Brazilian scientists have described a new species of Moenkhausia tetra from the Amazon and Orinoco river drainages in a recent issue of the journal Zootaxa.
Manoela Marinho and Francisco Langeani name the new tetra Moenkhausia mikai after the common name used by the Tuyuka people (who live in the region of the type locality) for this (and closely similar) species.
Moenkhausia mikai is a member of the M. lepidura group, and can be distinguished from congeners by the combination of a conspicuous, small and circular humeral spot, a black spot on the upper caudal-fin lobe, lower caudal-fin lobe without a spot (or with a faint spot), and the middle caudal-fin rays hyaline or with dark tips.
Mature males also have a unique combination of two large-sized bony hooks on the anal-fin rays and tiny spines on the distal portion of all fins, which immediately distinguishes it from all other tetras in the family Characidae.
For more information, see the paper: Marinho, MMF and F Langeani (2010) A new species of Moenkhausia from the rio Amazonas and rio Orinoco basins (Characiformes: Characidae). Zootaxa 2577, pp. 57–68.