Abstract Notholebias minimus is an endangered annual killifish endemic to the coastal plains of the State of Rio de Janeiro, Brazil. This study aimed to present new occurrences in the Atlantic Forest biome, provide unprecedented population features (body and egg size, fecundity, sexual ratio, and length-weight relationship – LWR), and compare changes in land use and coverage between 1985 and 2021 in biotopes located inside and outside protected areas. Three new occurrence localities were found in shallow temporary wetlands with acidic pH (6.4 ± 0.2) and low concentrations of dissolved oxygen (2.0 ± 0.9 mg/L). Males and females total length ranged from 11.1 to 31 mm and 11 to 26 mm, respectively. Batch fecundity ranged from 18 to 40 oocytes (24.8 ± 8.8), corresponding to oocytes with sizes between 800–1,006 µm (905 ± 56). Males were significantly larger than females (W = 2193.5, p = 0.0067), but both sexes occurred in similar proportions (p = 0.472). LWR showed positive allometry (b = 3.18). Biotopes located within protected areas exhibited higher conservation. Our discoveries expand the knowledge about habitat and population features of N. minimus and reinforce the importance of establishing protected areas for the conservation of annual fish biotopes.

Resumo Notholebias minimus é um peixe anual ameaçado de extinção, endêmico das planícies costeiras do Estado do Rio de Janeiro, Brasil. Neste estudo, objetivamos apresentar novas ocorrências no bioma Mata Atlântica, fornecer características populacionais inéditas (tamanho do corpo e dos ovos, fecundidade, proporção sexual e relação peso-comprimento), e comparar mudanças no uso e cobertura do solo entre 1985 e 2021 em biótopos localizados dentro e fora de unidades de conservação. Registramos três novos locais em áreas úmidas temporárias rasas com pH ácido (6,4 ± 0,2) e baixas concentrações de oxigênio dissolvido (2,0 ± 0,9 mg/L). O comprimento total de machos e fêmeas variou de 11,1 a 31 mm e de 11 a 26 mm, respectivamente. A fecundidade do lote variou entre 18–40 oócitos (24,8 ± 8,8), correspondendo a diâmetros entre 800–1.006 µm (905 ± 56). Os machos foram significativamente maiores que as fêmeas (W = 2193,5; p = 0,0067), mas ocorreram em proporções similares (p = 0,472). A relação peso-comprimento detectou alometria positiva (b = 3,18). Biótopos localizados dentro de áreas protegidas exibiram maior preservação ambiental. Nossas descobertas ampliam o conhecimento sobre as características do habitat e da população de N. minimus e reforçam a importância do estabelecimento de áreas protegidas para a conservação dos biótopos dos peixes anuais.

Resumo A complexidade de avaliar a qualidade de um ambiente aquático com suas inúmeras variáveis resultou na criação de vários índices de qualidade para sintetizar todas as informações em um único valor. No entanto, a maioria desses índices é baseada em poucas variáveis, perdendo informações de outras variáveis relevantes. Este artigo apresenta um novo modelo capaz de representar o nível de qualidade de um reservatório oligo-mesotrófico tropical em escala numérica, considerando a subjetividade implícita no conceito de qualidade e envolvendo diversas variáveis físicas, químicas e biológicas. O modelo proposto, denominado "Índices Fuzzy de Avaliação da Qualidade da Água e Biótica" (FUZZY-WBQAI), é baseado em sistemas de inferência fuzzy, fornecendo uma forma de lidar com a incerteza entre as categorias de qualidade. Uma ferramenta computacional foi elaborada, a qual avalia automaticamente a qualidade da água, considerando diferentes metodologias que dependem das condições de estratificação e zona longitudinal do reservatório. O modelo calcula dois índices: um de qualidade da água e um biótico que utiliza métricas da assembleia de peixes. O modelo foi eficaz ao revelar a diminuição da qualidade da água nos meses de verão com temperatura e precipitação mais elevadas. Destacou-se o efeito da mistura do reservatório estratificado no inverno sobre a diminuição da qualidade da água em área de cultivo de peixes. O índice biótico foi sensível a mudanças espaciais na qualidade ambiental do reservatório. Os resultados foram considerados satisfatórios, concordando com o conhecimento especializado, e podem propiciar diagnósticos rápidos das condições da água em reservatórios oligo-mesotróficos nos trópicos.

