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The aim of this study was to elaborate a taxonomic survey on the testate amoebae of the Family Arcellidae in coastal streams in the State of Rio de Janeiro. Six samplings were conducted in Ubatiba coastal stream (Maricá, RJ). In total, 130 liters water were filtered through a conical net of 60-μm mesh and preserved in 4% formalin. Organisms were identified with the aid of an inverted trinocular microscope. The morphological characteristics (lobose testate amoebae with shell composed of granular chitinoid elements) of each species were recorded. The species were described and illustrated. For the verification of new taxa records of Arcellidae in Rio de Janeiro and their distribution in Brazil, a search based on index articles by Scopus, Web of Science and Google Scholar using the keywords "tecamebas", "testate amoebae", "Arcella", "Arcellidae", "Brazil" and "Rio de Janeiro", was performed. Eight Arcellidae species were recorded. Some ecological and taxonomic information was provided. Due to the small amount of information on testate amoebae, this study is important because it reduces the knowledge gap regarding this community in the State of Rio de Janeiro. Furthermore, we suggest new studies on species identification to be conducted to expand regional knowledge about these organisms. The aim of this study was to elaborate a taxonomic survey on the testate amoebae of the Family Arcellidae in coastal streams in the State of Rio de Janeiro. Six samplings were conducted in Ubatiba coastal stream (Maricá, RJ). In total, 130 liters water were filtered through a conical net of 60-μm mesh and preserved in 4% formalin. Organisms were identified with the aid of an inverted trinocular microscope. The morphological characteristics (lobose testate amoebae with shell composed of granular chitinoid elements) of each species were recorded. The species were described and illustrated. For the verification of new taxa records of Arcellidae in Rio de Janeiro and their distribution in Brazil, a search based on index articles by Scopus, Web of Science and Google Scholar using the keywords "tecamebas", "testate amoebae", "Arcella", "Arcellidae", "Brazil" and "Rio de Janeiro", was performed. Eight Arcellidae species were recorded. Some ecological and taxonomic information was provided. Due to the small amount of information on testate amoebae, this study is important because it reduces the knowledge gap regarding this community in the State of Rio de Janeiro. Furthermore, we suggest new studies on species identification to be conducted to expand regional knowledge about these organisms.

The identification of mechanisms of spatial-temporal variation, obtained from the quantification of natural populations, is a central topic of ecological research. Despite its importance to life-history theory, as well as to conservation and management of natural populations, no studies concerning movement patterns and home range of small stream-dwelling fishes from Brazilian rain forests are known. In the present study we aimed to describe the longitudinal pattern of long distance movement as well as local patterns of short movement (daily home-range) of fishes from a Mata Atlântica stream from Southeast Brazil. We gathered information about movement dynamic in order to discuss the relationship between swimming ability, fish morphology and home range. Long distance movement data were obtained in a mark-recapture experiment held in the field between June and September - 2008, on five sites along the Ubatiba stream. For this study, we had one day to mark fishes, on June-19, and 14 events for recapture. Considering the ten species that inhabit the study area, our study showed that four species: Astyanax janeiroensis, Astyanax hastatus, Parotocinclus maculicauda and Pimelodella lateristriga, moved at least 6 000m in 60 days. The other six species did not present long distance movements, as they were recaptured in the same site 90 days after being marked. For short distance study, movement data were obtained in one mark-recapture experiment held in a 100m long site subdivided into five 20m stretches where fishes were marked with different elastomer colours. We marked 583 specimens that after recapture showed two groups of different movement patterns. The first group was called “Long Movement Group” and the second one was called “Short Movement Group”. The Long Movement Group showed, on average, 89.8% of moving fishes and 10.2% of non moving fishes, against 21.3% and 78.7%, respectively, for the Short Movement Group. It was concluded that fish movement could explain the previously mentioned community stability, and that it is correlated to specific morphological attributes.A pesar de su importancia en la investigación ecológica, no se conocen estudios sobre patrones de movimiento y del ámbito de hogar de peces que habitan pequeños ríos de los bosques tropicales brasileños. El objetivo del presente estudio fue describir los patrones de movimiento de larga y corta distancia de peces de un arroyo de la Mata Atlântica (22°60” S - 42°48” W). Los datos de los movimientos de larga distancia se obtuvieron mediante un experimento de marcación-recaptura realizado en cinco sitios distribuidos a lo largo de 10km del río Ubatiba. Considerando las diez especies que habitan el área de estudio, observamos que cuatro se movieron por lo menos 6 000m en 60 días. Las otras seis especies no presentaron movimientos de larga distancia. Para los estudios de corta distancia se obtuvieron datos de marcación-recaptura en un sitio de muestreo con 100m de longitud subdividido en cinco tramos de río con 20m. Los especímenes recapturados presentaron dos grupos con patrones distintos de movimiento; un grupo con mayor movimiento y otro grupo de poco movimiento. Concluímos que el movimiento de los peces podría explicar la estabilidad de la comunidad previamente mencionada, y que está correlacionado a los atributos morfológicos específicos.

