Abstract
A new species of Characidium is described from a small, isolated river in the highland areas of Noel Kempff Mercado National Park, Bolivia. The new taxon can be diagnosed by the presence of a relatively broad and conspicuous dark midlateral stripe extending from the tip of snout to the base of the caudal fin, markedly darker than the vertical bars (when present), added to the absence of a distinct humeral blotch. Additional distinguishing features include a complete lateral line, presence of adipose fin, 12 circumpeduncular scale rows, four horizontal scale rows above the lateral line, presence of the parietal branch of the supraorbital canal and a conspicuous basicaudal spot. Some specimens also exhibit reddish‐brown pigmentation on the paired, dorsal and caudal fins, a condition otherwise restricted to few congeners. This discovery highlights the hidden fish diversity of poorly explored highland rivers and protected areas within Neotropical region. In addition, we discuss osteological features of the Weberian apparatus, documented for the first time in the genus using computed tomography (CT) scan imagery. Also, geomorphological processes that may have influenced the isolation of the new species on the Huanchaca Meseta are discussed.