Diet composition of Plagioscion squamosissimus (Heckel, 1840), a fish introduced into the Tietê River system

Plagioscion squamosissimus is a species from the Amazon basin that was introduced into the Tietê River system. The present study aimed to analyse the feeding habits of this species in Bariri Reservoir and to verify the possible occurrence of ontogenetic changes in its diet composition. The samples were gathered in four periods of the year: February, June, September and November 2003. The fish were gathered with different fishing net meshes in three different reservoir portions. The alimentary items found in the stomachs were identified to the lowest possible taxonomic level and had abundance, occurrence frequency, volume and biomass determined. The Alimentary Index (IAi) was calculated for each alimentary item consumed by "corvina" for each studied period. Comparisons among the diet of different size classes of P. squamosissimus were done using the similarity coefficient of Jaccard and the Cluster Analysis (UPGMA). The Friedman proof was performed to verify if there is a significant ontogenetic variation in the species diet and changes in the consumption of different alimentary categories by P. squamosissimus among the sampled periods. P. squamosissimus presented a piscivorous feeding habit, although other items were also consumed. The biggest values of IAi were obtained for the alimentary item fish in the months of June (0.47) and November (0.39). The item Ephemeroptera (Campsurinae) was the most representative in February (0.30) and June (0.45). Despite the fact that P. squamosissimus consumed an ample spectrum of alimentary items, the ontogenetic changes were evident through the exploration of aquatic insects by the younger classes and by a diet mainly composed of fish in adult individuals. The alimentary plasticity of P. squamosissimus evidenced in this study might have contributed to the success of this species in Bariri Reservoir

Reproduction of the fish community of Passa Cinco Stream, Corumbataí River sub-basin, São Paulo State, Southeastern Brazil

The aim of this work was to evaluate the reproduction (verifying if there was reproductive activity and, if so, with what intensity) of the most abundant species of the fish community in Passa Cinco stream, in relation to the dry and wet season periods and to the longitudinal gradient, through the application of the reproductive intensity index (RII). The sample collection was carried out during one year with six samplings (May, July, September and November 2005, and January and March 2006) in five different points of Passa Cinco stream, contemplating sites of orders two to six. The following fishery equipment was used: a sieve, electric fishery equipment, gill nets and fish-traps. The values of the reproductive intensity index for the dry period were 2.86 and for the wet season 3.17, which indicates the wet season (November to March) as the period when most of the species reproduced. The values of the index for collection point were: 0.78 for site 1, 3.56 for site 2 and 2.89 for site 3. Site 2, which presented the highest value, was the main reproduction place for most of the species. The adults' prevalence in the analysed species suggests, in an isolated way, that those species use the system as a reproduction area. However, when that information was crossed with the values of RII, when intermediate values were considered, it is possible to state that the system is used by the species as much as a reproduction area as a feeding area