Loss of connectivity in impounded rivers is among the impacts imposed by dams, and mitigation measures such as fish passages might not accomplish their purpose of reestablishing an efficient bi-directional gene flow in the fish populations affected. As a consequence, fish populations remain fragmented, and a new interpopulational structure may develop, with increased risk of reduced genetic diversity and stochastic extinction. In order to evaluate the effects of the Gavião Peixoto Dam, which was constructed almost a century ago on the Jacaré-Guaçu River in the Upper Paraná River basin, Brazil, a comparative morphometric study was undertaken on the populations of the Neotropical migratory characid fish Salminus hilarii living up-and downstream of this dam. Population dynamics, spatial segregation, and habitat use by different age classes were monitored for 2 years. We found that segregation caused by the dam and long periods with no efficient connection by fish passages have led to fragmentation and interpopulational structuring of S. hilarii, as revealed by canonical variable analysis of morphometric features. The fish populations occupying the up-and downstream sections have succeeded in performing short-distance reproductive migrations in the main river and tributaries, have found suitable habitats for completing their life cycle, and have been able to maintain distinct small-sized populations so far.

The Paranapanema River is a major tributary of the upper Paraná river basin. Eleven hydropower dams regulate its main course, but no study has investigated fish diversity in these impoundments at the basin-scale. The present study investigated spatial patterns of richness, composition, and abundance of native (non-migratory and migratory) and non-native fishes in the cascade of reservoirs along the Paranapanema River. The study is based on data collected from 34 independent studies conducted in nine reservoirs (47 samples). The compilation recorded 161 species, being 111 native (14 migratory) and 50 non-native. Total richness ranged between 56 and 112 species/reservoir, with a mean of 72 (49.9 non-migratory, 8.1 migratory and 14 non-native). The number of non-migratory species showed no spatial trend along the cascade system, but migratory and non-native richness increased toward downstream reaches. We also observed spatial variation in species composition along the cascade system, but some non-native fishes were widely distributed. Migratory fishes showed low relative abundance (usually < 10%), while non-native species were common and more abundant, especially in reservoirs downstream. Our results revealed a high diversity of fishes in the cascade of impoundments, but indicated that migratory fishes are rare, while non-native species are common or dominant.

Aim: To evaluate the primary productivity of the phytoplankton in the Lake Monte Alegre, southeastern Brazil, and the factors that influence its fluctuations, experiments were carried out in the lake and in mesocosm; Methods: Primary productivity rates were measured using the 14 C technique, in experiments carried out monthly in the lake, during one year, and in two mesocosm experiments, one in the winter and another in the summer. Other factors also analyzed were temperature, dissolved oxygen, pH, electrical conductivity, chlorophyll-a, alkalinity, nutrients, and nitrogen limitation. Hypotheses on the influence of grazing and excretion by zooplankton and fish on phytoplankton properties were tested in two mesocosm experiments; Results: Higher PP in the water column of the lake occurred in the transition periods, when thermal stratification is unstable, and lower PP in the cool season (frequent mixing) and in mid-summer (more stable stratification). The limiting factor in the cool season seems to be mainly temperature and in mid-summer lower light intensities, due to higher rainfall and overcast, N limitation and physical disturbances caused by storms. PP was not influenced by the zooplankton in the experiment I, despite the effect of grazing on other phytoplankton properties. The excretion by the phytoplanktivorous fish (adults of Tilapia rendalli) enhanced PP in the experiment II, outweighing grazing on the phytoplankton; Conclusions: We suppose that the preponderant factors which affected primary productivity in the lake were physical and chemical ones, biotic factors having a secondary role. The thermal behavior of the lake, which is warm discontinuous polymictic, governs nutrient losses and releases, influencing PP in addition to other factors related to seasons.Keywords: primary productivity, assimilation rates, chlorophyll-a, thermal behavior, bottom-up and top-down control.Resumo: Objetivo: Para avaliar a produtividade primária do fitoplâncton e os fatores que influenciam suas flutuações foram feitos experimentos no Lago Monte Alegre e em mesocosmos; Métodos: Foram feitos experimentos mensais de produtividade primária (PP), usando o método do 14 C, no lago, durante um ano, e em dois experimentos em mesocosmos, um no inverno e outro no verão. Outros fatores medidos foram temperatura, oxigênio dissolvido, pH, condutividade elétrica, clorofila-a, alcalinidade, nutrientes e limitação de nitrogênio. Foram testadas hipóteses sobre a influência do consumo e excreção do zooplâncton e peixes sobre o fitoplâncton em dois experimentos realizados em mesocosmos; Resultados: Maior PP na coluna de água do lago ocorreu nos períodos de transição, quando a estratificação é instável, e menor PP na estação fria (circulação freqüente) e no meio do verão (estratificação mais estável). O fator limitante na estação fria parece ser principalmente a temperatura e no meio do verão as intensidades luminosas mais baixas, devido a maior pluviosidade e tempo nublado, limitação de nitrogênio e perturbações físicas causadas po...

