Barbus sensitivus, a new species with extensive pitlines from the Sanaga River (Teleostei: Cyprinidae)

Tyson R. Roberts

aqua, International Journal of Ichthyology, pp. 187-196, Volume 16, Issue 4 – 15 October 2010


Barbus sensitivus new species, from the Sanaga River in Cameroon, West Africa, has a much more slender caudal peduncle than any other small African barb. It also has extensively distributed exposed pitline organelles in pit lines on the head and scales, illustrated here by scanning electron micrographs. Similar pit lines and pitline organelles evidently occur in various other Old World barbs assigned to various genera in Africa and Asia but adequate comparative studies including SEM observations are not available to permit their comparison and identification. None of the species previously described are very similar to this new species. The pitline organelles of B. sensitivus n. sp. have exposed or free neuromasts. Their sensory modality presumably is mechanosensory. Extensively distributed in large pit lines on the head and body of adult B. sensitivus n. sp., they are similar to lateral line neuromast organs in advanced larvae of Cyprinus carpio, Gnathopogon elongatus caerulescens, and Danio rerio. They are most concentrated on the ventrolateral part of the head, which has about 3000 of them, most bearing 20 to 100 kinocilia up to 7 micra long and 0.4 micra in diameter. Pit lines with smaller pitline organelles and fewer kinocilia occur in rows on the scales of the body and on the dorsal surface of the head but are absent from the fins. Their presence in adult B. sensitivus new species might represent a neotenic retention. In larval Gnathopogon elongatus caerulescens they facilitate detection of tiny planktonic prey such as Artemia when feeding under reduced light conditions.

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