A natural hybrid of Leuciscus cephalus macedonicus X Chalcalburnus chalcoides macedonicus (Pisces, Cyprinidae) from Lake Volvi (Macedonia, Greece)

A massive hybridization between Leuciscus cephalus macedonicus and Chalcalburnus chalcoides macedonicus has been recognized and studied by examining 67 specimens from Lake Volvi (Macedonia, Greece). The majority of meristic and other characters present an intermediate position in the hybrid (total hybrid index Vh = 38.37). Nevertheless, the best expression of intermediacy is shown most clearly by the numbers of anal fin soft rays, lateral line scales and gill rakers, and also by the height of the dorsal fin and the length of the base of anal fin. Of the examined hybrid specimens. 92.5% were females. It seems that hybridization takes place during the reproduction period in the main streams flowing into the lake under special conditions which hinder the migration of the majority of the population of C. chalcoides from the lake to the breeding sites. It is suggested that individuals of C. chalcoides , which manage to arrive in these sites, mate with L. cephalus , the normal inhabitant of the streams, thus producing the hybrid.