Threatened fishes of the world: Ossubtus xinguense (Jégu 1992) (Characidae: Serrasalminae)

Abstract

Common names: eaglebeak pacu (US), Adlerschnabel-pacu (GER), pacu-capivara, pacu-tromba-de-anta (BRA). Conservation status: Endangered. Identification: D 21-23, A 23-26, vertebrae 38. The body is ovoid. The profile of the snout is blunt. Among the serrasalmins this species is characterized by a series of synapomorphies linked to its uncommon rotation of the head plan during the early stages of life. The mouth is terminal in postlarval stage, slightly downturned in specimens of around 30 mm SL and strictly ventral in specimens larger than 50 mm SL. The lower edge of the eye is located very dorsally of the commissure of the mouth. The premaxillary has five teeth in the labial series and two in the lingual series. The two median teeth of the labial series are reduced to very short canines. The lower jaw has four incisiform teeth on a single series. The pectoral fins are placed in a very low position on the sides. There are 19-21 branched rays on the dorsal fin and 22-25 on the anal fin. The number of scales in the lateral line varies from 81 to 88 to the hypural. There are 36-42 series of circumpeduncular scales. There are 11-16 postpelvic serrae of which 5-9 pairs of spines are found around the cloaca, but there are no prepelvic serrae. The number of branchiospines varies from 9-10 on the upper branch of the first branchial arch and from 11 to 16 on the lower branch. Maximum SL about 176 mm. Distribution: The presence of Ossubtus xinguense is confirmed in Xingu basin (Para´, Brazil) but restricted to the rapids area around Altamira city. Abundance: Unknown, but apparently rare. Habitat and ecology: Ossubtus xinguense is a strictly rheophilic species. Young specimens of up to 40 mm SL could be observed in schools of 20-30 individuals, sheltered under broad stones in the rapids near Altamira. Large specimens can be captured by castnet in the rapids.

Tometes camunani (Characiformes: Serrasalmidae), a new species of phytophagous fish from the Guiana Shield, rio Trombetas basin, Brazil

“…Tometes, Myleus, Mylesinus Valenciennes, 1850, andOssubtus Jégu, 1992, comprise a monophyletic assemblage based on morphological data (Jégu, 2004). Considering the same taxa, except the monotypic Ossubtus xinguense, Ortí et al (2008) confirmed those previous results using molecular data, and also proposed the term Myleus group.…”

“…All genera of the Myleus group occur exclusively in shield drainages, and are rheophilic and phytophagous, feeding mainly on Podostemaceae (Jégu, 2004). Tometes camunani occurs in association with swift-flowing rapids and rocky outcrops in clear water rivers of the upper rio Trombetas.…”

Length-weight relationships and condition factor of the eaglebeak pacu Ossubtus xinguense Jégu, 1992 (Characiformes, Serrasalmidae), an endangered species from Rio Xingu rapids, northern Brazil

“…After more than two decades of formal description of the O. xinguense little known about it. Jégu and Zuanon (2005) believe the species to be rare, but in this study performed in just three months a considerable number of individuals (N = 149) of the species were captured in the Volta Grande region. However, this region is doomed to have a drastically changed landscape after the conclusion of the construction of Belo Monte hydroelectric dam.…”

“…Ossubtus xinguense, known as 'eaglebeak pacu' in the ornamental fish trade or as 'pacu-capivara' by local communities, is one of the rheophilic, endemic and rare fish from Rio Xingu. Due to its distribution restricted to rapids downstream of Altamira city, this species is seriously threatened by construction of the Belo Monte hydroelectric dam (Jégu and Zuanon, 2005).…”

A new Silver Dollar species of Metynnis Cope, 1878 (Characiformes: Serrasalmidae) from Northwestern Brazil and Southern Venezuela

“…In spite of these taxonomic uncertainties, the monophyly of the genus is well accepted and has been corroborated by various authors in both morphological (Machado-Allison, 1982, 1983Jégu, 2004) and molecular phylogenetic analyses (Ortí et al, 1996(Ortí et al, , 2008Calcagnotto et al, 2005;Thompson et al, 2014), with the exception of Cione et al (2009), which recovered a paraphyletic Metynnis. Species of Metynnis can be easily recognized within Serrasalmidae by having a long adipose-fin base, generally exceeding the distance between the dorsal-fin insertion and adipose-fin origin (Cope, 1878;Eigenmann, 1915;Jégu, 2003).…”