Abstract The complexity of evaluating the quality of an aquatic environment with its numerous variables has resulted in several quality indexes to synthesize all information in a single value. However, most of these indexes are based on few environmental variables, losing information from other relevant variables. This article presents a new model capable of representing the quality level of a tropical oligo-mesotrophic reservoir on a numerical scale, considering the subjectivity implicit in the concept of quality, and involving several physical, chemical and biological variables. The proposed model, called "Fuzzy Indices for Water Quality Assessment and Biotics" (FUZZY-WBQAI), is based on fuzzy inference systems, providing a way to deal with the uncertainty between the quality categories. A computational tool was developed, which automatically assesses the quality of water, considering different methodologies that depend on the stratification conditions and the longitudinal zone of the reservoir. The model calculates two indices: one for water quality and one biotic that uses metrics from the fish assembly. The model was effective in revealing the decrease in water quality in summer months with higher temperature and precipitation. The effect of the mixture of the stratified reservoir in winter in decreasing the water quality in an area of fish cultivation was highlighted. The biotic index was sensitive to spatial changes in the environmental quality of the reservoir. The results were considered satisfactory, in agreement with the specialized knowledge, and can provide a rapid diagnosis of water conditions in oligo-mesotrophic reservoirs in the tropics.

Resumo: Foram examinadas as mudanças sazonais na dieta e relacionadas ao tamanho para o tucunaré Cichla kelberi em um reservatório tropical de várzeas no Sudeste do Brasil em três ciclos hidrológicos: verão (elevadas precipitações e temperaturas), inverno (baixas precipitações e temperaturas), e final da primavera (aumentos das precipitações e temperaturas) durante dois anos (2006-2007). A hipótese testada é que este peixe predador não-nativo muda a dieta durante as fases adulta e subadulta e entre as estações do ano para se adaptar neste novo ambiente colonizado. Peixes das famílias Clupeidae (Platanichthys platana), (Characidae (Astyanax spp.) e Cichlidae (Cichla kelberi) foram os itens alimentares mais importantes, seguidos por insetos da ordem Odonata. O canibalismo também foi registrado para os maiores indivíduos. Mudanças significativas na dieta foram relacionadas ao tamanho, com os indivíduos menores (Comprimento Total, CT <20 cm) utilizando principalmente peixes, enquanto os indivíduos maiores (CT >20 cm) se alimentaram principalmente de Odonata. A amplitude de nicho aumentou ao longo do crescimento, com indivíduos de maior porte tendo dieta mais uniformemente distribuída entre os recursos disponíveis. Nenhuma diferença significativa na composição da dieta foi encontrada entre as estações do ano, mas estômagos com maiores volumes ocupados pelo alimento foram mais frequentes no fim da primavera e menos frequentes no verão. Por outro lado, a maior amplitude de nicho foi encontrada no verão comparada com as outras estações, o que indica o uso mais uniforme dos diversos recursos disponíveis. Juntas, estas observações sugerem uma utilização eficiente dos recursos disponíveis por esta espécie predadora de topo neste novo sistema colonizado.

Abstract: We examined size-related and seasonal changes in the diet of the peacock bass Cichla kelberi in a tropical lowland reservoir in southeastern Brazil over three hydro-climatic seasons: summer (high rainfall and temperature), winter (low rainfall and temperature), and late spring (increasing rainfall and temperature) during two years (2006-2007). The tested hypothesis is that this non-native predator fish changes diet during the subadult and adult phases and among seasons to adapt in new colonized environment. Fishes of the families Clupeidae (Platanichthys platana), Characidae (Astyanax spp.) and Cichlidae (Cichla kelberi) were the most important food items, followed by insects of the order Odonata. Cannibalism was also recorded for the largest individuals. A significant size-related change in diet was found with the smallest individuals (Total Length, TL < 20 cm) preying mainly on fishes, whereas the larger individuals (TL > 30 cm) preyed mainly on Odonata. The niche breadth increased during growth, with the largest individuals having a diet more evenly distributed among the available resources. No significant seasonal differences in diet composition were found, but stomachs with higher degree of volume occupied by food were more frequent in late spring than in summer. Conversely, the highest niche breadth was found during the summer compared to the other seasons. Together, these observations suggest an efficient use of the available resources by this top predator in this new colonized system.