The conservation of diverse and well-distributed fish taxa, as the genus Leporinus, relies intrinsically on the knowledge of the ecological attributes of its representatives. Aiming to increase this knowledge, studies on diet and ecomorphology are ideal to provide important information about species ecology. Thus, this study aimed to analyze aspects of feeding ecology of L. reticulatus, from the upper Rio Juruena, Mato Grosso State, Brazil. The diet of specimens in different ontogenetic stages was compared, as well as their teeth morphology and ecomorphological attributes. Leporinus reticulatus presented omnivorous diet, with higher consumption of invertebrates by smaller specimens (younger ones), and gradual introduction of plant items in larger specimens (older ones). The items consumed by the individuals and the ecomorphological attributes indicated that the species is generalist and opportunistic, besides its association with the river bottom, evidencing a benthic feeding behavior. This species presents a gradual ontogenetic modification in teeth shape and mouth positioning, ranging from a terminal mouth with tricuspid teeth, in smaller specimens, to an inferior mouth with spatula shaped teeth with no cusps, in larger specimens. The ecomorphological attributes indicate an increasing swimming efficiency, and ability for performing vertical displacements, along the ontogenetic development, which in addition to the morphological ontogenetic alterations in the buccal apparatus, contributes to a better ability to explore another niches. KEYWORDS: Neotropical ichthyofauna, freshwater fish, trophic ecology, ontogenetic morphological variation. Dieta e ecomorfologia de Leporinus reticulatus (Characiformes: Anostomidae) do alto Rio Juruena, MT, Brasil: alterações ontogenéticas relacionadas à ecologia alimentar RESUMO A conservação de táxons de peixes de grande diversidade e amplamente distribuídos, como o gênero Leporinus, depende intrinsicamente do conhecimento de atributos ecológicos de seus representantes. Objetivando o aumento deste conhecimento, estudos que abordam a dieta e a ecomorfologia são ideais para prover informações importantes sobre a ecologia de espécies. Assim, este trabalho teve como objetivo analisar aspectos da ecologia alimentar de L. reticulatus originários do alto Rio Juruena, estado do Mato Grosso, Brasil. Foi comparada a dieta de espécimes em diferentes estágios ontogenéticos, assim como a morfologia dos dentes e atributos ecomorfológicos. Leporinus reticulatus apresentou dieta onívora, com maior consumo de invertebrados pelos espécimes de menor porte (mais jovens), e introdução gradual de itens vegetais por espécimes de maior porte (mais velhos). Os itens consumidos pelos indivíduos e os atributos ecomorfológicos indicaram que esta espécie é generalista e oportunista, além de sua associação com o fundo do rio, evidenciando um comportamento alimentar bentônico. Esta espécie apresenta modificação ontogenética gradual no formato dos dentes e posição da boca, variando de uma boca termina...