What is "squalius"

Squalius is a ray-finned fish genus in the family Cyprinidae, containing the European chubs (the "European chub" proper is S. cephalus). This genus belongs to the subfamily Leuciscinae as other chubs and daces generally do.

The Eurasian daces, Leuciscus, are close relatives. The present genus was formerly entirely included there, and their delimitation with respect to each other is somewhat uncertain. A number of species have in recent times been moved from one genus to the other. Generally, Leuciscus in the modern sense is widespread across Eurasia, whereas Squalius is almost limited to Europe proper.

Hybridization is not rare in the Cyprinidae, including this genus. S. alburnoides is known to be of ancient hybrid origin, with the paternal lineage deriving from a prehistoric species related to Anaecypris; the latter mated with ancestral S. pyrenaicus. Present-day S. alburnoides mates with sympatric congeners of other species.