ABSTRACT Phoretic relationships often bring large advantages to epibionts. By attaching themselves to mobile hosts, epibionts are able to: expand their ranges without spending energy, reduce their risk of being predated, and increase their probability of finding food. We assessed the phoretic relationship between the siluriform fish Ancistrus multispinis (Regan, 1912) and the chironomid larva Ichthyocladius sp. in three streams of the Atlantic forest in southeastern Brazil. We evaluated changes in epibiont distribution throughout the body regions of the host and among three different aquatic systems. We had predicted that certain body regions are more prone to support epibiont attachment, and that epibiont prevalence increases with increased host size and quality of the aquatic system. Three streams (Santana, São Pedro and D’Ouro), tributaries of the Guandu River, were sampled during 2010 and 2011. A total of 102 specimens of A. multispinis were collected and analyzed. Epibionts were found in fourteen of fifteen body regions of the host. Observation from scanning electron microscopy revealed that Chironomidae larvae fix themselves to the spicules through the anal prolegs, not at the skin, as previously reported. The amount of epibionts (degree of infestation) was significantly correlated with fish size in the Santana Stream (r = 0.6, p < 0.01), and São Pedro Stream (r = 0.56, p < 0.01), but not in the D’Ouro Stream, the most altered of the three. The pre sence of epibionts on the body of the fish is directly correlated with the availability of spicules on the fish’s body, the largest numbers of infestations being found in structures associated with swimming (caudal and pectoral fins), since the swimming movement can create favorable conditions (e.g., suspension of organic particles, increasing oxygenation) for the epibiont.

RESUMO A sub-rotina simulação de habitat físico da metodologia incremental - IFIM usa variáveis hidráulicas e os índices de aptidão das espécies alvo para predizer como diferentes vazões afetam a ocupação de microhabitat por espécies de peixes. Esta abordagem de simulação de hábitat foi adotada para avaliar os efeitos ecológicos sobre três espécies de peixes tropicais de diferentes ordens (Bryconamericus ornaticeps , Ancistrus multispinis e Geophagus brasiliensis ) em dois trechos de um riacho de Mata Atlântica do sudeste do Brasil, durante a estação chuvosa de 2013 e a estação seca de 2014. Características topográficas e hidráulicas (profundidade, velocidade e tipo de substrato) foram mensuradas para implementação da simulação de habitat em uma dimensão; observações subaquáticas dos peixes foram realizadas para avaliação do uso do microhabitat. As curvas de aptidão de habitat de cada variável hidráulica foram utilizadas na simulação de habitat para obtenção das curvas de aptidão composta (HSI) e a área útil ponderada (WUA) versus fluxo, e propor vazões ambientais mínimas e ideais para as espécies de peixes-alvo. A amplitude de vazão de 0,65-0,85 m3/s foi registrada como o ótimo para satisfazer as necessidades das três espécies de peixes. Esta é uma informação objetiva para os gestores de recursos hídricos e que pode ser aplicada no planejamento de programas de gestão visando a conservação dos ecossistemas. Desse modo, pode ser considerado um estudo piloto bem sucedido na avaliação do fluxo ambiental em um riacho da Mata Atlântica do Brasil.

