A new species of Chondrostoma Agassiz, 1832 (Cypriniformes: Cyprinidae) with sexual dimorphism from the lower Rio Tejo Basin, Portugal

Abstract

Chondrostoma olisiponensis sp. nov. is described from the lower Rio Tejo Basin. It is a small species (all specimens examined less than 105mm SL) distinguished from the other species of Chondrostoma s.l. by the following combination of characters. Chondrostoma olisiponensis lacks a horny blade on the lower jaw, has a pronouncedly arched mouth, and lacks an intense reddish coloration at the base of the fins. It has elongated pelvic fins that reach the anus and often pass the anal-fin insertion in males, and dorsal, pelvic and anal fins usually have 8 branched rays. The new species has 36 to 43 scales in the lateral line, 7.0 to 8.5 scales above the lateral line, 13 to 16 circumpeduncular scales, denticulated (vs. smooth) grinding teeth surfaces, 6-5/5 pharyngeal teeth and 15 to 19 gill rakers. Chondrostoma olisiponensis is further distinguished from C. lusitanicum, a phylogenetically close species that lives in the same area, by having a higher body, a relatively longer head, and a larger eye. The origins of anal and pelvic fins are displaced anteriorly, while the origin of pectoral fins is displaced posteriorly. Pelvic and pectoral fins and last anal-fin ray are longer in the new species. Unlike the other species in the genus, C. olisiponensis shows external sexual dimorphism, with males having longer pelvic fins whose extremities pass the anus and often overlap with the anal fin. This description raises concerns on the recently proposed splitting of Chondrostoma s.l. since the morphological traits deemed characteristic of some genera are unsuitable for their diagnosis. The species should be considered Critically Endangered (CR) according to IUCN criteria B1ab(ii,iii,iv)c(iv)+2ab(ii,iii,iv)c(iv).