The Mato Grosso is a typical Atlantic Forest stream located on the East coast of Brazil, approximately 70km from Rio de Janeiro city. From its source at about 800m a.s.l, the stream drains a 30km² area of the Northwestern part of the municipality of Saquarema, state of Rio de Janeiro and flows into the Saquarema Lagoon system. We hypothesized that fish species occupy distinct mesohabitats, with the prediction that their occurrences and densities differ among the microhabitats of riffles, runs and pools. A 250m-long stretch of the stream located in its uppermost part was selected for this study, where it becomes second-order. Mesohabitat description and their fish characterization were undertaken. Fish sampling was conducted by electroshocking and after their identification and counting, they were returned to the stream. For mesohabitat characterization, a Discriminant Function Analysis (DA) was applied. The total number of samples was estimated by the Zippin method and the recorded densities were used as an Indicator Species Analysis (ISA), followed by a Monte Carlo test for 1 000 permutations. The DA significantly separated the three predetermined mesohabitats (pool, riffle and run) (WL=0.13, F=187.70, p=0.001). We found five species of fishes, belonging to four families and three orders. The fishes Rhamdia quelen, Phalloceros harpagos, Pimelodella lateristriga and Astyanax taeniatus are indicators of the pool environment in the Mato Grosso stream, whereas Characidium cf. vidali is an indicator of the riffle environment. The Monte Carlo test detected non-random mesohabitat use only for P. lateristriga and A. taeniatus in the pools and for Characidium cf. vidali in the riffles. We concluded that the Mato Grosso stream contains three well-defined mesohabitats, with indicator species present in two of these mesohabitats. Rev. Biol. Trop. 58 (4): 1479-1487. Epub 2010 December 01.El estudio se realizó en el Río Mato Grosso (22º55‘ S-42º35‘ W), donde se encontraron cinco especies de peces, pertenecientes a cuatro familias y tres órdenes. Teniendo en cuenta la distancia filogenética y la evidente diferencia morfológica externa entre ellos, nuestra hipótesis es que ellos ocupan distintos mesohabitats y que las ocurrencias y densidades difieren entre mesohabitats, previamente definidos como corriente, rápido y remanso. La colección de peces fue realizada por pesca eléctrica, los peces fueron identificados, contados y devueltos al arroyo. Para la caracterización de mesohabitats se aplicó un análisis de función discriminante (AD). El número total de ejemplares fue calculado por el método de Zippin y las densidades fueron utilizadas para un análisis de especies indicadoras (AIE), seguido de la prueba MonteCarlo para 1 000 permutaciones. Los tres mesohabitats fueron separados de manera significativa por AD (WL=0.13, F=187.70, p=0.00), siendo las especies Phalloceros harpagos, Pimelodella lateristriga, Rhamdia quelen y Astyanax taeniatus indicativas del ambiente de remanso, mientras que Characidium cf. Vidali del ambiente rápido. Podemos concluir que este arroyo presenta tres mesohabitats bien definidos con la presencia de especies indicadoras en estos dos mesohabitats.

