A natural hybrid of Leuciscus cephalus and Alburnus alburnus (Pisces, Cyprinidae) from the Ibar River, Western Serbia

The hybrid Leuciscus cephalus × Alburnus alburnus was recognized in studying structure of the ichthyofauna of the middle course of the Ibar River, a right-hand tributary of the Western Morava (system of the Danube on the territory of Serbia). It is a hybrid reciprocal to the natural hybrid Alburnus alburnus × Leuciscus cephalus from the same river system (the Gruža River, a left-hand tributary of the Western Morava), which was described previously by the present author. The hybrid was identified on the basis of its intermediate characteristics and characteristics of the parent species such as pharyngeal bones and teeth; shape of the scales; number, form, and structure of radial canals of the scales; morphology of branchiospinae on the first gill arch; and a complex of meristic and morphometric characters. With respect to its characteristics, this hybrid, like the hybrid Alburnus alburnus × Leuciscus cephalus, is closer to L. cephalus. However, in general appearance the hybrid more closely resembles the presumed maternal species. The phenomenon of reciprocal hybridization is discussed at some length