Resumo Objetivo: Este estudo avaliou a estrutura trófica de uma assembleia de peixes ao longo do gradiente longitudinal de um riacho rural de primeira ordem. Métodos As amostragens foram realizadas em dezembro de 2007, setembro de 2008 e março de 2009, em três pontos do riacho Itiz (montante, meio e foz), através da técnica de pesca elétrica. Foram amostrados 1.255 indivíduos referentes a 18 espécies. A categorização das guildas tróficas foi baseada em dados de conteúdo estomacal de 1.096 indivíduos, analisados de acordo com o método volumétrico, exceto para quatro espécies, que foram classificadas de acordo com a literatura. Para testar a hipótese de que existem diferenças na riqueza, abundância e biomassa de guildas tróficas no sentido cabeceira-foz, foi realizada análise estatística não-paramétrica sobre os dados da dieta. Calculou-se também, a amplitude de nicho trófico (Levins's index) para cada guilda. Para sumarizar os dados de composição e abundância das guildas ao longo do gradiente longitudinal, foi aplicado uma análise de escalonamento multidimensional não-métrico (NMDS). Resultados Foram registradas sete guildas: herbívora, detritívora, insetívora aquática, insetívora terrestre, invertívora, onívora e piscívora, esta última sendo exclusiva para os trechos da cabeceira e meio do riacho. A guilda onívora não foi registrada na cabeceira. Através da análise PERMANOVA verificou-se que a riqueza de espécies das guildas mais especializadas (detritívora e insetívora terrestre) e da generalista invertívora, aumentou, enquanto as guildas menos especializadas (insetívora aquática e herbívora), diminuiu significativamente em direção cabeceira-foz. Exceto pelo aumento não esperado de insetívora terrestre e diminuição de herbívora rio abaixo, o escalonamento multidimensional não-métrico (NMDS) identificou variações longitudinais na abundância e biomassa das guildas que corroboram os padrões gerais de distribuição das guildas tróficas dos peixes ao longo de gradientes ambientais. Conclusão Estes resultados sugerem que a influência das condições ambientais do entorno do riacho (particularidades locais) também contribui para a formação dos padrões de guildas tróficas observados ao longo do gradiente longitudinal.

Abstract Aim: This study evaluated the trophic structure of the fish assemblage along the longitudinal gradient of a first-order rural stream. Methods Fish were sampled by electrofishing technique in December 2007, September 2008 and March 2009, at three stretch of the Itiz stream (headwater, middle and mouth). We sampled 1,255 individuals relating to 18 species. The categorization of trophic guilds was based on stomach content data of 1,096 individuals, analyzed according to the volumetric method, except for four species, which were classified according to the literature. To test the hypothesis of differences in the richness, abundance and biomass of trophic guilds along the headwater-mouth gradient, it was performed non-parametric statistical analysis of the dietary data. Was also calculated, the amplitude of trophic niche (Levins's index) for each guild. To summarize the composition and abundance of the trophic guilds along the longitudinal gradient, we applied a non-metric multidimensional scaling (NMDS). Results We registered seven guilds: herbivorous, detritivorous, aquatic insectivorous, terrestrial insectivorous, invertivorous, omnivorous and piscivorous, the latter was exclusive to headwater and middle stretches. The omnivorous guild was not recorded in the headwater. Through PERMANOVA analysis it was found that the species richness of more specialized guilds (detritivorous and insectivorous terrestrial) and of generalist invertivorous increased, while less specialized guilds like aquatic insectivorous and herbivorous, decrease significantly in headwater-mouth direction. Except by the non-expected increase of insectivorous terrestrial and decrease of herbivorous downstream, the non-metric multidimensional scaling (NMDS) identified longitudinal variations in abundance and biomass of the guilds that agree with general patterns of fish guilds distribution along environmental gradients. Conclusion These results suggest that the influence of environmental conditions around the stream (local particularities) also contributed to the formation of the observed patterns of trophic guilds along its longitudinal gradient.

Spatial and temporal variations in food supply play a crucial role in the determination of the patterns of food use by fish species. This study evaluated spatial and temporal variations in food utilization by small fish species of the Verde River, Upper Paraná River Basin, state of Mato Grosso do Sul, Brazil. Samplings were conducted in the rainy and dry periods, from November 2010 to August 2012, using trawls, cast nets and gillnets, in nine sampling sites grouped into three biotopes: upstream and downstream of the Branca Waterfall, and tributary. The stomach contents of 3,263 individuals of 12 small species were examined according to the volumetric method. Altogether, 31 food items were identified. Overall seed consumption was greater in the rainy period, and the consumption of terrestrial plants was greater in the dry period. Hymenoptera was an important item in the diet, but the proportions in the consumption of this item was different between biotopes and periods. The consumption of Coleoptera and Isoptera was expressive only downstream of the Branca Waterfall in the rainy period, and aquatic plant was mostly consumed in the tributary in the dry period. Significant differences were detected in the diet composition between biotopes, hydrological periods and also the interaction between these two factors. Allochthonous resources were clearly the most consumed by the species in all biotopes, especially during the rainy period. The dietary overlap between species, although showing significant spatial and temporal differences, was low (0.4) for about 60% of species pairs. Thus, it is concluded that spatial and temporal changes in the utilization of food resources by small fish were related to physiographic differences of the channel and the surroundings, which contributed to the significance of seasonal changes in the diet, also reflecting the low dietary overlap between species.

