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The ichthyofauna of the Manantiales (35°0234S; 58°1937W) and El Portugués (35°0416S; 58°2609W) streams, both of them pertaining to the high basin of the Samborombón River, in the Province of Buenos Aires, Argentina, was studied. Abundance, specific richness, diversity and temporary distribution were considered throughout an annual cycle. The specific diversity between both streams was compared and the physical and chemical parameters of the environment analizad. In total 8595 specimens were captured, pertaining to 20 species, 11 families and 5 orders. The order Characiformes was the most widely represented with 10 species and a relative abundance of 50%, followed by the order Siluriformes with 6 species and a relative abundance of 30%. The specific richness in the Manantiales was of 20 species, the annual diversity index was 1.42 and the uniformity index was 0.58. The specific richness in El Portugués was of 17 species, the annual diversity index was 1.51 and the uniformity index was 0.64. Differences in the composition of dominant species were observed. The diversity values are similar to that recorded in Pampasia and southern Brazil streams.

Over the past few decades, land-use changes through conversion of global forest cover to exotic plantations is contributing to both habitat and biodiversity loss and species extinctions. To better understand human influences on ecosystem, we use diet composition from introduced Rainbow Trout Oncorhynchus mykiss as indicator of potential changes in the composition of stream-macroinvertebrates due to land use changes from native to exotic vegetation (eucalyptus plantations) in southern Chile. Water quality variables, aquatic macroinvertebrates and Rainbow Trout diet were studied in 12 sites from mountain streams located in two watersheds including one dominated by native riparian vegetation and the other dominated by exotic vegetation. As expected, richness and abundance of macroinvertebrates were clearly higher at sites in native forest than in those with exotic vegetation. Collector-gatherer was the most abundant functional feeding group, but there was no statistical difference in the functional composition between the two watersheds. Differences in in-stream macroinvertebrate availability was more higher correlated with changes in Rainbow Trout diets. Specifically, taxa consumed from the watershed dominated by native forests was higher than from the watershed with exotic vegetation. Additional environmental variables showed statistical differences between watersheds. The exotic vegetation sites had the highest concentrations of dissolved solids, suspended solids, nitrates, chlorides and sulphates. Our findings show that macroinvertebrate assemblage structure and trout diets can be altered by changes in riparian vegetation. The absence of specific macroinvertebrate taxa in streams with exotic vegetation was captured by the composition of trout diets. This suggest that Rainbow Trout diets can be a good biological indicator of land use practices and thus, diet can be used as a rapid and effective tool for evaluate environmental quality. Our findings provide insights about the design of aquatic monitoring programmes to improve detection of anthropogenic impacts in streams in South America and elsewhere.

The reproductive period of the Glandulocaudine Pseudocorynopoma doriai was determined by the analysis of 240 females, 90 males and 138 immature individuals collected monthly in the Manantiales and the El Portugue´s rivers. The reproductive period is seasonal, occurring from late winter to mid-summer, with another reproductive peak of smaller magnitude in early autumn. The mean monthly GSI in males has a significant correlation with rainfall. Other analyzed environmental variables, including temperature, photoperiod, pH and conductivity, did not show a correlation with the mean monthly GSI in females and males. First maturity in females was reached within the 42-43 mm standard length class. Like other Glandulocaudines from southern Brazil, males initiate sexual maturation before females, which implies an adaptive advantage in that this would enable females to spawn under optimal environmental conditions. The mean absolute fecundity was 1286.42 oocytes (SD ¼ 496.9083); the mean relative fecundity was 0.5070 (SD ¼ 0.1333) oocytes by milligram body weight.

