Tuesday, October 25, 2016

[Ichthyology • 2016] Pseudacanthicus pirarara • A New Species of the Leopard Pleco Genus Pseudacanthicus (Siluriformes: Loricariidae) from the Rio Xingu, Brazil

Pseudacanthicus pirarara 
  Chamon & Sousa, 2016  

 DOI: 10.1111/jfb.13184  


The genus Pseudacanthicus comprises six valid species distributed in the Amazon basin and Caribbean coastal drainages from Guyana to French Guiana: P. serratusP. fordiiP. histrixP. spinosusP. leopardus and P. pitangaA new species of Pseudacanthicus is described from the Rio Xingu Basin, distinguished from its congeners by the following combination of characters: presence of anastomose dark blotches forming continuous zigzag bands alongside longitudinal keels; presence of dark blotches on ventral surface of body and head; all fins with orange to red colour on unbranched rays and sometimes subsequent branched rays. Brief comments on ornamental fisheries and conservation of the new species are also provided.

Keywords: Amazon Basin; conservation; fish trade; Neotropical; taxonomy

Figure 2.  Pseudacanthicus pirarara, live specimens showing variation in colour:
(a) Laboratório de Ictiologia de Altamira, Universidade Federal do Pará, Campus de Altamira—LIA 1466, 58·0 mm standard length (LS), Rio Xingu near São Félix do Xingu; (b) ANSP 197879, 137 mm LS, Rio Irini; (c) LIA 1251, 122·5 mm LS, Rio Xingu near São Félix do Xingu; (d) Academy of Natural Science of Philadelphia—ANSP 193003, 193 mm LS, Rio Irini; (e) LIA 1297, 141·0 mm LS, Rio Xingu near São Félix do Xingu; (f) LIA (no number), 173·75 mm LS, Rio Xingu near Altamira. 

Diagnosis: Pseudacanthicus pirarara is distinguished from congeners (except P. leopardus and P. pitanga) by having fins with intensely orange to red colouration (v. fins with dark background colour with white spots in P. serratus and P. fordii or grey background colour with black blotches in P. histrix and P. spinosus). Pseudacanthicus pirarara is distinguished from P. leopardus by the presence of anastomose dark blotches forming continuous zigzag bands alongside longitudinal keels and having all fins with strong red colour on unbranched rays and sometimes in subsequent branched rays (v. dark blotches distinct, never connected and red colour restricted to dorsal and caudal-fin rays). From P. pitanga, P. pirarara is distinguished by the presence of conspicuous dark blotches on head and abdomen (v. dark blotches usually absent or otherwise faint on head and always absent on abdomen). Pseudacanthicus pirarara is further diagnosed from congeners by the following combination of osteological characteristics: nasal bone L-shaped (v. rectangular); ventral crest of basipterygii straight (v. rounded or triangular); internal crest of posterior process of basipterygii well-developed (v. crest absent or weak).

Etymology: The specific name (a noun in apposition) is an allusion to Pirarara, the Brazilian common name of the red tail catfish, Phractocephalus hemioliopterus (Bloch & Schneider 1801), which was incorporated by local fishermen in the common name of the species (i.e. assacu-pirarara) due to its reddish fins. Assacu is a common name for the Amazon tree Hura crepitans (Euphorbiaceae), which has bark covered with conical spines.

Distribution: Pseudacanthicus pirarara is endemic to the Rio Xingu Basin and has been collected in the main channel from Vitória do Xingu to São Félix do Xingu and major tributaries to the Xingu like Rio Bacajá and Rio Iriri (Fig. 3).

Figure 4. Typical habitat where Pseudacanthicus pirarara occurs:
(a) stretch of the Rio Xingu at Gorgulho da Rita region, a shallow, fast-flowing portion of the river with gravel and conglomerate rocks on the bottom; (b) and (c) Pseudacanthicus pirarara in natural habitat at Gorgulho da Rita. 

Ecological notes: The species can be found in the main channel of the river, in moderate to strong currents and shallow to deep environments down to 15 m. It is usually collected at depths of 2–3 m, often hiding beneath bedrock or conglomerate plates of rocks and gravel (Figs 4 and 5). Pseudacanthicus pirarara is not a gregarious species and it is not usually found with conspecific individuals or other species. They are carnivorous and feed on small invertebrates. According to local fishermen, they are more easily found during the high-water season (December to April), probably due to reproductive behaviour.

Fisheries and economical importance: Pseudacanthicus pirarara is highly appreciated by advanced hobbyists in the international aquarium trade because it is a large and colourful species that requires special tank set-ups to best suit their needs. It is also an important resource for local fishermen in the Rio Xingu, being one of the more valuable species depending on season. Local fishermen refer to it as assacu-vermelhoassacu-pirarara or L025 (Schraml & Schäfer, 2004; Stawikowski et al., 2004; Werner et al., 2005). It is usually captured with the aid of an air compressor and hoses that supply breathable air to the fishermen during 20–30 min dives. The safety procedures for such dives, however, are far from satisfactory.

Chamon, C.C. and Sousa, L.M. 2016. 2016. A New Species of the Leopard Pleco Genus Pseudacanthicus (Siluriformes: Loricariidae) from the Rio Xingu, Brazil.  Journal of Fish Biology.  DOI: 10.1111/jfb.13184