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The Suquía River basin (Córdoba, Argentina) is under a strong negative impact due to multiple sources of anthropic pollution. The main goal of our study was to evaluate if variations in the water quality of Suquía river basin affect the reproductive biology of Cnesterodon decemmaculatus and determine if the responses provided by the species can be considered as biomarkers of river quality. This assessment was performed through the measurement of morphological, histological and somatic parameters in adult males collected at four sampling sites during the beginning and the end of the breeding season. The water quality evaluation carried out through the estimation of a water quality index (WQI) and pesticides concentrations in water, revealed a pollution gradient along the studied basin. The same variation pattern was registered for the somatic index. In addition, the analysis of the morphology of the male copulatory organ (gonopodium) showed that individuals collected at Córdoba city had the lowest Gonopodium-Somatic Index (Gonop-SI) value, while those sampled at the most polluted site showed abnormalities in the small structures of the gonopodium. On the other hand, few histological alterations were found in the liver whereas no alterations were found in gonads along the river. The results obtained allowed us to characterize the environmental conditions of the studied basin and demonstrated the water quality deterioration along the Suquía River.

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ABSTRACT. Characterization of Culicidae larvae (Diptera) consumption in two species of native fish in the central zone of Argentina. Mosquitoes represent a threat to human health and animals because they act as vectors of several diseases. Native fish species are potential candidates to be considered for biological control populations of mosquitoes. Tests of half-hour and 24-hour consumption of Culex pipiens (Linnaeus, 1758) larvae by Cnesterodon decemmaculatus (Jenyns, 1842) and Jenynsia multidentata (Jenyns, 1842) were carried out, measuring the standard length, mouth width and weight in individuals of the two species of fishes. In both tests J. multidentata consumed more C. pipiens than C. decemmaculatus, being C. decemmaculatus female consumption higher than male consumption (and equal than both sexes of J. multidentata in the 24-hour test). These results remained unchanged when making comparisons of absolute or relative consumption in the half-hour test, but when consumptions relative to weight were compared no difference between species was found in the 24-hour test. Regression analysis between morphometric variables and weight vs. consumption rates showed low explanatory value for the half-hour test, while in the 24-hour test these variables had higher explanatory value, especially for the mouth width. Finally, a half-hour test was performed over C. decemmaculatus females using C. pipiens and Aedes aegypti (Linnaeus, 1742) larvae and it showed a strong preference for the latter ones. This work allowed us to observe that there are large differences in consumption rates of C. pipiens larvae between the fish species under study in short periods. Differences are attenuated when consumption times are longer and may even disappear when weight is taken into account. KEYWORDS.Cnesterodon decemmaculatus, Jenynsia multidentata, biocontrol, mosquito larvae. RESUMEN.Los mosquitos representan una amenaza para la salud del hombre y de los animales debido a que actúan como vectores de distintas enfermedades. Especies de peces nativos son potenciales candidatos a tenerse en cuenta para control biológico de poblaciones de culícidos. Experiencias de consumo de media hora y de 24 horas por Cnesterodon decemmaculatus (Jenyns, 1842) y Jenynsia multidentata (Jenyns, 1842) se llevaron a cabo con larvas de Culex pipiens (Linnaeus, 1758), midiéndose longitud estándar, ancho de boca y peso en individuos de las dos especies. En ambas pruebas, J. multidentata consumió más C. pipiens que C. decemmaculatus, consumiendo las hembras de esta última especie más que los machos (e igual a ambos sexos de J. multidentata en la prueba de 24 horas de duración). Estos resultados no variaron cuando se compararon tantos consumos absolutos o relativos para las pruebas de media hora, sin embargo cuando se compararon los consumos relativos al peso no se encontraron diferencias entre las especies para las pruebas de 24 horas. Análisis de regresión entre las tasas de consumo versus las variables morfométricas y el peso mostraron poco valor explicati...

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