Diet and ecomorphology of the ichthyofauna of Manantiales stream, Buenos Aires province, Argentina. the present study addresses the correlation between diet and morphology of 19 fish species that inhabit the Manantiales stream at the headwaters of the samborombón river, Buenos Aires province, Argentina. the species were classified into four trophic groups: carnivores, omnivores, insectivores and detritivores-alguivores. twelve ecomorfologic attributes related to habitat use and feeding patterns were analyzed to distinguish ecomorphologic groups of species with the food consumed. Univariate and multivariate analysis techniques were used to determine groups of species using the ecomorfologic and diet attributes as descriptors. Carnivores were associated with well developed head, mouth, pectoral and caudal fins and usually presenting compressed bodies. omnivores were a more heterogeneous group. nektonic forms of this group were associated with a compressed body, lateral eyes and relatively small size of the pectoral fins and caudal fins; nektobentonic forms were associated with small mouth, fusiform body and long caudal peduncle; benthic forms were related to depressed body, dorsal eyes, ventral mouth and long digestive tract. the only nektonic species consuming insects on the surface is characterized by a strongly compressed body, lateral eyes, tail and big wide mouth facing up. the detritus-alguivores had a long digestive tract, mouth ventral or terminal and long caudal fin. the significant relationship between diet and ecomorphology allows to sustain that fish with similar diets converge towards common ecomorfologicic attributes.Key words: diet, morphology, multivariate analysis, samborombón river, Argentina.Resumen: se estudio la correlación entre dieta y morfología de 19 especies de peces del arroyo Manantiales, cabecera del río samborombón, provincia de Buenos Aires, Argentina. Las especies fueron clasificadas en cuatro grupos tróficos: carnívoros, omnívoros, insectívoros y detritívoros-alguívoros. se analizaron 12 atributos ecomorfológicos relacionados con el uso del hábitat y la alimentación con el fin de distinguir patrones ecomorfológicos de las especies y de las especies con el alimento consumido. se utilizaron técnicas de análisis univariado y multivariado para determinar agrupamientos de especies utilizando los atributos ecomorfológicos y la dieta como descriptores. Los carnívoros se relacionaron con un buen desarrollo de cabeza, boca, aletas caudal y pectoral; y en general con cuerpos comprimidos. Los omnívoros constituyeron un grupo más heterogéneo. Las formas nectóni-cas de este grupo se relacionaron con un cuerpo comprimido, ojos laterales y tamaño relativamente pequeño de las aletas pectorales y aleta caudal; las formas nectobentónicas se relacionaron con boca pequeña, cuerpo fusiforme y pedúnculo caudal largo; y las formas bentónicas, con cuerpo deprimido, ojos de posición dorsal, boca ínfera y tubo digestivo largo. La única especie nectónica consumidora de insectos sobre la superficie ...

IntroduccIónEl orden characiformes es uno de los más diversos de peces neotropicales, presentando una gran variedad de formas, comportamientos y adaptaciones al medio (Lowe-Mcconnell, 1987), siendo la familia characidae la que posee mayor número de especies. Los representantes de la subfamilia Glandulocaudinae, alrededor de 50 especies, se distribuyen desde el sur de costa rica hasta Ecuador en cursos de agua que drenan al Pacífico; y desde trinidad y norte de Venezuela hasta el norte de la provincia de Buenos Aires, Argentina, de pendiente atlántica (Weitzman, 2003).Pseudocorynopoma doriai Perugia, 1891 es el glandulocaudino que presenta la distribución más austral. Se la encuentra desde el sur de Brasil hasta el norte de la Pampasia, en la cuenca del río Salado, y en la cuenca paranoplatense. (ringuelet et al., 1967; Almirón et al., 1992;López et al., 2001). Los miembros de la subfamilia Glandulocaudinae presentan especies con inseminación. Este grupo se caracteriza por el marcado dimorfismo sexual y por la presencia en los machos de una glándula caudal con células activas que secretan feromonas durante el cortejo, lo que facilita la inseminación (nelson, 1964 (IrI). the results obtained indicate a diet with no significant differences throughout the year, consisting mainly of aquatic insects, allochthonous insects and spiders. the analysis shows that while there were no significant differences in diet at differents range length of this species, individuals less than 42 mm standard length, consumed a greater number of insects of terrestrial origin. the results allow to characterize Pseudocorynopoma doriai as a generalist insectivorous species for this stream of Pampasia.Key words: Fish, Pseudocorynopoma doriai, food, Argentina.Resumen: Se describe la dieta de la mojarra de velo, Pseudocorynopoma doriai, en el arroyo El Portugués (58° 26' 30'' S -35° 04' 24'' W), perteneciente a la alta cuenca del río Samborombón, provincia de Buenos Aires. Para tal fin, se realizaron muestreos mensuales desde mayo de 2004 hasta abril de 2005. Para el análisis de los contenidos estomacales se utilizaron métodos de frecuencia, porcentaje volumétrico, porcentaje numérico e índice de importancia relativa (IrI). Los resultados obtenidos indican una dieta sin diferencias significativas a lo largo del año, constituida básicamente por insectos acuáticos, insectos alóctonos y arañas. El análisis demuestra que si bien no se encontraron grandes diferencias en la dieta de esta especie según la talla, los individuos menores de 42 mm de longitud estándar consumieron una mayor cantidad de insectos de origen terrestre. Los resultados permiten caracterizar a Pseudocorynopoma doriai como una especie insectívora generalista para este arroyo de la Pampasia.

Algunos aspectos biológicos deAbstract: Some aspects of biology of Bryconamericus Iheringii (Ostariophysi: Characidae) in two streams in the high basin of the Samborombón river, Argentina. This study analyzed the following aspects of the Bryconamericus iheringii population structure: abundance patterns, condition factor, male-female sex ratio, relation between weight and length, and reproductive period.

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