Gymnotus carapo

Gymnotus carapo sensu-stricto Linnaeus (Fig. 1, Tables 2 and 3) Gymnotus carapo sensu-stricto Linnaeus Gymnotus carapo (Linnaeus 1758): 246 (in part) [type locality: America]. Gymnotus albus (Pallas 1769): 35 [Surinam]. Gymnotus brachiurus (Bloch 1786): 61, plate 157, fig. 1 [Brazil]. Gymnotus fasciatus (Pallas 1767): 35 [Brazil: Roraima, Rio Branco]. Gymnotus putaol (Lacépède 1800): 145, 176 [Brazil]. Syntypes: Collected in the first half of the 18th Century near Paramaribo, Surinam (Lönn- 1896:23; Fernholm & Wheeler 1983:216-217; Wheeler 1991:162-163, fig. 6): NRM 64 (1), 262 mm;NRM 8224 (1), 331 mm;UUZM Linn. coll. 56 (1), 293 mm. Diagnosis. Gymnotus carapo s.s. differs from all members of the G. carapo species group except G. arapaima in possessing a color pattern composed of 16-27 [mean 22] dark obliquely oriented pigment bands or band-pairs, with irregular wavy margins, often broken into spots above lateral line on anterior half of body (shared only with G. arapaima and G. diamantinensis), without large pale blotches on head. Gymnotus carapo s.s. further differs from all members of the G. carapo species group in the following unique combination of characters: 1, circular scales, about as long as wide above lateral line at midbody; 2, two laterosensory canal pores in dorso-posterior corner of preopercle (in specimens 120-400 mm); 3, deep body (BD 9.7-12.1% TL [mean 10.2%, n=101] vs. 5.5-9.4% [mean 6.3- 9.0%); 5, head length moderate to long (HL 10.2-13.9% TL [mean 12.3%, n=99] vs. 7.9- 10.1% or 14.0-14.2%); 6, moderate size of scales over anal-fin pterygiophores (APS 7-12 [mode 8, n=50] vs. 5-7 or 12-16); 7, moderate number of lateral line scales to first ventral ramus (PLR 40-56 [mode 46, n=65] vs. 34-43 or 57-78); moderate number of precaudal vertebrae (PCV 33-37 [mode 33, n=50]; relatively few ventral lateral line rami (VLR 6-27 [mean 8, n=50] vs. mean 10-51); no dorsal lateral line rami. Gymnotus carapo s.s. can be distinguished from sympatric G. arapaima in the Western Amazon in possessing: 1, fewer pored lateral line scales to first ventral lateral line ramus (PLR 44-54 [mode 48, n=14] vs. 53-64 in G. arapaima [mode 57, n=27]); 2, fewer scales over anal fin pterygiophores (APS 8-10 [mode 9, n=14] vs. 10-13 in G. arapaima [mode 12, n=31]); and, 3, smaller size (maximum TL 418 mm, rarely more than 350 mm vs. 550 mm in G. arapaima). Description. Fig. 1 illustrates head and body shape and pigment patterns. Morphometric data in Table 2, and meristic data in Table 3. Body size large, to 418 mm. Sexual maturity at about 280 mm in males and 270 mm in females. Sexually monomorphic in both immature and breeding condition. Scales circular or slightly ovoid, present on entire postcranial portion of body from nape to caudal appendage. Gape size in mature specimens large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin fleshy and bulbous with thick pad of electroreceptor organs and support tissues overlying tip of snout and oral jaws. Anterior narial pore partially or entirely included within gape in large narial fold. Anterior nares large, subequal to diameter of eye. Circumorbital series ovoid to tear-drop shaped. Ethmoid region between anterior nares broad, its anterior margin rounded. Eye position lateral, lower margin of eye dorsal to horizontal with rictus. Premaxilla with 11-16 (mode 14, n=10) teeth disposed in single row along outer margin, arrow-head shaped anteriorly, conical posteriorly. Median margin of premaxilla curved. Maxilla-palatine articulation near anterior tip of mesopterygoid. Maxilla orientation vertical. Maxilla rod-shaped, narrow distally with a straight ventral margin. Maxilla length equal to about width of 4-6 dentary teeth. Dentary with one row of 16-19 (mode 17, n=4) teeth, 2-4 arrow-head shaped anteriorly, all others conical posteriorly. Dorsoposterior and ventroposterior dentary processes abut at midlength of bone. Dentary ventroposterior process almost as long as dorsoposterior process. Dentary dorsoposterior process narrow distally. Dentary ventral margin with a