The rio Madeira is the largest white-water tributary of the Amazon, and is currently the river drainage with the highest fish species diversity in the world. A new species of Panaqolus was recognized from the middle Madeira and Mamoré rivers (Brazil) and from the Madre de Dios drainage (Peru) and it is described herein. This new species is readily distinguished from its congeners by the large number of white dots distributed all over the body and by its remarkable amplitude of color pattern variation, ranging from a pale, light brown, to dark brown and almost black background coloration. The new species closely resembles P. albomaculatus but has more and smaller dots on the body, a smaller orbital diameter (12.5-16.8% head length vs. 16.0-20.0%) and longer maxillary barbels (9.7-19.6% head length vs. 1.6-8.9%). The new species is the second of the genus Panaqolus described for a Brazilian location after nearly 80 years of the description of P. purusiensis.
Key words: Amazon; Catfish; Key of Identification; Panaque; Peckoltia
Distribution and Habitat. The known distribution of this species is the Madeira basin, including the Madeira, Mamoré, and Tambopata (Madre de Dios drainage) rivers (Fig. 6). Most of the specimens have been collected in cofferdams at the construction sites of the hydroelectric power plants of Santo Antônio and Jirau (former Santo Antônio and Jirau rapids), on the rio Madeira, by several technicians and ichthyologists hired by the two Consulting Environmental Companies responsible for the biological inventories in the area. Most of the remaining specimens have been caught in depths of 3.1 to 11 m (UFRO-I 6384, INPA 39605, MZUSP 114009) and 4.1 to 8.5 m (UFRO-I 6384) using trawl nets. This indicates that this species prefers deep-water habitats with strong current, which might help to explain its relative rarity in scientific collections.
Etymology. From the Latin nix meaning snow, alluding to the color: in dark individuals the dots look like falling snowflakes, while pale individuals look like they have the whole body covered by snow; treated as a noun in apposition.
Panaqolus nix shows a remarkable plasticity in coloration: the base coloration can be uniformly yellowish-white, pale brown, or dark brown to nearly black. Specimens that showed a light coloration when collected, changed to a nearly black coloration when in an aquarium. Panaqolus nix showed a color pattern very different from most of its congeners that present a color pattern with bands or saddles. The other Panaqolus species with uniform coloration are P. nocturnus, from Peru, Río Marañon basin, and large P. purusiensis, from upper rio Purus. Panaqolus nix is the first species of the genus reported to be caught using trawl nets and also the first that seems to have a preference for deeper habitats. Besides, P. nix is the species in the genus with the smallest eyes what might be related to its capacity to explore deeper benthonic habitats. The other Panaqolus species with small orbits is P. purusiensis. However, P. nix has a more elongate body and shallower caudal peduncle depth, whereas P. purusiensis present a more robust and truncate body form. Schaefer & Stewart (1993) called attention for the reduced number of vertebrae in the holotype of P. purusiensis (26 vs. 28 in all other species of Panaqolus) and that the holotype showed some sort of teratology. However, the authors also remark that morphometric proportions related to caudal peduncle length did not differ between the holotype and the topotype. Young and subadult P. purusiensis are also reported as presenting bands on body and fins, differently from P. nix. Panaqolus nocturnus is also close to P. nix but it differs from the latter by the larger orbit and completely lack of clear dots along body and fins.
Coloration, presence of caudal-fin filaments and the angle between the dentary tooth rows suggest that P. nix is closely related with P. albomaculatus and P. albivermis. However, P. albomaculatus has a larger orbit, fewer teeth and shorter barbels than P. nix, whereas P. albivermis shows a quite conspicuous and peculiar color pattern with thin light transversal lines on body and fins. In the aquarium hobby, P. nix has been introduced as Panaqolus sp. L395, having been found in the Madre de Dios basin in Peru (Evers, 2005).
O rio Madeira é o maior afluente de água branca do rio Amazonas e é atualmente o rio com o maior número de espécies do mundo. Uma nova espécie de Panaqolus foi reconhecida do médio rio Madeira, do rio Mamoré (ambos no Brasil) e da bacia do Río Madre de Dios (Peru) e é descrita aqui. Esta nova espécie se distingue de suas congêneres pela grande quantidade de pontos brancos espalhados pelo corpo e grande variabilidade na sua coloração, variando de um fundo branco a marrom claro até marrom escuro e quase preto. A espécie se assemelha a P. albomaculatus da qual se distingue por ter mais manchas de menor tamanho no corpo, olhos menores (12,5-16,8% do comprimento da cabeça vs. 16,0-20,0%) e barbilhões maxilares mais compridos (9,7-19,6% comprimento da cabeça vs. 1,6-8,9%). A nova espécie é a segunda de Panaqolus descrita para uma localidade no Brasil, aproximadamente 80 anos após a descrição de P. purusiensis.
Cramer, C.A. & Rapp Py-Daniel, L.H. 2015. A New Species of Panaqolus (Siluriformes: Loricariidae) from the rio Madeira Basin with Remarkable Intraspecific Color Variation. Neotropical Ichthyology, in press. DOI: 10.1590/1982-0224-20140099