A study of the South American giant trahiras has shown that one member of the Hoplias genus has been described twice under different scientific names.
A study of two trahira species from French Guiana by a team of Brazilian ichthyologists has shown that Hoplias macrophthalmus was described in 1907, despite the same species being described by Valenciennes from the same locality in Cayenne 61-years previously.
George Mattox, Monica Toledo-Piza and Osvaldo Oyakawa studied 200 specimens of Hoplias macrophthalmus and Hoplias aimara measuring between 3cm/2" and 62cm/25" and analysed their meristic and morphometric features to determine whether they were distinct and to see whether they could detect any geographic differences in the fish. Their findings are published in the latest edition of the ichthyological journal Copeia.
The results showed that both Hoplias aimara and Hoplias macrophthalmus were largely identical. Since the same species had been described by Pellegrin in 1907 under a new name - macrophthalmus - it must be renamed, with the oldest name, H. aimara, taking precedence under the Principle of Priority rules of the International Code of Zoological Nomenclature.
The authors said: "This species is distinguished from congeners by the presence of a vertically-elongate dark spot on the median portion of the opercular membrane and by the absence of the accessory ectopterygoid. Hoplias aimara occurs in the drainages of Rio Tocantins, Rio Xingu, Rio Tapajs, Rio Jar, and Rio Trombetas, in coastal drainages of the Guyanas, Suriname, and state of Amap, Brazil.
"In the Ro Orinoco basin, the species occurs only in the Ro Caron and rivers to the east of this drainage. Literature records of Hoplias aimara for the Rio Purus and upper Ro Orinoco were based on misidentifications."
Hoplias are members of the Erythrinidae family of Characiformes and are related to the similarly toothy Hoplerythrinus and Erythrinus. Recent research on the related Hoplias malabaricus published in August showed for the first time the reproductive behaviour of Hoplias.
The Hoplias genus now includes around eight valid species, including: H. aimara; H. brasiliensis; H. lacerdae; H. malabaricus; H. microcephalus; H. microlepis; H. patana and H. teres.
For more details on the changes see the paper: Mattox GMT, Toledo-Piza M and OT Oyakawa (2006) - Taxonomic Study of Hoplias Aimara (Valenciennes, 1846) and Hoplias macrophthalmus (Pellegrin, 1907) (Ostariophysi, Characiformes, Erythrinidae). Copeia: Vol. 2006, No. 3, pp. 516-528.