Leuciscus cephalus

The Ebro catchment has the highest richness of autochthonous limnetic species in the Iberian Peninsula [51]. Salaria (blennius) fluviatilis, is common at the main channel and tributaries, and Chondrostoma toxostoma only occurs at the tributaries. Leuciscus cephalus is a fish of narrow distribution, found only at the Ebro river basin and other small catchments of NE Spain. Salmonids are common at the headwaters one species is native Salmo trutta and two introduced others, Salmo gairdneri and Salvelinus fontinalis. Part of the autocthonous species are endemic, for example the cyprinids Barbus graellsii and Barbus haasi, the cobitid C. calderoni with scattered and scarce populations [52] and A. iberus. 

The occurrence of fishes in streams is considerably influenced by water pollution. A species which is very resistant against putrefactive pollution is Leuciscus cephalus, in contrast to the majority of salmon-like fish, for example, trout (Salmo), which need clean water. Eels (Anguilla), crucian carp (Carasius) and some others also tolerate a considerable degree of pollution. 

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