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A Natural Hybrid of Leuciscus leuciscus (L.) and Alburnus alburnus (L.) (Osteichthyes: Cyprinidae) from the Bystrzyca River (Poland)

Abstract. 
 A hybrid Leuciscus leuciscus × Alburnus alburnus was found during the ichthyofaunistic studies in the Bystrzyca River, a left-bank tributary of the Odra River (SW Poland). The hybrid was identified on the basis of its intermediate features and characteristics of the parent species (biometrical, osteological and anatomical) such as opercular and dental bones, pharyngeal bones and teeth, shape of scales, number, form and structure of radial canals of the scales, and air bladder and a complex of meristic and morphometric characters. With respect to its characteristics, the hybrid is closer to dace than to bleak. The small abundance of the hybrid shows that the hybridisation was rather accidental.