The aim of the study was to examine the ecology of Leuciscus pyrenaicus in intermittent streams in the middle reaches of the Guadiana basin, in southern Portugal, and examine the life history strategies this species adopts to survive the harsh environment conditions. Differences in growth and reproductive biology in three tributaries (Xévora, Caia and Degebe) were examined. L. pyrenaicus contributed up to 12% by number to the fish community, although each population was dominated by small individuals. Males up to five years of age and females up to seven years were caught. Females attained a greater size and age than males. The fastest growth rate was found in the Xévora river, where this species dominated the community structure and its “preferred” habitat characteristics were evident, i.e., moderately flowing water and coarse substrate. Changes in the gonadosomatic index (GSI) for sexually mature males and females suggest that gonad maturation occurs from October to April, and the spawning period is between April and July. Females from the Xévora river were more fecund and this was linked to the less harsh conditions found in this river. The species exhibits an r-selected life history strategy to survive the extreme environmental conditions in intermittent streams in the Guadiana basin.