A mysterious new fish, commonly known as 'pacu' among Brazilians was found back in 2007 but it was assigned to a wrong genus. The fish is a relative of the piranha and was again collected by sport fishermen from Rio Madeira basin, Brazil and now properly named and described.
Among the distinctive features of the new fish, are its characteristic teeth, specialized to crush seeds. The new species is quite large, growing up to 47,5 cm. It dwells in moderately to rapidly flowing clear rivers, running over rocky or sandy bottoms, and ranging from about 2 to 8 m in depth.
The name of the new fish was actually chosen as a tribute to Mauricio Camargo-Zorro, a researcher at the Instituto Federal de Educacao, Ciencia e Tecnologia, in recognition of his contribution to the fish fauna inventory from the Marmelos Conservation Area. However, zorroi is also a playful reference to the Latin American fictional character Don Diego de la Vega better known as Zorro.
For the experts: Myloplus zorroi sp. n. is described from the Rio Madeira Basin in Amazonia. The new species had been treated as an undescribed Tometes species because of the absence of a marked abdominal keel and few small spines forming its prepelvic serrae, features commonly found in the species of the Myleus clade of the Serrasalmidae (species of genera Myleus, Mylesinus, Ossubtus and Tometes) and also in species of Utiaritichthys. Myloplus zorroi sp. n. shares the following characters with its congeners and Utiaritichthys: molariform teeth (versus incisiform teeth in Myleus clade members); a labial row of premaxillary teeth separated from lingual row by an internal gap (versus absence of internal gap between premaxillary teeth rows); and an ascending process of premaxilla wide from its base to the tip (versus ascending process tapering from its base to the tip). Like other Myloplus species, M. zorroi sp. n. differs from Utiariticthys by having a deeper body, approximately 60% of standard length (versus usually less than 50% of standard length). Considering all the morphological evidence, including the presence of 13–19 low spines forming the prepelvic serrae in M. zorroi sp. n. versus more than 20 high spines forming a marked prepelvic keel in other species of Mylopus, the new species is here assigned to Myloplus. Comparisons of the new species with nominal species of Myloplus, representatives of the Myleus clade, and other related taxa are provided.