First records of Rhamdella longiuscula from Argentina and new localities for Rhamdella cainguae ( Siluriformes : Heptapteridae )

The genus Rhamdella is considered to be composed of six species but only R. aymarae and R. cainguae have been recorded from Argentina. Information on the distributions of these species is scarce and R. cainguae is only known from its type locality. This note documents a wider distribution range of R. cainguae and reports R. longiuscula in Argentina for the first time.

The genus Rhamdella, established by Eigenmann & Eigenmann, 1888 as a subgenus of Rhamdia (Bleeker, 1858), is currently a genus belonging to the family Heptapteridae that comprises catfishes of small and medium size.About 37 nominal species have been included in the genus since its description, and at least 14 were considered as valid in the checklist of catfishes provided by Ferraris (2007).
Most of the specimens were collected by the authors in different streams of Misiones province in Argentina, using fishing rods and gillnets.The collecting sites are indicated at Figure 1.Specimens were fixed in a 10% formalin solution and conserved in 70% alcohol.Measurements were taken as straight line distances with a digital caliper following those of Lundberg and MacDade (1986).
Identification of specimens was made based on their original descriptions and considered the delimitation of the genus Rhamdella following Bockmann and Miquelarena (2008).Bockmann & Miquelarena, 2008 (Figures 2 and 3).

Rhamdella cainguae
Morphometric data are given in Table 1.This species is distinguished from the other species of the genus by the presence of a large ovoid and well differentiated area in the supraorbital laterosensory canal between the frontal and sphenotic bones (Figure 4).It also differs from R. aymarae and R. longiuscula by the branchiostegal membrane that does not reach the base of pectoral fin spine, eye diameter 20.Lucena & da Silva, 1991 (Figures 6 and 7).

Rhamdella longiuscula
Morphometric data are given in Table 2.This species differs from R. cainguae and R. aymarae, also present in Argentina, by the dorsal profile of the snout convex vs. slightly convex in R. cainguae and almost straight in R. aymarae, larger eye diameter 22.5-29.4%HL vs. 20.6-23.9 and 11.5-17.3respectively, and lesser interorbital distance 12.8-17.7%HL vs. 17.9-20.3and 31.0-44.9respectively.Additionally, R. longiuscula differs from R. aymarae by the interdorsal distance 6.4-11.3 vs. 16.8-23.4%SL and from R. cainguae by the extension of its branquiostegal membrane that reaches the pectoral spine (Figure 8).The specimens considered herein were collected in Shangay and an unnamed stream (Figure 9), Uruguay River basin at Misiones province.Here we report the presence of R. cainguae in streams not connected to Cuña Pirú, but both being part of Paraná basin.Thus, we document the extension of the distribution range of this species 39 km northwest and 71 km southwest suggesting that it is not a very restricted endemism.
Rhamdella longiuscula is distinctly widespread compared with its congeners.In recent years, it was reported from some new localities in República Oriental del Uruguay (Santa Lucia and Negro Rivers and Merín Lake) by Texeira de Mello et al. ( 2011) and Serra et al. (2014), but the records of this species from the Shangay and the unnamed streams constitute the first from Argentina.
It is interesting that, in its original description, Rhamdella longiuscula was considered to inhabit middle Uruguay River basin and this concept was replicated by subsequent authors (Bockmann and Guazzelli in Reis et al. 2003;Ferraris 2007;Texeira de Melo et al. 2011;Serra et al. 2014).We adopt the delimitation proposed by Piálek et al. (2012), which considers Moconá Falls (Saltos del Moconá, Saltos de Yucumã) and Salto Grande Falls (today replaced by the Salto Grande Dam) as the delimitation between the Upper and Middle and the Middle and Lower Uruguay River respectively.So, based on all available data, we consider R. longiuscula as distributed in the whole Uruguay River basin.