In the present study, we describe the diets of the fish assemblages in two streams in the Maringá region of Paraná that are under the influence of different anthropic impacts. We also evaluate how the origin and use of food resources varies temporally and spatially and how the trophic organization of the fish assemblages differs between the two streams. Fish were collected every two months from October 2006 to October 2007 using sieves, seining and closing nets along two 50 m stretches of each stream. We used the volumetric method to analyze the stomach contents of 599 fish belonging to 15 species. We then employed ANOSIM, SIMPER, NMDS and cluster analyses (using the Bray-Curtis index) to examine how different factors (species, stream, sampling site and season) influenced the diets of the assemblages. The dietary analysis revealed a total of 21 types of items consumed, with the most common being detritus and immature Diptera. Spatial factors resulted in differences in diets between the two streams, with detritus representing the material consumed most often in the Morangueiro stream and immature Diptera being the most consumed item in the Queçaba stream. SIMPER analysis indicated a 76.33% dissimilarity between species' diets during the dry and rainy seasons, with detritus, immature Diptera and testate amoebae making the greatest contributions to this differentiation. In the Morangueiro stream, three trophic guilds were found: detritivorous, detritivorous/aquatic insectivorous, and aquatic insectivorous. In Queçaba stream, six trophic guilds were present: detritivorous, benthophagous, aquatic insectivorous, terrestrial insectivorous, herbivorous and carnivorous. Autochthonous items were generally the items most consumed by species, in particularly in the Queçaba stream. In the Morangueiro stream, food items of indeterminate origin were more relevant. The differences in the diets of fish species between the two streams support the conclusion that urbanization causes the disruption of aquatic environments and trophic organization.

Este estudo abordou a ecologia alimentar da ictiofauna de um riacho de primeira ordem situado em área rural. Os objetivos foram verificar a influência dos fatores interespecíficos, sazonais e espaciais sobre a dieta, avaliar a sobreposição alimentar, além de determinar os recursos alimentares predominantes. As amostragens foram realizadas em dezembro/2007, setembro/ 2008 e março/2009, em três pontos do riacho Itiz (montante, intermediário e foz) com extensões de 50 m, através de pesca elétrica. Foram analisados 1102 conteúdos estomacais referentes a 14 espécies de acordo com o método volumétrico. De forma geral observou-se que a maior contribuição na dieta das espécies foi de recursos alóctones. Astyanax aff. fasciatus, Astyanax aff. paranae, Astyanax bockmanni, Bryconamericus aff. iheringi, consumiram maior proporção de vegetal e Bryconamericus stramineus predominantemente Hymenoptera. Cetopsorhamdia iheringi, Characidium aff. zebra, Imparfinis schubarti e Trichomycterus sp. tiveram sua dieta baseada em insetos aquáticos, especialmente formas imaturas de Trichoptera, Ephemeroptera, Plecoptera e Diptera. Hypostomus ancistroides, Hisonotus sp., Poecilia reticulata e Rineloricaria aff. pentamaculata exploraram principalmente detrito, enquanto Rhamdia quelen usou uma variedade de itens, com predomínio de insetos terrestres. A análise de Correspondência com Remoção do Efeito do Arco (DCA) demonstrou uma segregação evidente entre as espécies com morfologia e táticas alimentares distintas. O Procedimento Permutacional de Multiresposta (MRPP) além de corroborar essa diferenciação, também mostrou variações espaciais e temporais significativas na composição da dieta das espécies, e o Método de Valor Indicador (IndVal) apontou os principais itens que contribuíram para essas diferenças. A sobreposição alimentar entre as espécies foi baixa (< 0.4) para cerca de 78% dos pares e a média não variou significativamente entre os locais, assim como entre os períodos hidrológicos dentro de cada ponto. De acordo com o modelo nulo do índice de Pianka, os valores de sobreposição alimentar foram significativamente maiores do que o esperado ao acaso, apresentando evidência de partição de recursos. Isto se deve à disponibilidade de itens alóctones, evidenciando a importância da mata ciliar como fonte desses recursos para a manutenção da ictiofauna do riacho estudado.

This study addressed the feeding ecology of fish fauna from a first-order stream located in a rural area. The purposes were to evaluate the influence of interspecific, seasonal and spatial factors on the diet, examine the dietary overlap, and determine the predominant food sources. Sampling was conducted in December 2007, September 2008, and March 2009, in three 50-m stretches of Itiz stream (upstream, intermediate, and downstream), through electrofishing. A total of 1,102 stomach contents were analyzed from 14 species, by the volumetric method. In general, allochthonous resources were predominant in the diets. Astyanax aff. fasciatus, Astyanax aff. paranae, Astyanax bockmanni, and Bryconamericus aff. iheringi consumed a higher proportion of plant remains, and Bryconamericus stramineus consumed predominantly Hymenoptera. The diets of Cetopsorhamdia iheringi, Characidium aff. zebra, Imparfinis schubarti, and Trichomycterus sp. consisted of aquatic insects, especially immature forms of Trichoptera, Ephemeroptera, Plecoptera, and Diptera. Hypostomus ancistroides, Hisonotus sp., Poecilia reticulata, and Rineloricaria aff. pentamaculata exploited mainly detritus, while Rhamdia quelen used a variety of items, predominantly terrestrial insects. Detrended Correspondence Analysis (DCA) showed a clear distinction among the species, with different morphology and feeding tactics. The Multi-Response Permutation Procedure (MRPP) supported this differentiation, and also indicated significant spatial and temporal variations in the dietary composition; the Indicator Value Method (IndVal) indicated the main items that contributed to these differences. The diet overlap among species was low (< 0.4) to around 78% of pairs, and the mean value did not vary significantly among the sites or between hydrological periods within each site. According to the null model of Pianka’s index, the values for dietary overlap were significantly higher than expected at random, showing evidence of resource sharing. This was related to the availability of allochthonous resources, highlighting the importance of riparian vegetation as a source of these resources for maintaining the fish fauna of the stream.