Resumen:
The native European freshwater cyprinid fish, common bleak Alburnus alburnus (Linnaeus, 1758), is an invasive non-native fish in the Iberian Peninsula, where it threatens the valuable endemic fish fauna. Despite the bleak's invasive status, there is a dearth of studies on the biological traits of non-native populations in Europe's Mediterranean region, and the present study aimed to compare bleak growth and reproductive traits across the principal rivers of Iberia with those from a native 'reference' bleak population in France. Non-native bleak from the River Tagus had the highest back-calculated total lengths (TLs), growth rate and body condition, but the lowest reproductive investment and smallest egg size of all studied populations. Whereas, these latter two traits were the highest in the River Ebro, where fecundity was the lowest for all Iberian rivers. The youngest age and the smallest TL at maturity were observed in the River Ebro. The River Segura had the lowest back-calculated TLs and growth rate, the highest fecundity and proportion of females, and the oldest age at maturity. Population traits of bleak in the River Saone (the native 'reference' population) were generally different from those in Iberian rivers, except for the River Ebro. This wide inter-population variability contributes to the species' successful establishment in novel habitats.