CONICET | Buscador de Institutos y Recursos Humanos

Ephemeral ponds in the Pampasic Region, southeast Entre Ríos, Argentina were studied during a three years period in order tounderstand the lling/drying cycle, its relationship with climate variables and its inuence in life history traits and populations of theAustrolebias species inhabiting them. Three species of this genus were recorded in the area: A. alexandri, A. nigripinnis and A. bellottii.Climate variables (temperature, rain, etc.) were obtained daily from a meteorological station nearby. Monthly, 8 ponds were registeredin three areas. Fish were netted with standardized sampling procedures, identied, sexed, measured and returned to the pond at the endof the sampling. Water depth, pond size, and chemical parameters (pH, secchi disc, conductivity, temperature) were measured. Pondlling generally occurs at the end of summer between February to March. Hatching of the eggs seems to occur in a single event (onecohort) since no differences in size structure of the populations were detected in this study. During winter, low rains induce the drying ofthe ponds, which may get completely or partially dried by August. During this period a considerable decrease in the number ofindividuals is observed. Ponds may present one single ?cycle? per year or two (may be more, but not observed in this study). On springrains and temperature increases and water volume increases until maximum levels. Sex ratio was variable among species and places.Males show higher mortality levels than females. Growing of individuals was positively correlated with temperature. Winter represents ahigh mortality period, probably due to a combination of factors such us low temperature (depress of the immune system), overcrowdingby low water levels and consequently increased aggressive interactions and food competition. Further information will be presented inthis work.