ABSTRACT The physical habitat simulation sub-routine of the Instream Flow Incremental Methodology (IFIM) uses hydraulic modeling and suitability indices of target fish species to predict how differences in-stream flows affect the microhabitat occupation by fish species. This habitat modelling approach was adopted to assess the ecological effects of running flows on three neotropical fish species of different orders (Bryconamericus ornaticeps , Ancistrus multispinis and Geophagus brasiliensis ).The study encompassed two reaches of an Atlantic Forest stream in Southeastern Brazil where topographic and hydraulic (depth, velocity and type of substrate) characteristics were measured to implement one-dimensional hydraulic simulation. Sub aquatic observation of fish was performed to collect data on microhabitat use and these data were used to develop habitat suitability curves that were used in the habitat simulation to obtain the habitat suitability index (HSI) and weighted usable area (WUA) versus flow curves. Upon these curves minimum and optimum environmental flows for the target fish species were proposed. Bryconamericus ornaticeps and A. multispinis selected microhabitats around 0.6 m depth, whereas G. brasiliensis showed a wider suitable range (0.35-0.9 m). All the three species were mainly observed in microhabitat with low flow velocity (0.1 m/s). Bryconamericus ornaticeps selected more frequently coarse substrate (e.g. boulders) but it appeared also over sandy substrate, whereas A. multispinis and G. brasiliensis selected preferably boulders. The range of 0.65-0.85 m3/s was found as the optimum to meet the needs of the three fish species. Our results agree with the necessary objective information to perform grounded management actions in the frame of a management program aiming at ecosystem conservation. Thereby it can be considered a successful pilot study in environmental flow assessment in an Atlantic Forest stream of Brazil.

Enzymatic activities for digestion of proteins and carbohydrates were compared among three organs of the digestive system of Pimelodus maculatus in two reservoirs with different trophic conditions during the winter of 2006. The aim was to test the hypothesis that enzymatic activity for the digestion of proteins and carbohydrates differed among organs and that such activities differ between the trophic state of the environment. Enzymatic activities were determined through the assays of specificity for trypsin, chymotrypsin and β-glucosidase enzymes. The intestine had higher trypsin-like enzymatic activities compared to the stomach and liver. The highest β-glucosidase activity was found in the liver compared to the stomach and intestine in the oligotrophic reservoir only. Overall, enzymatic activity did not differ between the eutrophic and oligotrophic reservoirs, although the intestinal chymotrypsin was comparatively higher in the eutrophic reservoir and the hepatic β-glucosidase was higher in the oligotrophic reservoir. These findings indicated that most digestive activity occurred in the intestine for P. maculatus, which was probably related to its omnivorous/carnivorous feeding habits. The highest proteolytic activity in the intestine was expected for most fishes, but the high hepatic β-glucosidase in the oligotrophic reservoir was unexpected. The hepatic β-glucosidase as well as the intestinal chymotrypsin-like activity could be considered as the candidates for biomarkers of environmental quality.

Onze atributos ecomorfológicos e a dieta de dezessete espécies de peixes juvenis foram examinados para testar a hipótese de que os padrões morfológicos determinam a utilização dos recursos em habitats estuarinos. As espécies foram separadas de acordo com o modo de captura do alimento e uso do habitat (bentônicos ou pelágicos) em três grupos distintos: (1) um grupo de peixes depressiformes, com forte pedúnculo caudal e nadadeiras peitorais alargadas; (2) um segundo grupo, compressiforme, com ampla boca protrusível, e (3) um terceiro grupo, fortemente achatado e com pequenas nadadeiras peitorais. Seis grupos tróficos foram organizados com base nas categorias de presas: Zooplanctívoros, Bentívoros, Omnívoros, Detritívoros, Macrocarnívoros e Insetívoros. Foram encontrados resultados significativos (PERMANOVA) entre os índices ecomorfológicos e o habitat e entre os índices ecomorfológicos e os grupos tróficos. Estes dados indicam que a similaridade ecomorfológica, que reflete o ambiente e o tipo de alimento consumido, facilitaria a coexistência desses peixes quando estes são abundantes neste estuário tropical.

Eleven ecomorphological attributes and diet of seventeen juvenile fish species were examined to test the hypothesis that morphological patterns determine resource uses in estuarine habitats. Species were separated according to the apparatus to food capture and habitat use (benthic or pelagic) in three different groups: (1) a group with depressed fish body, strong caudal peduncle and enlarged pectoral fins; (2) a second group laterally flattened with a wide protruding mouth, and (3) a third group strongly flattened with small pectorals fins. The following six trophic groups were organized based on prey categories: Zooplanktivores, Benthivores, Omnivores, Detritivores, Macrocarnivores and Insectivores. Significant results (PERMANOVA) between ecomorphological indices and habitat and between ecomorphological indices and trophic groups were found. These data indicate that similarity of ecomorphological forms, which minimize the influence of environment and partitioning of food, would help facilitate the co-existence of these fish when they are abundant in this tropical estuary.

