Abstract
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.
Highlights
The presence of humans in natural environments leads, in practically all cases, to the introduction of animal and plant species, whether intentionally or accidentally
The aim of the present study was to characterise the food consumed by Plagioscion squamosissimus (“corvina”) and to determine whether there are changes in the items consumed attributable to ontogenetic changes, in Bariri Reservoir, Middle Tietê River basin, São Paulo State, Brazil
On the basis of the results obtained in Bariri reservoir, P. squamosissimus can be considered a fish of piscivorous feeding habit
Summary
The presence of humans in natural environments leads, in practically all cases, to the introduction of animal and plant species, whether intentionally or accidentally. Fishes are the most frequently introduced species, being transplanted from one hydrographic basin to others, in the same or even different continents (Rocha et al, 2005). Plagioscion squamosissimus (Heckel, 1840), native to the Amazon basin, was introduced in São Paulo in 1966 by the Hydroelectric Company, initially into the rivers Pardo, Grande and Paraná, as well as the Ilha Solteira and Jupiá reservoirs, from which they colonised the Tietê River reservoirs (Braga, 1998; Agostinho and Júlio Jr., 1999). Some introduced species may hybridise with native closely related species, competing for food and space for reproduction. They can carry disease agents (pathogens and parasites) (Rocha et al, 2005). Competition for food is, the main way in which introduced species affect native ones (Agostinho et al, 1994)
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