The present study was conducted at the Córrego Andorinha on the eastern slope of Ilha Grande and aimed to determine the alimentary daily rhythm of Bryconamericus microcephalus. Fishes were sampled at a 4 hours interval over a 24 hours period during winter 2002 and summer 2003. Gut fullness was determined according to a numerical scale ranging from 0 (empty gut) to 3 (full gut). No differences were registered for the daily ration estimates between seasons. It is concluded that B. microcephalus is a diurnal feeding species, as the high values of gut fullness occurred between 11:00 AM and 3:00 PM.

Aspects of the reproductive biology of Astyanax janeiroensis in the Ubatiba river in Maricá, RJ, Brazil were evaluated in order to ascertain whether the strategy adopted by the species is causally related to environmental variables. Specimens were collected on a monthly basis from October 1994 to September 1995, through electrofishing. The Sex ratio was not significantly different from the expected frequency of 1:1 (G = 1.29; p > 0.50); nonetheless, considering three standard length classes, significantly larger numbers of females were recorded for the higher SL class (G = 11.07; p < 0.01). Size at first maturation showed no significant differences between sexes. Length-weight ratio analyses showed negative allometry for males and isometry, for females. Length structure was significantly different between sexes, suggesting that females are larger than males (D = 0.027, p < 0.01). Reproductive specimens were recorded during nine months of the annual cycle. Seasonal variations of reproductive specimens belonging to two different standard length classes displayed an asynchronous behavior, with larger specimens having a longer reproductive period and smaller ones reproducing for fewer months during the annual cycle. High values of fecundity (F), varying from 3169 to 18714 oocytes, were recorded for fish of 9.1 and 10.2 cm lengths, respectively. The correlation between weight and number of oocytes/unit of weight was positive, indicating that larger specimens produced more eggs.

In the present study, we describe feeding habits of Deuterodon sp. from the Ubatiba River and explore if diet changes according to a temporal cycle of dry and wet seasons. We observed that Deuterodon sp. fed on an extremely high diversity of items ranging from organic matter, sediment (sand plus quartz parts), algae, seeds and leaves to animal organisms, such as, crustaceans, oligochaets and several life stages of terrestrial and aquatic insects, indicating an omnivorous diet. An important shift in the use of feeding resources was also registered; animal and vegetal items had alternated importance between both seasons. Allochthonous vs. autochthonous items analysis showed predominance of allochthonous items during dry season while no significant differences were registered during wet season. Neste estudo descrevemos o hábito alimentar de Deuterodon sp. do rio Ubatiba e exploramos a hipótese de que as variações da dieta são função da alternância das estações seca e chuvosa. Observamos que Deuterodon sp. ingere ampla variedade de items, que variam desde matéria orgânica, sedimento (areia e partículas de quartzo), algas, sementes e folhas até organismos animais, tais como crustáceos, oligoquetas e diversos estágios de vida de insetos terrestres e aquáticos, sugerindo uma dieta onívora. Foi registrada importante alternação no uso dos recursos alimentares; itens animais e vegetais alternaram a importância durante as estações. Quanto aos recursos de origem autóctone e alóctone, registramos maior ocorrência dos últimos na estação seca e ausência de diferenças significativas para os primeiros na estação chuvosa.

Deploying mosquito predators such as the guppy ( Poecilia reticulata ) into bodies of water where mosquitoes breed is a common strategy for limiting the spread of disease-carrying mosquitoes. Here, we draw on studies from epidemiology, conservation, ecology and evolution to show that the evidence for the effectiveness of guppies in controlling mosquitoes is weak, that the chances of accidental guppy introduction into local ecosystems are large, and that guppies can easily establish populations and damage these aquatic ecosystems. We highlight several knowledge and implementation gaps, and urge that this approach is either abandoned in favour of more effective strategies or that it is used much more rigorously. Controlling mosquitoes does not need to come at the expense of freshwater biodiversity.