The Gram-negative intestinal microbiota of Hypostomus auroguttatus and Pimelodus maculatus, a detritivorous and an omnivorous fish species, respectively, were compared between fishes from the reservoir and the stretch of the river below the dam of the Funil hydroelectric plant, Rio de Janeiro, Brazil. Four selective culture media were used under aerobic and two under anaerobic conditions. The omnivorous species had microbiota with higher population levels compared to the detritivorous species. The number of morphotypes and population levels of total bacteria, vibrio and Bacteroides tended to be higher in summer and autumn in the reservoir, and not different in the river. The number of morphotypes of enterobacteria and total bacteria were higher in the lotic environment compared with the lentic one. The bacteria Aeromonas hydrophila and Plesiomonas shigelloides and the obligate anaerobic Fusobacterium mortiferum were the most frequently identified microorganisms in the intestine of both H. auroguttatus and P. maculatus. Both season and habitat influenced the Gram-negative intestinal microbiota of H. auroguttatus and P. maculatus. Environmental factors influenced the Gram-negative intestinal microbiota of both species with possible impact on the interrelationship between the fishes and their digestive ecosystem, although the gut microbiota composition of fishes may result from host-specific selective pressures within the gut.

The enzymatic activities involved in the digestion of proteins and carbohydrates were compared among three organs of the digestive track of two Siluriformes fish species, and between two areas: a reservoir, and an area downriver of it. Our aim was to test the hypothesis that the digestive organs of species with varied feeding habits have different enzymatic activities, and that the enzymatic activity differs among seasons and environmental conditions. The iliophagous/herbivorous species Hypostomus auroguttatus Kner, 1854 had higher trypsin-like, chymotrypsin-like peptidase and β-glucosidase activity in the intestine when compared with the omnivorous species Pimelodus maculatus Lacepède, 1803, whereas the latter had more hepatic trypsin-like activity than the former. The peak of activity of the three enzymes in H. auroguttatus was recorded in the winter and spring. On the other hand, P. maculatus tended to have the more prominent peptidase and β-glucosidase activity in the summer, and the smallest in the winter. The intestine of H. auroguttatus had higher enzymatic (trypsin, chymotrypsin and β-glucosidase) activity than the stomach and the liver. For P. maculatus, the highest β-glucosidase activity was found in the liver. The enzymatic activity of H. aurogutattus did not differ between lotic and lentic systems, whereas P. maculatus had comparatively higher stomach and hepatic trypsin levels and hepatic chymotrypsin-like activities in the reservoir than down in the river. These findings indicate that, in H. auroguttatus, most digestive activity occurs in the intestine, which is long and adapted for the digestion of bottom-river vegetable matter and detritus. The seasons and the type of the system (lentic vs. lotic) seem to affect the enzymatic activity for these two species differently, a likely consequence of their different lifestyles.

Determinamos neste estudo a preferência de habitat de sete espécies de peixes abundantes em um rio regulado do Sudeste do Brasil. Testamos a hipótese de que peixes diferem na preferência de habitat e usam trechos do rio com diferentes características hidráulicas e tipos de substratos. Realizamos amostragens de peixes, utilizando redes de espera e tarrafas em quatro trechos do rio de 1 km de extensão, compreendendo diferentes características do habitat, onde também obtivemos medidas de profundidade, velocidade da água e tipo de substrato. Quatro Siluriformes (Loricariichthys castaneus, Hoplosternum littorale, Pimelodus maculatus e Trachelyopterus striatulus) e três Characiformes (Astyanax aff. bimaculatus, Oligosarcus hepsetus e Hoplias malabaricus) que juntos compreenderam aproximadamente 70% do número total e 64% do peso total de peixes foram estudados. Classificamos os peixes em quatro guildas: (1) peixes que ocorrem em trechos com baixa velocidade de fluxo e substrato constituído predominantemente de lama e areia, compreendendo dois Siluriformes, um de áreas rasas (< 4 m, i.e., H. littorale) e outro de áreas profundas (> 8 m, i.e., L. castaneus); (2) peixes que utilizam rápidos de áreas laterais mais profundas com substrato lamoso, representados pelos pequenos Characiformes, A. aff. bimaculatus e O. hepsetus; (3) peixes que utilizam rápidos que ocorrem em áreas rasas e substrato arenoso, representado por T. striatulus; e (4) peixes de corredeiras que utilizam as margens rasas com fundo lamoso, representados por H. malabaricus e P. maculatus. As espécies estudadas apresentam diferenciação na preferência por variáveis do hábitat, corroborando a hipótese investigada.

