Yliki Roach

Leucos ylikiensis has 12 soft rays supporting the dorsal fin and 11 supporting the anal fin. One feature which distinguishes the Achelous roach from other species in the genus Leucos is its moderate size, almost never exceeding 12 or 13 cm (4.7 or 5.1 in), standard length. It is also separable by the lack of a dark midlateral band, the peritoneal membrane being covered in a dense pattern of black melanophores, and the lateral line having 42 or 43 pored scales. However, the number of gill rakers is the most notable feature, with this species having a total of 18 to 20, compared to 8 to 16 in other white roaches. The maximum published fork length for this species is 28.5 cm (11.2 in).

Leucos ylikiensis is endemic to Boeotia in Central Greece, where it is found in the Cephissus River and in lakes Yliki and Paralimni, with an introduced population in Lake Marathon reservoir north of Athens. This species is regarded as a relict of the fauna of the large Lake Copais, which was drained in the late 19th century. This species is found in the pelagic zone of the lakes it occurs in.

Leucos ylikiensis belongs to the genus Leucos. This name is derived from the Greek leukos, which means "white". The genus was named by Johann Jakob Heckel. He did not explain why he chose this name, but it may refer to the silvery colour of Squalius aula. The specific name, ylikiensis, means "belonging to Yliki", i.e Lake Yliki, part of the type locality.