In this work we aimed to characterise the diet of Astyanax taeniatus (Jenyns 1842) (Characiformes, Characidae) along the Mato Grosso stream and we hypothesised that the diet of this species would vary according to spatial, seasonal and ontogenetic differences. Specimens were collected every second month at three sites with different physical attributes. The feeding habits of 651 specimens were analysed using the Alimentary Index (IAi). Analysis of the diet showed an effect of spatial, temporal and ontogenetic factors. Vegetal allochthonous items were more important in the diet of Astyanax taeniatus in upstream sites while animal autochthonous items were more important downstream. Ontogenetic differences in the diet were significant only in upstream sites, where adults consumed a greater amount of vegetal matter than juveniles. These results reinforce the idea that Astyanax species are opportunistic and show trophic plasticity. Neste trabalho, objetivou-se caracterizar a dieta de Astyanax taeniatus (Jenyns 1842) (Characiformes, Characidae) ao longo do Rio Mato Grosso, com a hipótese de que a espécie apresente variações espaciais, sazonais e ontogenéticas. Os exemplares foram coletados bimestralmente em três localidades, que diferiram pelas variáveis físicas. As preferências alimentares foram analisadas a partir de 651 exemplares, utilizando-se o Índice Alimentar (IAi). Foram avaliadas diferenças espaciais, sazonais e ontogenéticas a partir dos dados de dieta. Os itens de origem vegetal e alóctone foram mais importantes na dieta da espécie para as localidades com maior altitude, enquanto os itens animais e autóctones, na localidade baixa. Na dieta de jovens e adultos, houve diferença significativa na contribuição de itens de origem vegetal e animal somente na localidade mais alta, onde os adultos consumiram maior quantidade de matéria vegetal. Os resultados reforçam a ideia de que as espécies de Astyanax possuem hábito alimentar onívoro e oportunista, evidenciando sua alta plasticidade alimentar ao longo do riacho.

The present study was carried out in Mato Grosso fluvial system, a costal drainage from Serra do Mar. We analysed the diet and the feeding daily rhythm of Pimelodella lateristriga from samples carried out during 24 hours over a 4 hour fishing interval, in June, July and September, 2006 as well as in January and February, 2007. Diet was described from the Feeding Index (IAi) and feeding daily rhythm was verified through the Gut Fullness Index (GFI). Pimelodella lateristriga diet was composed of 37 items, being aquatic insects the most important ones. IAi analysis revealed that Diptera, Trichoptera and Ephemeroptera amounted to 90% of the diet. Autochthonous invertebrates were the most important consumed items. Pimelodella lateristriga concentrated its feeding activities in the nocturnal period (10:00 PM to 2:00 AM) with marked significant differences (F = 16.11; gl = 5; p < 0.05) between each diurnal and nocturnal periods. Between 6:00 AM and 6:00 PM, foraging activity was gradually reduced. We concluded that P. lateristriga has an insectivorous diet and a nocturnal feeding habit with greater activity between 10:00 PM to 2:00 AM. O presente estudo foi desenvolvido no sistema fluvial do rio Mato Grosso que compõe uma drenagem costeira da Serra do Mar. Foi analisado o hábito alimentar e o ritmo alimentar diário de Pimelodella lateristriga a partir de amostras obtidas em coletas de 24 horas, com intervalos de 4 horas, em junho-julho-setembro/2006 e janeiro- fevereiro/2007. A dieta foi avaliada a partir do Índice Alimentar (IAi) e o ritmo alimentar diário, com base no Índice de Repleção Estomacal (GFI) dos peixes. A dieta de P. lateristriga foi composta por 37 itens, sendo os insetos aquáticos os mais abundantes. O IAi revelou que Diptera, Trichoptera e Ephemeroptera somaram 90% da dieta, sendo, portanto, os invertebrados autóctones os itens mais consumidos. Pimelodella lateristriga concentrou sua atividade alimentar no período noturno (10:00 até 14:00 horas) com diferenças significativas (F = 16,11; gl = 5; p < 0,05) entre os horários diurnos e noturnos. Entre os horários 6 am e 6 pm a atividade de forrageamento foi gradualmente reduzida. Concluímos que P. lateristriga possui dieta insetívora e ritmo alimentar noturno com pico de atividade entre 10:00 até 14:00 horas.