We determined in this study the habitat preferences of seven native fish species in a regulated river in Southeastern Brazil. We tested the hypothesis that fishes differ in habitat preference and that they use stretches of the river differing in hydraulic characteristics and substrate type. We surveyed fishes in four 1-km long river stretches encompassing different habitat traits, where we also measured water depth, velocity, and substrate type. We investigated preference patterns of four Siluriformes (Loricariichthys castaneus, Hoplosternum littorale, Pimelodus maculatus, and Trachelyopterus striatulus) and three Characiformes (Astyanax aff. bimaculatus, Oligosarcus hepsetus, and Hoplias malabaricus), representing approximately 70% of the total number of fishes and 64% of the total biomass. We classified fishes into four habitat guilds: (1) a slow-flowing water guild that occupied mud-sand substrate, composed of two Siluriformes in either shallow (< 4 m, i.e., H. littorale) or deep (> 8 m, L. castaneus) waters; (2) a run-dwelling guild that occurs in deep backwaters with clay-mud substrate, composed of the Characiformes A. aff. bimaculatus and O. hepsetus; (3) a run-dwelling guild that occurs in sandy and shallow substrate, composed of T. striatulus; and (4) a fast-flowing guild that occurs primarily along shorelines with shallow mud bottoms, composed of H. malabaricus and P. maculatus. Our hypothesis was confirmed, as different habitat preferences by fishes appear to occur in this regulated river.

In this work we describe the gonad morphology and spawning season of Hypostomus affinis (Steindachner, 1877) in a tropical reservoir based on 55 males and 125 females. Our aim was to assess eventual adaptations in reproductive tactics developed by this riverine species inhabiting an oligotrophic reservoir with low habitat complexity, few rocks and few other preferred consolidated substrata. We described the stages of cells of reproductive lineage, gonadal development and some reproductive traits which were compared with information in the available literature. Cells from the spermatogenic lineage were spermatogonia, spermatocytes, spermatids and spermatozoa, and cells from the oocytarian lineage were primary oocytes, previtelogenic oocytes, cortical vesicle oocytes and yolk globules or vitellogenic. Five stages were described for the males/females according to the distribution of oocytes and spermatogenic lineage cells: resting; initial maturation; advanced maturation; partially spent/spawned; totally spent/spawn. Females outnumbered males and reached larger size. Synchronic ovary development in two groups was found with diameter of mature oocytes ranging from 2 to 3.35 mm. Indication of early maturation, a longer reproductive period and the production of smaller eggs in small clutches seems to be features of the reservoir population not found in riverine systems. Such changes in tactics may indicate a shift to an opportunistic strategy, helping the population to withstand environmental constraints and to succeed in this oligotrophic and poorly structured reservoir.

ABSTRACT With the construction of the ‘Lajes’ reservoir, ‘Rio Light’ power company, nowadays ‘LIGHT S.A.’, began the construction of a hydroelectric power plant complex to supply the increasing demand for electric energy of the metropolitan area of Rio de Janeiro. Although causing heavy environmental damages, the first part of the ‘Lajes’ complex was a turning point and a great advancement at the time (the beginning of the twentieth century) when a 30 km2 surface water reservoir was built for hydroelectric power generation. This study aims to record a little of this history by presenting government policy conflicts, law disputes and the destruction of the whole municipality of Sao Joao Marcos-RJ.

