Gymnotus cuia, Craig & Malabarba & Crampton & Albert, 2018

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, Zootaxa 4379 (1), pp. 47-73 : 55-59

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 (<20% width of dark bands) with sharp margins, and pale bands extending fully to dorsal mid-line in G. mamiraua , bands faint or absent from 80% of dorsum in all specimens, and narrow pale bands (<20% width of dark bands) which never extend above lateral line on anterior half of body in G. pantanal , pale bands wider than dark bands in G. sylvius , narrow pale interbands (<33% width of dark bands) extending above lateral line and often to dorsal midline in G. ucamara . Gymnotus cuia further differs from all members of the G. varzea clade ( G. chaviro , G. curupira G. mamiraua , G. obscurus , and G. varzea ) the following characters: 1, relatively more arrowhead-shaped dentary teeth (6 vs. 2–4 in the G. varzea clade except in G. chaviro , G. curupira and G. mamiraua , , with 4–7); 2, anterior 80% of anal fin membrane pigmented, posterior 20% translucent (vs. wholly clear or evenly pigmented in the G. varzea clade); 3, large adult total length (305 mm TL vs. 215 mm – 275 mm TL in the G. varzea clade).

Description: Morphometric and meristic data in Table 1. Sexually monomorphic, including in breeding condition. Total length to 305 mm. Morphological maturity at roughly 110 mm. Scales rounded to slightly ovoid, present on entire postcranial portion of body. Gape large in mature specimens, to or beyond posterior nares. Mouth superior with lower jaw longer than upper, rictus decurved. Chin fleshy and protuberant with fleshy pad of electrosensitive organs overlying tip of snout and oral jaws. Anterior narial pore partially to entirely included within gape in narial fold. Anterior nares large, subequal to eye diameter. Circumorbital series ovoid. Ethmoid region broad between anterior nares, with rounded anterior margin. Eye position lateral, lower margin of eye dorsal or horizontal to rictus. Premaxilla with 13–14 (mode 13) teeth disposed in single row along outer margin, arrowhead shaped anteriorly, conical posteriorly. Curved median margin of premaxilla. Maxilla-palatine articulation near anterior tip of endopterygoid. Maxilla vertical, rod-shaped, narrow distally with a straight ventral margin, length equal to roughly width of four–six dentary teeth. Dentary with one row of 26–27 (mode 26) teeth, 6 arrow-head shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abut at midlength. Dentary posteroventral process shorter than posterodorsal, narrow distally. Dentary ventral margin lamella narrow, depth less than posterior process. Opercle dorsal margin straight to slightly convex. Dorsal opercular process lamellar or rugose, crest absent or small, posterior margin entirely smooth, without spines or processes. Preopercle with anteroventral notch, posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entire, median shelf large, more than one-half width of symplectic. Metapterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base shorter than length, curved, tip simple. Interopercle dorsal margin ascending process broad. Subopercle dorsal margin concave. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin square. Anguloarticular process long, extending beyond ventral margin of dentary. Mandible short, extended, length less than twice depth. Trigeminal nerve canals divided within the hyomandibula. Posterior lateral line fenestra contacting posterodorsal margin of hyomandibula. Cranial fontanels closed in juveniles and adults. Frontal shape narrow, width at fourth infraorbital less than that of parietal, anterior margin of straight, continuous with margins of adjacent roofing bones, postorbital process broad, more than two times width of supraorbital canal. Lateral ethmoid absent. Parietal rectangular, length less than width. Parasphenoid anteroventral portion gracile, extending ventral to lateral margin of parasphenoid, posterior processes narrow. Prootic foraminae separate for cranial nerves Vp and V2–3 +VII. Adductor mandibula muscle undivided at insertion, intermuscular bones absent. All basibranchials unossified. Gill rakers not contacting gill bar. Pectoral with 11–16 (mode 14) rays, medial radial large. Mesocoracoid elongate, length more than four times width.

Cleithrum broad, ventral margin curved, anterior limb long, more than 1.8 times ascending limb, deeply incised on its anteroventral margin, without large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity of moderate length, with 31–34 (mode 33) precaudal vertebrae. Rib five robust along its entire extent, less than three times width of rib six. Hemal spines present. Displaced hemal spines absent. Length anal-fin pterygiophores equal to or longer than hemal spines. Anal fin with 141–259 (median 192) rays. Lateral line ventral rami 14–28 (median 22). Caudal appendage short, less one-half length of pectoral fin. Single hypaxial electric organ along entire ventral margin of body. Three rows of electroplates near caudal insertion of anal fin.

Color in Alcohol: Bands irregular in shape, width and color, on specimens and among individuals. Ground color tan ventrally grading to darker brown or olive green dorsally in adults, pale yellow throughout in smaller specimens. Many obliquely-oriented, chocolate-colored bands with wavy, irregular margins on lateral surface from nape and to tip of caudal appendage, occurring singly or as band-pairs, increasingly divided and irregular with size (21–29 mode 28). Pale interbands less than one-third width of dark bands at mid-body. Bands rarely divided dorsally or ventrally to form X- or inverted Y -shaped patterns. Band-interband contrast increases ventrally and caudally, fades with growth (juveniles> 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).

Figures

FIGURE 2. Geographic distributions of the materials examined from two species of the G. tigre clade of the southern Neotropics. Specimensfrom all localities were personally examined and identified by the authors.

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).

FIGURE 8. Scatterplots of the variation on salient characters separating G. cuiaand G. c. australis. A. Head length (%TL) vs. total length (mm).B. Body depth (%HL) vs. head length (mm). C. Head depth (%HL) vs. head length (mm).

FIGURE 9. Habitat and live appearance of G. cuia. A. The type locality of G. cuia, Lagoa Verde, Itapuã State Park, Viamão, RioGrande, do Sul,Brazil (30°22’52”S, 051°01’25”W).Photo:Diego Cognato.B. Close-upphotoof the headof a live G.cuia. Photo:Will Crampton. C. Full-body photo of of alive G.cuia. Photo:Will Crampton.

FIGURE 10. Characterization of the electric organ discharges of Gymnotus carapo australis and Gymnotus cuia. A. Head-totail recorded EOD waveforms for Gymnotus carapo australis(black) and Gymnotus cuia (red) from Rio Grande do Sul, Brazil. Note the invariable presence of the P-1 and P3 phasesin the waveform in G.carapo australis but not G.cuia. B. Power spectral density (PSD) plots for Gymnotus carapo australis (black) and Gymnotus cuia (red) from Rio Grande do Sul, Brazil. Note the higher peak power frequency in G. carapo australis.