narrow lamella, its depth less than posterior process. Anteroventral margin of dentary rounded in lateral view, without a hook. Dorsal margin of opercle straight or slightly convex. Texture of dorsal operclar process lamellar or rugose. Dorsal opercular crest absent or small. Posterior margin of opercle smooth, entire, without spines or processes. Ventral ridge field of opercle broad. Dorsal ridge field of opercle long, more than half width of opercle. Dorsoposterior laterosensory ramus of preopercle with two superficial pores. Preopercle with anteroventral notch. Margin of preopercular medial shelf entire. Median shelf of preopercle large, more than half width of symplectic. Ascending process of mesopterygoid robust, long, its base shorter than its length. Mesopterygoid ascending process curved. Tip of mesopterygoid ascending process simple. Metapterygoid superior and inferior portions approximately equal in size. Dorsal margin of interopercle with broad ascending process. Dorsal margin of subopercle concave. Posterior margin of retroarticular square. Retroarticular with an arched lamella posteriorly, forming a small canal. Anguloarticular process long, extending beyond ventral margin of dentary. Mandible long, extended, its length more than twice its depth. Hyomandibular trigeminal canals (supraorbital, infraorbitral), connected. Posterior lateral line fenestra contacting dorsoposterior margin of hyomandibula. Cranial fontanels closed in juveniles and adults. Anterior margin of frontal straight, continuous with margins of adjacent roofing bones. Frontal postorbital process broad, more than two times width of supraorbital canal. Frontal shape narrow, width at fourth infraorbital less than that of parietal. Lateral ethmoid absent. Parasphenoid posterior processes narrow. Parietal rectangular, its length less than width. Pterosphenoid anteroventral portion robust, extending ventral to lateral margin of parasphenoid. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula undivided at insertion. Adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Basibranchial 5 unossified. Pectoral fin of moderate size, with 14-16 rays. Pectoral medial radial large. Mesocoracoid elongate, its length more than 4 times width. Postcleithrum thin, discoid or sickleshaped. Cleithrum narrow, with a straight ventral margin. Anterior limb of cleithrum long, more than 1.8 times ascending limb. Cleithrum deeply incised on its anteroventral margin. Cleithrum without large facet for insertion of muscle from supracleithrum. Body cavity of moderate length, with 30-35 (mode 33) precaudal vertebrae. Rib 5 robust along its entire extent, less than 3 times width of rib 6. Hemal spines present. Displaced hemal spines absent. Anal fin of moderate length, with 217-260 rays. Multiple anal-fin ray branching posterior to rays 10-17. Lateral line ventral rami 4-27 (left or right). Lateral line dorsal rami absent in adults. Length anal-fin pterygiophores equal to or longer than hemal spines. Caudal appendage short, less 0.5 times length of pectoral fin. Single hypaxial electric organ, extending along entire ventral margin of body. Three or four (mode four) rows of electroplates near caudal insertion of anal fin. Color in alcohol. Band appearance highly irregular in shape, width, arrangement, and color, both on and among individuals. All specimens share the following color features: ground color khaki yellow ventrally grading to pale brown dorsally in adults (200-300 mm), and pale yellow throughout in smaller specimens 16-23 (mode 21) obliquely oriented chocolate-colored bands on lateral surface extending from nape and pectoral-fin base to tip of caudal appendage. Bands occur singly and as band-pairs with bands becoming increasingly divided and irregular with size. Band-inter-band margins irregular and wavy. Bands divided dorsally or ventrally to form X or inverted Y-shaped patterns. Bandinter-band contrast increases ventrally and caudally and fades with growth; juveniles less than 150 mm clearly banded with distinct band margins, specimens 200-300 mm