The reproductive strategy of two congeneric species (Astyanax janeiroensis - AJ and Astyanax hastatus - AH) was assessed, in order to address the costs imposed by different investment patterns, on four major life history characters: migratory behaviour, breeding time, fecundity and egg size. Altitudinal segregation of young and adult individuals plus data from the literature indicated that AJ is a migratory species, whereas AH is non migratory. Breeding season (BS) analysis revealed that AH was reproductively active year-round (12 months), whereas AJ breeds during 9 months. Brood costs (Ovarian Investment) were almost the same for both species (AJ - 364 oocytes / g and egg volume = 0.52 mm³; AH -702 oocytes / g and egg volume = 0.27 mm³). Reproductive costs (RC), considered as product of gamete production (OI) and gamete output (BS), were 1,703.7 for AJ and 2,274.0 for AH; thus RC is 25% higher in AH. It is concluded that the costs with OI (egg size and egg numbers) are equal for both species but as breeding season is larger for AH the overall strategy is 25% more expensive in AH. Thus, it is hypothesized that this 25% should be considered as the extra costs that AJ uses during migration and is compensated by its shorter breeding time (9 months versus 12 months of AH). A estratégia reprodutiva de duas espécies congenéricas (Astyanax janeiroensis - AJ e Astyanax hastatus - AH) foi analisada a fim de se determinar os custos energéticos impostos por diferentes padrões de investimento em quatro dos principais caracteres da história de vida de peixes: comportamento migratório, estação reprodutiva, fecundidade e tamanho dos ovócitos. A segregação espacial dos indivíduos jovens e adultos associada a informações da literatura indicaram que AJ é uma espécie migratória enquanto AH não migra. A análise sobre a estação reprodutiva (ER) revelou que AH se reproduz ao longo de todo o ciclo anual (12 meses) enquanto AJ se reproduz durante 9 meses. Os custos com a desova (Investimento Ovariano - IO) foram similares nas duas espécies (AJ - 364 ovócitos/g e volume dos ovócitos = 0,52 mm³; AH - 702 ovócitos/g e volume dos ovócitos = 0,27 mm³). O custo da reprodução (CR), considerado como o produto da produção de gametas (IO) e o tempo de liberação dos gametas (ER), foram 1.703,7 para AJ e 2.274,0 para AH; assim CR é 25% superior em AH. Concluímos assim, que os custos com IO (tamanho e número de ovócitos) são iguais para as duas espécies, mas como a estação reprodutiva é maior para AH, a estratégia como um todo é mais custosa para AH. Dessa forma, sugerimos que os 25% excedentes podem ser considerados como os custos extras que AJ necessita para a migração e são compensados pelo menor tempo da estação reprodutiva (9 meses em AJ versus 12 meses em AH).

Four samplings were carried out during the dry and rainy seasons in 2014, in two biotopes (plankton and aquatic macrophytes) to assess the composition and species richness of testate amoebae community in a coastal stream in the state of Rio de Janeiro, Brazil. Results showed great representation of Difflugiidae, Centropyxidae, Lesquereusiidae and Arcellidae families. Higher richness was observed in the plankton samples and higher densities of testate amoebae were reported among the aquatic vegetation during the dry season. Current investigation is a pioneer study conducted in the Ubatiba stream. Further researches on these protists, especially in Rio de Janeiro, should be undertaken.

High mortality rates have been observed in Teleost during early developmental stages, as well as great variations in reproductive tactics, which are related to adaptations towards environmental conditions and ecological niches for which different species have a specific response. The objective of this study was to describe reproductive tactics related to the survival of Cichlasoma orientale offspring, including aspects of body size, parental care, fecundity, oocyte size and spawning patterns. Samples were performed monthly from August 2011 to July 2013, in lentic and lotic environments at Curu river basin, Brazilian Northeastern semiarid region. Individual behavior (n=113) was observed underwater for over 50 hours by ad libitum sampling and focal-animal sampling. Collected individuals (males n=185, females n=95) were evaluated regarding the standard length, batch fecundity, oocyte size and spawning pattern. In females with mature ovaries, oocyte groups at different developmental stages were observed, these cells were counted and measured, and fecundity was estimated by the gravimetric method. Our results showed that the species displayed biparental care behavior and, on average, males were larger than females. Based on 46 ovaries, the average batch fecundity was 2 052±849 (range: 254-3 389). Standard length and batch fecundity were positively correlated, but no correlation was found between oocyte size and standard length. The maximum diameter observed in the most developed oocytes was 1.8mm. The observed distribution of oocyte size classes indicated synchronous oocyte development in three groups: previtellogenic, vitellogenic and mature, showing that C. orientale is a multiple spawner. Differences in the amount of oocytes among the three groups were observed, with the most developed group showing the smallest number of oocytes. The combination of low fecundity and large egg size is characteristic of demersal spawners due to a greater environmental stability. Multiple spawning increases chances of survival mainly because of increased fecundity per reproductive season, and the reduced competition among the offspring. We concluded that C. orientale makes a heavy investment in larval survival in detriment of the offspring number. Survival is favored by the large size of oocytes, large yolk reserve, biparental care and multiple spawning pattern.

