Dietary traits of invasive bleak Alburnus alburnus (Actinopterygii, Cyprinidae) between contrasting habitats in Iberian fresh waters

The bleak Alburnus alburnus (L., 1758) is a limnophilic fish native to most of Europe. This cyprinid species is a successful invader in the Iberian Peninsula, where it threatens the highly endemic fish fauna. However, studies on bleak autoecology are scarce in this region, with few data on foraging strategies. The aim of this work was to compare the dietary traits of bleak populations between contrasting habitats in Iberian fresh waters. For this purpose, bleak were seasonally collected from the small River G,vora and the Sierra Brava Reservoir (Guadiana River Basin, southwestern Spain). As percentages of occurrence and ingested mass, plant material and planktonic Crustacea were the most important food categories in the river and the reservoir, respectively. The intake of pelagic prey was higher in the reservoir, especially during summer. Benthic prey, plant material and detritus were more consumed in the river, especially benthos and detritus during spring, whereas plant intake decreased during this season. Shannon index, as a measure of trophic diversity, was higher in the reservoir, except for spring. Overall results suggest that this wide trophic plasticity will facilitate the bleak invasion process throughout Mediterranean Europe, which poses a serious risk to its highly valuable native fish fauna.