RESUMO Com a construção do reservatório de Lajes, a Rio Light, hoje LIGHT S.A., deu início à construção de um Complexo Hidrelétrico para atender à crescente demanda da região metropolitana do Rio de Janeiro por energia elétrica. Embora extremamente impactante, essa primeira obra do Complexo de Lajes foi um marco e um grande avanço para a época (início do séc. XX), pois, afinal de contas, construiu-se um reservatório com um espelho d’água de 30 km2 para a geração de energia elétrica por força hidráulica. Este trabalho busca apresentar de forma concisa um pouco dessa história marcada por conflitos de interesses políticos, longas disputas judiciais e pela destruição da cidade de São João Marcos-RJ.

Changes in fish assemblage structure along a longitudinal gradient of the Paraíba do Sul River and Funil reservoir were studied to detect distribution patterns and the seasonal influence of the inflowing river. Fish were caught by gill nets in three zones (riverine, transition and lentic) during two seasons (dry and wet). A total of 3,721 individuals were captured, comprising five orders, 14 families, 27 genera and 33 species. Five species were non-native and amounted to 17.7% of the total number of individuals. The 10 most abundant species were used to assess spatial-temporal patterns. Plagioscion squamosissimus (Heckel, 1840), Oligosarcus hepsetus (Curvier, 1829) and Metynnis maculatus (Kner, 1858) were widely distributed in both seasons. Astyanax bimaculatus (Linnaeus, 1758), Cichla kelberi Kullander & Ferreira, 2006 and Geophagus brasiliensis (Quoy & Gaimard, 1824) had higher abundance in the dry season, occurring mainly in the lentic zone. By contrast, the benthopelagics Pimelodus maculatus La Cèpede, 1803 and Astyanax parahybae (Eigenmann, 1908) and the benthics Hoplosternum littorale (Hancock, 1828) and Hypostomus auroguttatus Kner, 1854 had higher abundance in the wet season, with the two first species occurring mainly in the riverine zone, and latter two species in the transition zone. The highest diversity for both seasons was recorded in the transition zone, which is an ecotone that allows the co-existence of both riverine and lentic species. A major shift in assemblage structure occurred along the longitudinal gradient due to changes in discharge of the inflowing river, with increased fish abundance in the riverine zone caused by increased habitat availability in wet season, and the reverse of this situation in the dry season.

Estudamos a dieta dos juvenis de Trachinotus carolinus (Linnaeus, 1766) em praias da Baía de Sepetiba (Rio de Janeiro, Brasil) entre janeiro de 2000 e abril de 2001. Procuramos avaliar a plasticidade trófica de peixes desta espécie ao longo de um gradiente espacial com diferentes níveis de exposição às ondas, sazonalidade, além de avaliar mudanças ontogenéticas na dieta. Os itens alimentares foram analisados através do índice de importância relativa (IIR), determinado pelos valores das frequências de ocorrência, de número e de peso. Os itens de maior importância foram do subfilo Crustacea, ordens Mysidacea, e o representante da ordem Decapoda Emerita brasiliensis (Schmitt, 1935), além de Cefalochordata, representado por Branchiostoma platae (Fitzinger, 1862). Na zona de maior exposição às ondas (praia de Barra de Guaratiba) e com substrato predominantemente arenoso, a dieta foi constituída principalmente por Emerita brasiliensis e Cirripedia, este último presente nos costões rochosos que limitam a praia; na zona de exposição intermediária (praia de Muriqui), houve um predomínio de Mysidacea e Branchiostoma platae; na zona mais protegida (praia de Itacuruçá), os itens de maior abundância foram Polychaeta, Mysidacea e Branchiostoma platae. Sazonalmente não ocorreu variação no uso de Mysidacea, enquanto Branchiostoma platae foi mais consumido durante o inverno, Polychaeta na primavera e Cirripedia e Emerita brasiliensis, no verão. Mysidacea foi o alimento predominante em todas as classes de tamanho, enquanto Polychaeta foi utilizado predominantemente por peixes menores que 20 mm de comprimento padrão e Emerita brasiliensis e Cirripedia foram consumidos principalmente por indivíduos maiores que 40 mm, somente na praia de maior exposição. O sucesso no uso de praias desprotegidas e zonas de arrebentação por esta espécie de peixe pode ser em parte devido à estratégia trófica oportunista, que utiliza uma ampla variedade de recursos disponíveis no ambiente.