The Ubatiba river is a coastal stream subject to stochastic spates all over the year and, Characidium sp.n. is among the twenty-two species that compose its ichthyofauna. In this study we analyse some traits of its reproductive biology and discuss whether the adopted strategy has causal relationship with the environmental variables. Specimens were collected in the upper Ubatiba river. Samplings, were carried out monthly by electrofishing, between Oct./94 and Sep./95. Some differences between male and female strategies were observed. Females were significantly (p < 0.05) bigger than males; length -- weight relationship was different (p < 0.05) between sexes with the onset of sexual maturity occuring at smaller sizes among males. Reproductive investment is high for both males and females but higher for males, maximum Gonadosomatic Index for females and males were 40.97% and 44.90%, respectively. Reproductive specimens were registered all over the year, suggesting continuous reproduction. High values of fecundity were also registered varying from 1342 to 5535 eggs for ripe females of 4.4 and 7.0 cm, respectively and an amount of 1105 oocytes per grams of fish. We suggest that differences in the reproductive strategy, between sexes, determine the observed patterns in the size structure; the absence of males in the higher SL classes could be a consequence of high mortality rates and/or reduction in the growth rates as a precocity consequence in the onset of reproduction and/or high reproductive investment. Relationship between continuous reproduction and environmental condition could be explained as an adaptation to maximise supervivency of the young fishes that is: guarantee the species maintenance in a stochastic environment. O rio Ubatiba é um riacho costeiro sujeito a chuvas torrenciais imprevisíveis e Characidium sp.n. é uma das 22 espécies que compõem sua ictiofauna. Neste estudo, são analisados alguns aspectos de sua reprodução e discutidas possíveis relações de causalidade entre a estratégia adotada e a situação ambiental. Os exemplares estudados são provenientes do trecho superior do rio Ubatiba. As coletas foram realizadas mensalmente, por pesca elétrica, entre out./94 e set./95. Foram registradas algumas diferenças nas estratégias de machos e fêmeas. As fêmeas foram significativamente (p < 0,05) maiores que os machos; a relação peso/comprimento é significativamente diferente (p < 0,05) entre os sexos; e na primeira maturação também há diferenças entre os sexos. O investimento reprodutivo é alto para ambos os sexos, mas levemente superior para os machos, sendo o Índice Gônado Somático máximo de fêmeas e machos de 40,97% e 44,90%, respectivamente. Exemplares reprodutivos foram freqüentes ao longo de todo o ano, sugerindo que a reprodução da população é contínua. A fecundidade variou de 1.342 a 5.535 ovócitos para fêmeas maduras de 4,4 a 7,0 cm, respectivamente, sendo produzidos 1.105 ovócitos por grama de peixe. Sugerimos que as diferenças na estratégia reprodutiva de machos e fêmeas determinam o padrão observado na estrutura de tamanho, sendo a ausência de machos nas maiores classes de SL conseqüência da precocidade da 1ª maturação e/ou do alto investimento reprodutivo. A relação entre a reprodução contínua da população e as condições ambientais poderiam ser explicadas como uma adaptação para maximizar a sobrevivência de jovens, isto é, garantir a manutenção da espécie em um ambiente imprevisível.

