Gymnotus cuia n. sp. Figure 7, Table 1 Synonyms: G. aff. carapo —(Bertaco et al. 2016; Cognato et al. 2007a; b; Cognato & Fialho 2006; Malabarba et al. 2013; Serra et al. 2014). Holotype: UFRGS 23700, 193 mm, Brazil, Rio Grande do Sul, Viamão, Lagoa Verde, Itapuã State Park, Rio Grande, do Sul (30°22’52”S, 051°01’25”W). Paratypes: UFRGS 6854 (5), 104–169 mm, same locality as UFRGS 23700; UFRGS 6855 (3), 164–279 mm, same locality as UFRGS 23700; UFRGS 6857 (4), 152–236 mm, same locality as UFRGS 23700; UFRGS 6858 (2), 168–223 mm, same locality as UFRGS 23700; UFRGS 6859, 266 mm, same locality as UFRGS 23700; UFRGS 8655, 130 mm, same locality as UFRGS 23700; UFRGS 9103 (2), 216–237 mm, same locality as UFRGS 23700; UFRGS 9104, 153 mm, same locality as UFRGS 23700; UFRGS 9105 (2), 125–131 mm, same locality as UFRGS 23700; UFRGS 9106 (2), 152–187 mm, same locality as UFRGS 23700; UFRGS 9115, 166 mm, same locality as UFRGS 23700; UFRGS 9790 (4), 188–261 mm, same locality as UFRGS 23700; UFRGS 9794 (4), 171–217 mm, same locality as UFRGS 23700. Non-Types (Type locality was restricted to Lagoa Verde, Viamão, Itapuã State Park, Rio Grande, do Sul, Brazil): Argentina: MLP 110805 (3), 183–221 mm, Corrientes, Río Paraná (~ 27°27’28.41”S, 058°47’54.13”W); UF 125973 (4), 197–238 mm, Formosa, Río Bermejo drainage, ponds near Río Bermejo (~ 26°13’39”S, 058°09’60”W). Brazil, Mato Grosso do Sul: MZUSP 59316, 198 mm, Corumbá, Rio Vermelho drainage. Brazil, Rio Grande do Sul: MCP 19550 (2), 185–270 mm, São Gabriel, bridge over Banhado do Inhatium (30°15’43”S, 054°31’33”W); MCP 19999 (2), 265–305 mm, Sapiranga, Arroio Feitoria (29°34’00”S, 051°00’00”W); MCP 41952 (4), 140–205 mm, Rio Cacequi drainage, stream alongside RS640 to Cacequi (29°55’23”S, 054°49’52”W); MCP 42587, 208 mm, Viamão, Lagoa Negra, Itapuã State Park (30°21’35”S, 050°58’34”W); UFRGS 10066, Porto Alegre (30°07’32.57”S, 051°11’22.21”W); UFRGS 16370, 206 mm, Viamão, Area de Preservação Ambiental Banhado dos Pachecos (30°07’44.63”S, 050°50’17.67”W); UFRGS 5618 (2), 261–264 mm, Viamão, Lagoa Negra, Itapuã State Park (30°21’35”S, 050°58’34”W); UFRGS 5738, 162 mm, Santa Rosa, Lageado do Pessegueiro; UFRGS 6536, 208 mm, same locality as UFRGS 5618; UFRGS 6537, 233 mm, same locality as UFRGS 5618; UFRGS 6538, 195 mm, same locality as UFRGS 5618; UFRGS 6539, 195 mm, same locality as UFRGS 5618; UFRGS 6540, 130 mm, same locality as UFRGS 5618; UFRGS 6541, 140 mm, Sanga do Jacaré, 82 km from Alegrete (30° 12’42”S, 055°03’17”W); UFRGS 6544 (c&s), same locality as UFRGS 6541; UFRGS 6542, 152 mm, same locality as UFRGS 6541; UFRGS 6543, 198 mm, same locality as UFRGS 6541; UFRGS 6548, 241 mm, Terra de Areia, Rio Três Forquilhas (29°33’22”S, 050°04’19”W); UFRGS 6549, 203 mm, same locality as UFRGS 6548; UFRGS 6550, 116 mm, Eldorado do Sul, Arroio Passo dos Carros (30°05’54”S, 051°23’18”W); UFRGS 6551, 115 mm, same locality as UFRGS 6550; UFRGS 6553, 172 mm, Eldorado do Sul, Arroio Passo dos Carros (30°02’55”S, 051°23’34”W); UFRGS 6554, 135 mm, same locality as UFRGS 6553; UFRGS 6555, 128 mm, same locality as UFRGS 6550; UFRGS 6556, 166 mm, São Gabriel, Rio Uruguai drainage, Arroio Piraí (30°18’56”S, 054°24’22”W); UFRGS 6557, 143 mm, same locality as UFRGS 6556; UFRGS 6558, 191 mm, same locality as UFRGS 6556; UFRGS 6559, (c&s), same locality as UFRGS 6556; UFRGS 6560, 145 mm, same locality as UFRGS 6556; UFRGS 6561, 197 mm, same locality as UFRGS 6556; UFRGS 6573, 217 mm, Terra de Areia, streams in the Reserva Biológica da Mata Paludosa (29°30’41”S, 050°06’27”W); UFRGS 6581, Agudo, Arroio Corupá along the road from Agudo to UHE Dona Francisca (29°33’54”S, 053°17’09”W); UFRGS 6587 (2), 159–170 mm, same locality as UFRGS 6581; UFRGS 6589, 268 mm, same locality as UFRGS 6587; UFRGS 8265 (2), 212–245 mm, Charqueadas (29°57’31”S, 051°33’10”W). Brazil, São Paulo: MZUSP 79348, 222 mm, Reservatório de Barra Bonita, Rio Tietê (22° 31’56”S, 048°31’05”W); MZUSP 83409, 195 mm, Bariri, Rio Tietê a near UHE Bariri road; MZUSP 83421 (2), 20–181 mm, Rio Tietê drainage, Bariri, Queixada stream (22°08’00”S, 048°44’33”W); MZUSP 83427 (5), 90.6–146 mm, Rio Tietê drainage, Bariri, Catingueiro stream (22°07’00”S, 048°45’05”W). Paraguay: MNHNP 189, PTE Hayes, General Bruguez, lake on the premises of the General José M. Brugues military base (24°44’33”S, 058°50’10”W); MNHNP 1064, Alto Paraná, Río Aray, dry stream below the dam; MNHNP 1070 (3), PTE Hayes, "La Golondrina" Hotel, small puddle (~24°31’00”S, 