We studied the diet of juvenile Trachinotus carolinus (Linnaeus, 1766) in sandy beaches of Sepetiba Bay (Rio de Janeiro, Brazil), between January 2000 and April 2001. We tried to evaluate the trophic plasticity of fish this species along a spatial gradient of wave exposure, seasonality, besides to evaluate ontogenetic changes in the diet. The Index of Relative Importance (IRI) was used to measure the food items, determined by their frequency of occurrence, numbers and weights. The subphylum Crustacea, mainly the order Mysidacea, Decapoda Emerita brasiliensis (Schmitt, 1935) and Cephalochordata, represented by Branchiostoma platae (Fitzinger, 1862) were dominant in the diet. In the most exposed zone (Barra de Guaratiba beach) with predominant sandy substrate, the diet was comprised mainly by Emerita brasiliensis and Cirripedia, this later item common in rocky shores at the beach edge; in the intermediate exposed beach (Muriqui beach), Mysidacea and Branchiostoma platae; in the most protected beach (Itacuruçá beach), Polychaeta, Mysidacea and Branchiostoma platae was predominant. No seasonal change was recorded for the use of Mysidacea, while Branchiostoma platae was the more consumed during the winter, Polychaeta in spring, Cirripedia and Emerita brasiliensis, in summer. Mysidacea was the predominate food in all size classes, while Polychaeta was used predominantly by fish smaller than 20 mm standard length (SL) and Emerita brasiliensis and Cirripedia, were consumed mainly by larger individuals than 40 mm in the most exposed beach only. The success in use of surf zones and sand beaches by this fishes species, it can be partly, due the opportunist trophic strategy that uses a wide variety of available resources on environmental.

Mudanças na estrutura da assembleia de peixes foram analisadas ao longo de um gradiente longitudinal do rio Paraíba do Sul e Reservatório do Funil. A hipótese testada foi a de que mudanças do ambiente lótico para o lêntico afetam a riqueza e a estrutura da assembleia de peixes que são moduladas pelas variações sazonais da pluviosidade. Coletas mensais padronizadas foram realizadas entre outubro de 2006 e setembro de 2007 em quatro zonas: 1) rio a montante do reservatório; 2) parte alta do reservatório; 3) parte baixa do reservatório, e 4) rio a jusante do reservatório. Os peixes foram capturados com redes de espera que ficaram em operação por 15 horas. Um total de 4.550 espécimes foi coletado, representando 35 espécies e 5 ordens. A maior riqueza e diversidade foram registradas na zona 2, a zona de transição entre rio e reservatório. Neste ecótono, espécies lóticas e lênticas se sobrepõem. Maior abundância e biomassa foram observadas no rio a montante do reservatório (zona 1), no entanto, não houve diferenças na estrutura da assembleia de peixes entre as zonas durante a estação chuvosa. Durante a estação seca, a estrutura da assembleia de peixes foi mais diferenciada entre as zonas, porém sem diferenças na abundância e biomassa. O fluxo sazonal do rio é o principal fator a influenciar a estrutura da assembleia de peixes ao longo do gradiente longitudinal rio-reservatório.

We analysed changes in the fish assemblage structure along a longitudinal gradient of the Paraíba do Sul River and Funil Reservoir. We tested the hypothesis that shifts from lotic to lentic environment affect the richness and structure of the assemblage which are modulated by seasonal rainfall changes. Standardised monthly samplings were carried out from October 2006 to September 2007 in four zones: 1) river upstream from the reservoir; 2) upper part of the reservoir; 3) lower part of the reservoir, and 4) river downstream from the reservoir. Fishes were caught using gillnets deployed for 15 hours. We collected a total of 4550 specimens, representing 35 species and 5 orders. The highest richness and diversity were recorded in zone 2, the transitional zone between river and reservoir. In this ecotone, lotic and lentic species overlap. Greater abundance and biomass was recorded in the river upstream from the reservoir (zone 1); however, there are no differences between the zones in the structure of assemblages during the wet season. During the dry season, the assemblage structure is more differentiated between zones, although no differences in abundance and biomass occur. The seasonal flow of the river is the major driving factor to influence the fish assemblage structure along the longitudinal gradient from the river to the reservoir.