. rhombeus and Pellona flavipinis (Valenciennes, 1847). During the drought season, the predominant species was O. bicirrhosum. When both periods were analysed together, electrical conductivity, water transparency and dissolved oxygen were the most important factors. The species Hemisorubim platyrhynchos (Valenciennes, 1840), O. bicirrhosum, Chaetobranchus flavenscens Heckel, 1840, Geophagus proximus (Castelnau, 1855) were strongly related to high values of conductivity, pH and water current velocity during the drought season, as well as Serrasalmus altispinis Merckx, Jégu & Santos, 2000, Triportheus albus Cope, 1872, Triportheus angulatus (Spix & Agassiz, 1829) and Brycon melanopterus (Cope, 1872) that were associated with less depth and width in the drought season whereas P. castelnaeana, D. urostriatum, Rhytiodus argenteofuscus Kner, 1858 and Sorubim lima (Bloch & Schneider, 1801) were mainly associated with high transparency and dissolved oxygen during the flood season.(AU)

Assuntos