In the present study we aimed to compare the feeding ecology of Hypostomus punctatus from a coastal stream from Southeast Brazil with data previously published for the same study site before environmental changes. Feeding preferences were assessed through a sample of 138 specimens (67 from the dry and 71 from the rainy season) using the Index of Alimentary Importance (IAi). We registered five different food items (detritus, plant fragments, Diatoms, Chloroficeae and Cianobacteries) composing the species diet. Detritus was the most abundant one both during the rainy and dry seasons (IAirainny = 90.34 and IAidry = 96.30). No significant differences were registered for the volume of food items consumed during the rainy and dry seasons. The Frequency of Occurrence analysis showed that four (detritus, plant fragments, Diatoms and Chloroficeae) among the five all other consumed ones, were always frequent. Comparing our own results with those available for the study site, we suggest that the feeding habit of H. punctatus has changed according to environmental changes and that the species diet is strongly dependent upon environmental conditions.

Spatio-temporal changes in the diet, niche breadth and niche overlap of two species of Characidium from three different sites along a Neotropical coastal stream were studied during a dry and rainy season. Seasonal changes were restricted to the occurrence of plant items in the stomach contents. The relative importance of food items in the diet of both species varied across sites, but Diptera, Ephemeroptera, Simuliidae, Trichoptera and Coleoptera larvae were always the main prey items. Contrary to the expected pattern, values of the niche breadth were higher at the site where Characidium species co-existed and niche overlapped at this site indicated 52% (p = 0.52) of feeding overlap.

Key to understand predator choice is the relationship between predator and prey abundance. There are few studies related to prey selection and availability. Such an approach is still current, because the ability to predict aspects of the diet in response to changes in prey availability is one of the major problems of trophic ecology. The general objective of this study was to evaluate prey selection by two species (Characidium cf. vidali and Pimelodella lateristriga) of the Mato Grosso stream, in Saquarema, Rio de Janeiro, Brazil. Benthos and fishes were collected in June, July and September of 2006 and January and February of 2007. Fish were collected with electric fishing techniques and benthos with a surber net. Densities of benthic organisms were expressed as the number of individuals per/m2. After sampling, the invertebrates were fixed in 90% ethanol, and, in the laboratory, were identified to the lowest taxonomical level. Approximately, seventy individuals from each species were selected randomly in each month. Fishes were fixed in 10% formalin in the field and transferred to 70o GL ethanol in the laboratory. Fishes had their stomachs removed for subsequent analysis. Fish diet was described according to the numeric frequency method. The Manly Electivity I ndex was applied in order to verify prey selection. The most abundant families in both benthos and diet of both fish species were the same, indicating that these species consume mainly most abundant prey in the environment. We concluded that prey selection occurs even for preys that had small abundance in the environment . However, it is the availability of the macroinvertebrate resources that determines the major composition of items in diet of fish, demonstrating that the abundance is the factor that most influences the choice of prey. Rev. Biol. Trop. 59 (4): 1697-1706. Epub 2011 December 01.Existen muy pocos estudios relacionados con la selección y disponibilidad de las presas por parte de sus depredadores. Actualmente, este enfoque se mantiene, debido a que uno de los principales problemas de la ecología trófica es la capacidad de predecir los aspectos de los hábitos alimentarios en respuesta a los cambios en la disponibilidad de las presas. El objetivo general de este estudio fue evaluar la seleccion de las presas en los especies (Characidium cf. vidali y Pimelodella lateristriga) del arroyo Mato Grosso en Saquarema, Rio de Janeiro. Se recolectaron bentos y peces en junio, Julio y septiembre 2006 y en enero y febrero 2007. Los peces fueron recolectados con técnicas de pesca eléctrica y los del bentos con una red surber. La densidad de los organismos bentónicos se expresó como el número de individuos por m2. Luego del muestreo, los invertebrados se fijaron en 90% de etanol y se identificaron con el nivel taxonómico más bajo. Los peces fueron fijados con 10% de formalina en el campo y transferidos a etanol 70o GL en el laboratorio. Los estómagos de los peces fueron extirpados para su posterior análisis. Las familias más abundantes del bentos y las dietas de los peces fueron las mismas, lo que indica que estas especies consumen principalmente la presa más abundante en el ambiente. Se concluye que la selección de la presa se produce incluso para aquellas presas con una abundancia pequeña en el entorno. Sin embargo, es la disponibilidad de los recursos de los macroinvertebrados la que determina la mayor composición en términos de la dieta de los peces, demostrando que la abundancia es el factor que se ve más influenciado por la elección de presas