This study was aimed at evaluating the infection levels of Austrodiplostomum compactum metacercariae in 378 specimens of Plagioscion squamosissimus ('corvina' or 'pescada branca') from the Nova Avanhandava reservoir, low Tietê River, São Paulo State, Brazil. High prevalence, mean intensity of infection and abundance were observed in P. squamosissimus during most of the study, with the exception of March 2004. The relative condition factor (Kn) did not differ between parasitized and non-parasitized fish. A statistically significant positive correlation was observed between host standard length and intensity of infection. The analysis of biotic and abiotic variables showed that no abiotic variable correlated with parasitic infection levels. Moreover, P. squamosissimus status was demonstrated to be unaffected by A. compactum metacercariae infection.

This study aimed to evaluate the infection by the Austrodiplostomum compactum metacercariae in fishes from the Nova Avanhandava Reservoir, low Tietê river, São Paulo State, Brazil. The parasites were collected from eye (aqueous and vitreous humor), fixed in AFA solution and stained with carmine. The morphometric analysis was performed using a computerized system for analysis of images QWin Lite 2.5 (Leica). Prevalence, mean intensity of infection and abundance of infected fish were calculated. Of the 22 species of fish registered, five were infected by metacercariae: Hoplias malabaricus, Metynnis maculatus, Plagioscion squamosissimus, Satanoperca pappaterra and Schizodon nasutus. Of the 627 fish evaluated, 34% were infected. A higher prevalence was observed in P. squamosissimus and S. pappaterra. Schizodon nasutus and M. maculatus are new hosts reported for A. compactum metacercariae. RESUMO. Infecção por metacercárias de Austrodiplostomum compactum em peixes doReservatório de Nova Avanhandava, rio Tietê, Estado de São Paulo, Brasil. Avaliou-se a infecção por metacercárias de Austrodiplostomum compactum em peixes do Reservatório de Nova Avanhandava, baixo rio Tietê, São Paulo, Brasil. Os parasitos foram coletados nos olhos (humor aquoso e vítreo), fixados com solução de AFA e corados com carmim. A análise morfométrica foi realizada por meio de sistema computadorizado de análise de imagem QWin Lite 2.5 (Leica). A prevalência, intensidade média de infecção e a abundância média dos peixes infectados foram calculadas. Das 22 espécies de peixes capturadas, cinco estavam infectadas por metacercárias: Hoplias malabaricus, Metynnis maculatus, Plagioscion squamosissimus, Satanoperca pappaterra e Schizodon nasutus. De um total de 627 peixes avaliados, 34% estavam infectados. Alta prevalência foi observada em P. squamosissimus e S. pappaterra. Schizodon nasutus e M. maculatus são novos hospedeiros registrados para metacercárias de A. compactum. Palavras-chave: Diplostomidae, trematódeo, novos hospedeiros, olho, parasito.

In this study, the inverted trophic hypothesis was tested in the freshwater fish communities of a reservoir. The distribution of fish species in three freshwater habitats in the Jurumirim Reservoir, Brazil, was examined using both species richness and the relative proportions of different trophic groups. These groups were used as a proxy for functional structure in an attempt to test the ability of these measures to assess fish diversity. Assemblage structures were first described using non‐metric multidimensional scaling (NMDS). The influence of environmental conditions for multiple fish assemblage response variables (richness, total abundance and abundance per trophic group) was tested using generalised linear mixed models (GLMM). The metric typically employed to describe diversity; that is, species richness, was not related to environmental conditions. However, absolute species abundance was relatively well explained with up to 54% of the variation in the observed data accounted for. Differences in the dominance of trophic groups were most apparent in response to the presence of introduced fish species: the iliophagous and piscivorous trophic groups were positively associated, while detritivores and herbivores were negatively associated, with the alien species. This suggests that monitoring functional diversity might be more valuable than species diversity for assessing effects of disturbances and managements policies on the fish community.

This paper focuses on to evaluate the importance of a free stretches upstream of a Neotropical reservoir for the maintenance of Schizodon intermedius populations, a medium size migratory species and important fisheries resources. Quarterly samplings were carried out in 8 sampling sites, distributed in Jurumirim Reservoir and two tributaries upstream reservoir. Reproductive, populational and feeding strategies were used to evaluate the importance of each sample area in the biological cycle of this species. Results showed that S. intermedius makes different uses of the sites. In the rainy season, individuals in the lower areas presented higher condition factor and average repletion degree of stomach, assuming that are used for growth and feeding and; in the upper areas, higher size and GSi values, suggesting that are reproductive area. We conclude that Schizodon intermedius uses lentic areas to gain energy in dry season, and in the rainy season, uses this energy to migrate to lotic stretches to reproduction. The stretches upstream free of dam are essential for this migratory species maintain viable populations in an environment impaired by dams.

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