Abstract
Invertivores fishes are an important component of neotropical streams and they represent a link between aquatic invertebrates and piscivorous species. This study evaluated the breadth diet and interspecific food overlap of nine invertivores fish species during three consecutive hydrological phases: falling (December/07, January/08, February/08 and March/08), low (April/08) and rising waters (June/08), in two sections of a Venezuelan neotropical stream, which were located at different elevation, high watershed (HW) and low watershed (LW). The fishes were collected with a beach seine (5mm mesh) between 8:00 and 11:00 hours. The diet of each species was evaluated using an index of relative importance (IRI), which includes as variables the number, weight and occurrence frequency of food items consumed. The Levin' index (B ) and Morisita (IM) were used to estimate the breadth diet and interspecific food overlap, respectively. All estimations were made using the numeric proportion of preys. Nine fish species were captured, eight Characiformes, of which three were captured in HW (Knodus deuteronoides, Creagrutus bolivari and C. melasma) and five in LW (Thoracocharax stellatus, Moenkhausia lepidura, Cheirodon pulcher, Ctenobrycon spilurus and Aphyocharax alburnus), and one Cyprinodontiformes (Poecilia reticulata), which was also found in HW. In HW aquatic insects were the main resource consumed by fishes while plant material and terrestrial arthropods were secondary resources. In LW the fishes ingested all of these items in addition to zooplankton (Copepoda, Cladocera and larval stages of Decapoda). However, there was a temporal replacement with a predominance of zooplankton in falling and low water. In general, the breadth diet decreased during the falling water in both sections and increased in rising water. However, the average breadth diet was higher in HW. The interspecific food overlap was high in HW while low values were more frequent in LW and its temporal variation was opposed in both sections during almost all the sampling period.
Highlights
Incluyó a Ephemeroptera (9.8%), Artrópodos terrestres (5.5%), Coleoptera (4.5%), Diptera (3.2%), Odonata (2.5%) y Hemiptera (2.5%)
La sobreposición entre C. melasma y K. deuteronoides tendió a ser menor ya que fueron más frecuentes los valores menores al 60%, sin embargo, también fue alta al inicio de descenso y en aguas bajas
La sobreposición interespecífica de dieta fue alta en SA mientras que en SB fueron más frecuentes los valores bajos y en casi todo el registro su variación temporal fue opuesta en ambas secciones
Summary
Area de estudio: Se evaluaron dos secciones del cauce principal del río Orituco, ubicado en el centro-norte de Venezuela. La dieta de las especies en SA estuvo constituida por invertebrados acuáticos (insectos, gastrópodos y ostrácodos), artrópodos terrestres y material vegetal alóctono. Los artrópodos terrestres fueron un componente importante en C. bolivari y K. deuteronoides, mientras que en C. melasma y P. reticulata su consumo fue insignificante. El consumo promedio de invertebrados terrestres fue muy bajo en C. melasma, representó cerca del 15% del consumo total en C. bolivari y K. deuterodonoides y no fue una presa depredada por P. reticulata. Los cladóceros fue el grupo del zooplancton más depredado en las cuatro especies y sólo en A. alburnus los copépodos llegaron a representar un porcentaje alto. M. lepidura fue la especie que consumió el mayor número de tipos de presas y en casi la totalidad del registro consumió, de manera simultánea, presas del bentos, plancton, artrópodos terrestres y material vegetal alóctono. En este caso sólo un tipo de presa (Trichoptera) representó el 72% de todas las consumidas, que en este mes índice de importancia relativa IIR (%)
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