A scientist has described five new species of toothy characin from the South American genus Acestrocephalus.
Naercio Menezes of the Museu de Zoologia at the Universidade de Sao Paulo in Brazil named the new species Acestrocephalus maculosus, A. stigmatus, A. nigrifasciatus, A. acutus and A. pallidus in a paper in the latest volume of the journal Neotropical Ichthyology.
Until recently, the Acestrocephalus genus held four species - A. anomalus, A. sardina, A. boehlkei and A. ginesi - but new studies of the fish fauna of Brazil revealed a number of new species from the genus.
Acestrocephalus maculosus is a relatively small species and measures around 8cm/3" in length. It is silvery in colour with a dark longitudinal stripe and a dark blotch in the humeral region. It was discovered in a tributary of the Rio do Peixe in Goias, Brazil.
Acestrocephalus stigmatus was discovered in the Rio Araguaia basin in Mato Grosso, Brazil, and measures 8-9cm in length. Like maculosus and boehlkei, it has a dark humeral blotch, but has fewer anal fin rays (29-31) than boehlkei (34-36) and more than maculosus (25-27).
Acestrocephalus nigrifasciatus gets its name from its distinctive longitudinal black stripe, which extends from the humeral region to the caudal peduncle, giving the species a similar appearance to A. sardina. The new species has more scale rows above the lateral line, with 13-14, compared to 10-12 seen in sardina.
A. nigrifasciatus is also from the Mato Grosso, where it is known from the Rio Tapajos, Rio Arinos and Rio Juruena.
Acestrocephalus acutus was discovered by the famous Amazon explorer Michael Goulding, and reaches a size of up to 10cm or so. It was discovered in 1983 in a stream called igarape do Cinzento on the Rio Itacaiunas in Para state.
This species lack a humeral blotch, but has a distinctive black spot on the base of the caudal peduncle.
Acestrocephalus pallidus was discovered in 1975 in the Rio Madeira, ilha do Puruzinho, by Expedio Permanente da Amaznia. Most of the type specimens are small fish, at around 4-6cm.
The authors said: "Acestrocephalus pallidus is distinguished from A. boehlkei, A. maculosus and A. stigmatus by lacking the dark humeral blotch characteristic of these species. Acestrocephalus pallidus has the eye smaller than A. sardina and A. nigrifasciatus and fewer maxillary teeth (30-38 vs 40-46)."
Menezes also redescribes Acestrocephalus sardina and A. boehlkei in the paper.
For more information see the paper: Menezes NA (2006) - Description of five new species of Acestrocephalus Eigenmann and redescription of A. sardina and A. boehlkei (Characiformes: Characidae). Neotropical Ichthyology, 4(4):385-400, 2006.