Wednesday, February 14, 2018

[Ichthyology • 2018] Gymnotus cuia • Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics

Gymnotus cuia
Craig, Malabarba, Crampton & Albert, 2018


Banded Knifefishes (Gymnotus, Gymnotidae) comprise the most species-rich, ecologically tolerant (eurytopic), and geographically widespread genus of Neotropical electric fishes (Gymnotiformes), with 40 valid species occupying most habitats and regions throughout the humid Neotropics. Despite substantial alpha-taxonomic work in recent years, parts of the genus remain characterized by taxonomic confusion. Here we describe and delimit species of the G. carapo and G. tigre clades from the southern Neotropics, using body proportions (caliper-based morphometrics), fin-ray, scale and laterosensory-pore counts (meristics), quantitative shape differences (geometric morphometrics), osteology, color patterns and electric organ discharges. We report these data from 174 Gymnotus specimens collected from 100 localities throughout the southern Neotropics, and delimit species boundaries in a multivariate statistical framework. We find six species of the G. carapo clade (G. carapo australisGymnotus cuia n. sp., G. chimarrao, G. omarorum, G. pantanal, and G. sylvius), and two species of the G. tigre clade (G. inaequilabiatus and G. paraguensis) in the southern Neotropics. The new species G. cuia is readily distinguished from the morphologically similar and broadly sympatric G. c. australis by a shorter head and deeper head and body, and from the morphologically similar and sympatric G. omarorum by fewer lateral-line ventral rami and fewer pored lateral-line scales anterior to the first ventral ramus. We also review the geographic distributions of all eight species of the G. carapo and G. tigre clades in the southern Neotropics, showing that G. cuia is the most widespread species in the region. These results affirm the importance of understanding the structure of variation within and between species, both geographic and ontogenetic, in delimiting species boundaries.

Keywords:  Pisces, Alpha taxonomy, Biodiversity assessment, Neotropical, Species delimitation

FIGURE 7. Variation within the type series of Gymnotus cuia.
A. The holotype, UFRGS 23700 (193 mm). B. Four specimens of the paratype series, UFRGS 9794 (171-217 mm).

Gymnotus cuia n. sp.

 G. aff. carapo — (Bertaco et al. 2016; Cognato et al. 2007a; b;
Cognato & Fialho 2006; Malabarba et al. 2013; Serra et al. 2014).

Etymology: The specific epithet is derived from the species’ especially deep body and head, evoking the short, rounded cuia gourd used to drink the traditional mate popular throughout its range. The convention of honoring this practice in gymnotiform taxonomy is shared with G. chimarrao (chimarrão =the mate itself) and Brachyhypopomus bombilla (bombilla = the metal straw used for drinking mate). The common name “ bombilla ” is often used to describe gymnotiform fish throughout the southern Neotropics as well.

Ecology: Gymnotus cuia inhabits lakes and small streams, associated to densely vegetated areas. The species is abundant in the type locality (Figure 9), a shallow lake (less than 1 m deep) with dense emergent vegetation, including Ludwigia peploides (Onagraceae), Utricularia spp. (Lenticulariaceae), Nymphoides indica (Menyanthaceae), Pontederia lanceolata (Pontederiaceae), Azolla sp. (Azollaceae), Eleocharis sp. (Cyperaceae), Cabomba australis (Cabombaceae), Echinodorus sp. (Alismataceae), Lemna valdiviana (Lemnaceae), Scirpus sp. (Sciperaceae) and abundant grass in the shores (Cognato & Fialho 2006). Throughout its distribution it is usually abundant in the roots of dense beds of floating water hyacinths (Eichornia crassipes). Reproductive cycle extends from November to March (Cognato & Fialho 2006).

FIGURE 9. Habitat and live appearance of Gymnotus cuia.
 A. The type locality of G. cuia, Lagoa Verde, Itapuã State Park, Viamão, Rio Grande, do Sul, Brazil. Photo: Diego Cognato. B. Close-up photo of the head of a live G. cuia. Photo: Will Crampton. C. Fullbody photo of of a live G. cuia. Photo: Will Crampton.

Jack M. Craig, Luiz R. Malabarba, William G. R. Crampton and James S. Albert. 2018. Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics.  Zootaxa. 4379(1); 47–73.    DOI: 10.11646/zootaxa.4379.1.3