Achondrostoma oligolepis

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Achondrostoma oligolepis, commonly known as the ruivaco, is a freshwater fish in the dace family Leuciscidae. It is found only in Portugal and prefers slow-moving rivers and streams with aquatic plants and a sandy or gravelly bottom. The ruivaco is currently listed as Least Concern by the IUCN.

Taxonomy and naming: This species is part of the genus Achondrostoma. The genus was created in 2007 after genetic studies split three species from Chondrostoma. The fish was first described in 1866 as Leuciscus macrolepidotus, but that name was invalid because it had already been used for another species. In 2005 scientists gave it the name Chondrostoma oligolepis, and it is now classified in Achondrostoma. The name means “mouth without horny plates” (Achondrostoma) and “few scales” (oligolepis).

Identification: It grows up to about 25 cm, though 15 cm is more typical. It has 30–38 scales along the lateral line, 3–4 scale rows between the lateral line and the pelvic fins, and 11–12 scale rows around the caudal peduncle. The eye is smaller than the snout, the snout is rounded, and the lower jaw joint forms a noticeable angle.

Distribution: The ruivaco is endemic to Portugal, occurring from the Âncora River system south to the Arnoia and Real rivers, which drain into the Óbidos coastal lagoon north of Lisbon.

Habitat: It is a habitat generalist, living in slow rivers and streams with vegetation and sandy or gravel substrates.