058°40”10”W); MNHNP 1620, Cordillera, Piribebuy, Saltos de Pirareta, 500 m below the falls (25°30’24”S, 056°55’32”W); MNHNP 1734 (2); MNHNP 3389 (2), Alto Paraguay, Tajamar, Madrejon, 50 m from the administration building (20°37’34”S, 059°52’47”W). Uruguay: UFRGS 7990 (2), 144– 206 mm, Artigas, Río Uruguay, Arroyo Guaviyú (30°37’51”S, 057°41’18”W). Diagnosis. Gymnotus cuia is most similar to the sympatric G. c. australis, from which it differs on the following characters: 1, a shorter head (HL 9.8%–12.2% TL, mean 10.9% TL, vs. 11.7%–14.0% TL, mean 12.9% TL); 2, a deeper body (BD 85.4%–133.3% HL, mean 110.6% HL vs. 67.0%–98.8% HL, mean 87.9% HL); 3, a deeper head (HD 61.9%–80.2% HL, mean 68.5% HL vs. 51.2%–64.6% HL, mean 59.7% HL) (Figure 8). Gymnotus cuia is also morphologically similar to the sympatric G. omarorum, from which it differs on by the following characters: 1, more anal-fin pterygiophore scales (APS 6–10, mode 8 vs. 5–6, mode 6); 2, more pored lateral-line scales anterior to the first ventral lateral-line ramus (PLR 32–47, mode 37 vs. 23–30, mode 27); 3, fewer ventral lateral-line rami (VLR 14–28, mode 22 vs. 28–30, mode 29). Gymnotus cuia further differs from all other members of the G. carapo clade in possessing a color patter comprised of 21–29 (mode 28) obliquelyoriented, chocolate-colored bands with wavy, irregular margins and pale interbands less than one-third width of dark bands at mid-body vs. bands interrupted into patches anterodorsally, with silver, blue or green metallic countershading on dorsum of adults of G. arapaima, dark bands lost in large adults (> 250 mm) of G. ardilai, small, rounded dark spots over entire body except posterior 20% of some specimens of G. bahianus, bands faint or absent in all specimens of G. chimarrao, one to three inverted Y -shaped dark bands posteriorly and pale bands not reaching above lateral line in anterior two thirds of body of G. choco, bands broken into speckles throughout in G. diamantinensis, narrow pale bands ( 150 mm with distinct margins, specimens 200–300 mm more faintly banded). Head never banded, spotted, or blotched, dark brown grading to lighter brown dorsally to ventrally. Numerous chromophores speckled over branchiostegal membranes and ventral surface of head. Pectoral-fin rays brown, interradial membranes hyaline. Anterior 80% of anal fin membrane dark brown, gray or black, posterior 20% translucent. 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). Electric Organ Discharge: The EOD waveforms of G. cuia were previously described by Crampton et al. (2013) as “ Gymnotus n. sp. ITU”. The head-to-tail EOD waveform sensu Waddell et al. (2016) of G. cuia is tetraphasic with a dominant P1-P2 phase flanked by a lower voltage negative P0 phase and very low and variably present positive P3 phase (Figure 10). A positive P-1 phase preceding P0 is invariably absent. This EOD waveform conforms to the ht-EOD category 2 of Crampton et al. (2013). The (red) waveforms in Figure 10 refer to specimens of G. cuia collected from the Lagoa dos Patos and Rio Uruguai drainages of Rio Grande do Sul, Brazil. The peak power frequency of the EODs for G. cuia depicted in Figure 10 range from 0.832–1.484 kHz, mean 1.029, standard deviation 0.135 kHz (n=23 recorded specimens). We reported resting pulse rates (1 minute averages) for G. cuia in the range 31–52 Hz, mean 44 Hz (n= 15 specimens). In Rio Uruguai drainages of Rio Grande do Sul G. cuia (red EODs in Figure 10, UFRGS 6556-6561) occurs in sympatry and syntopy with G. carapo australis (black EODs in Figure 10, UFRGS 6763). This species was reported in Crampton et al. (2013), Figure 2, as “ G. sylvius ”. The pentaphasic EOD waveform of G. carapo australis conforms to the ht-EOD category “3” of Crampton et al. (2013) and is readily distinguishable by the invariable presence of both a P-1 and P3 phase. The EOD of G. carapo australis is also shorter, throughout all phases, than that of G. cuia, with a consequent higher peak power frequency, which ranges from 1.289–1.676 kHz, mean 1.476, standard deviation 0.19 (n=3 recorded specimens). We reported resting pulse rates (1 minute averages) for G. carapo australis in the range 46–51 Hz, mean 49 Hz, n = 3 specimens).

Published as part of Craig, Jack M., Malabarba, Luiz R., Crampton, William G. R. & Albert, James S., 2018, Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics, pp. 47-73 in Zootaxa 4379 (1) on pages 55-59, DOI: 10.11646/zootaxa.4379.1.3, http://zenodo.org/record/1172318