faintly banded, and some specimens over 250 mm unbanded except very faintly in posterior 1/3 of body. Pale inter-bands about 1/3 width of dark bands at mid-body. Bands of juveniles more homogenous in shape and pigment intensity, with more clearly defined margins. Two to three bands from either side meet at ventral midline, between anus and anal-fin origin. One to three bands posterior to last anal-fin ray. Head never banded, spotted, or blotched, its ground color dark brown dorsally grading to lighter brown ventrally, with numerous minute chromatophores speckled over branchiostegal membranes and ventral surface of head. Operculum with a rosy hue from underlying gills in live juveniles. Pectoral-fin rays brown, interradial membranes hyaline. Analfin membrane divided into two parts along body axis in adults: anterior 80% dark brown, charcoal gray or black, posterior 20% translucent. Specimens fixed in 10% formalin and preserved for 1-5 years in 70% ethanol maintain approximate colors of life, although darker pigments tend to pale with time. Color variation not known to be correlated with sex or structure of electric organ discharge. Color in life. Ellis (1913:120) provides an accurate description of living specimens of G. carapo: “In life the body is a translucent flesh-color or pale yellow, varying to a distinct pink in the parts rich in blood. The stripes and markings are blue or green, giving the fish a purplish or olive-green cast. The color may be deepened or lightened slightly by the expansion and contraction of the chromatophores.” Geographic variation. Six allopatric populations of G. carapo s.s. are recognized on the basis of the mean or modal values of several morphometric and meristic traits (Table 4). Gymnotus carapo s.s. from the Eastern Amazon (G. carapo EA) is found downstream from Manaus, in the lower-most region of the Rio Negro basin near Manaus, and in the Trombetas, Tapajós, and Tocantins basins. Gymnotus carapo EA is most similar in overall appearance to G. carapo from the Parnaíba and Itapicuru basins in the Brazilian state of Piauí (G. carapo PI), from which it differs on average by: 1, a longer head (HL 11.7-13.6% TL [mean 12.7%; n=15] vs. 10.2-12.2% [mean 11.4%, n=8]); 2, a flatter head (HD 50.8- 60.9% HL [mean 55.2%, n=16] vs. 58.3-64.8% [mean 61.0%, n=8]); and 3, a shorter snout (PR 60.0-65.5% HL [mean 62.3%, n=16] vs. 63.2-67.6% [mean 65.5, n=8]). Gymnotus carapo PI can be distinguished from G. bahianus by possession of: 1, oblique pigment bands (vs. spots or no dark pigments) on the anterior portion of the body; 2, a longer snout (PR 35-38% HL [mean 37%, n=8] vs. 33-36% [mean 35%, n=23]); 3, a wider mouth (MW 42-46% HL [mean 44%, n=8] vs. 35-45% [mean 40%, n=23]); 4, a longer postorbital region (PO 63-68% HL [mean 66%, n=8] vs. 60-65% [mean 62%, n=16]). Gymnotus carapo from the Rio Branco basin in the Brazilian state of Roraima (G. carapo RO) differs on average from other populations of G. carapo s.s. by: 1. a flatter head (mean HD 53% HL [n=10] vs. means 55-63% [n=89]); 2. a narrower head (mean HW 54% HL vs. means 56-61% [n=91]); and, 3. a longer body cavity (PCV 35-37 [mode 34, n=7] vs. modes 33-35 [n=40]). Gymnotus carapo from the rivers of the Guianas Shield, the Río Orinoco Basin and Island of Trinidad (G. carapo GU) is most similar in overall appearance to G. carapo RO, from which it differs on average by characters listed above. Gymnotus carapo from the Western Amazon (G. carapo WA) is known from the Rio Tefé, Japurá and Javarí drainages of Brazil, the Río Napo drainage of Ecuador, and the Río Nanay, Pastaza and Ucayali drainages of Peru. Gymnotus carapo WA is readily distinguished from all other populations of G. carapo in that the anterior half of the anal fin is black (vs. gray or brown; the anterior half of the anal fin is also black in G. arapaima). Gymnotus carapo from the Rio Madeira basin (G. carapo MD) is found in the Rio Jamarí and Machado drainages of Brazil, the Río Mamoré, Guaporé, and Beni drainages of Bolivia, and the Río Madre de Dios drainage of Peru. Gymnotus carapo MD is most similar in overall appearance to G. carapo WA, from which it differs on average by: 1, longer anal-fin pterygiophores and smaller overlying scales (APS 10-12 [mode 11, n=4] vs. 8-10 [mode 9, n=14]); 2, fewer posterior lateral line scales (to the first ventral lateral line ramus, PLR 40-49 [median 44, n=8] vs. 44-54 [median 48, n=14; total, PLL 84-98 [mean 85, n=4] vs. 110-128 [mean 120, n=14); 3, gray or brown (vs. black) color of the anterior half of the anal-fin. Electric organ discharge. Electric organ discharge waveform with total duration of approximately 1.1 - 1.5 ms comprising four phases with low-voltage pre and post potentials either side of dominant, approximately symmetrical, biphasic component. Distribution. A map with the distribution of identified lots of G. carapo s.s. is provided in Fig. 2. Gymnotus carapo s.s. is known from the Amazon and Orinoco Basins below c. 500 m elevation, the Island of Trinidad, drainages of the Guyanas Shield, and Atlantic drainages of northeastern Brazil (including the Ríos Pindaré, Itapicuru and Parnaíba). Gymnotus carapo s.s. is not known from Middle America, Trans-Andean (Pacific Slope, Ríos Atrato, Magdalena, Maracaibo), São Francisco, or Paraguay-Paraná river systems, the Rio Negro basin above Manaus (excl. Rio Branco), or the Atlantic drainages of Brazil east of Fortaleza or south of Recife. Ecology. Gymnotus carapo s.s. occurs in shallow waters with little or no flow in both floodplain and non-floodplain habitats throughout its range. In floodplains, juvenile specimens are found in patches of floating macrophytes along channel and lake margins. Adults occur in floating macrophytes, shallow waters and seasonally flooded forests. G. carapo s.s. undertakes aerial respiration by gulping atmospheric air into the hypervascularized posterior chamber of the gas bladder (Liem et al. 1984). Juvenile G. carapo s.s. feed primarily on small aquatic insects and crustaceans; especially chironomid larvae, Odonata and Coleoptera larvae and choncostraca. Adults prey on larger animals such as shrimps and fishes. Gymnotus carapo s.s. breeds during the wet season or period of rising flood waters (pers. obs.) and has been reported to mouth brood (Kirschbaum & Wieczorek 2002). Populations from Trinidad are known to undertake nesting and paternal care (Hopkins pers. com.). Unlike most gymnotiform fishes, G. carapo s.s. is occasionally sold in fish markets due to its substantial size, abundance and its ease of capture with baited hooks. Further notes on the ecology of G. carapo s.s. are provided in Crampton (1996b) and Alves-Gomes (1997). Remarks. The original description of G. carapo by Linnaeus (1758) was based in part on Artedi (1738), itself based on Marcgraf (1648), and in part on specimens in the Uppsala and Adolphi Friderici collections, now in the Ulriksdal Collection deposited at the NRM (Holthuis 1959; Hoogmoed 1973). Marcgraf’s description was based on material from the Dutch colonial region of northeastern Brazil; the current location of this material, if it still exists, is unknown (Ihering 1914). The overall species composition of South American fishes in the Uppsala and Adolphi Friderici collections indicates that these materials are from Surinam (S. Kullander pers. comm.). The specimens of G. carapo examined by Linnaeus are inferred to have been collected in the 18th Century near Paramaribo, Surinam, possibly by Dahlberg and Rolander. The type locality of G. carapo is here amended from “America” (Linnaeus 1758) to “Surinam.” Materials examined. 57 lots bearing 170 specimens are presented by Albert (2001); an additional 128 lots bearing 575 specimens (33-418 mm) are presented here. BOLIVIA. Beni: UF 82470 (2), 170-218 mm, Río Mamoré, Río Ibaré, Cercado, Arroyo San Javier (14°38'S, 64°53'W). UF 82485 (1), 360 mm, Río Mamoré, Río Ibaré, Cercado, 20 km N San Javier (14°28'S, 64°56'W). UF 82510 (1), 241 mm, Río Mamoré, Río Ibaré, Cercado, 25 km N San Javier (14°24'S, 64°56'W). UMMZ 204771 (5), 44-51 mm, Río Guaporé, Rio Itenez, 3 km S. Costa Marquez, Brazil (12°30'S, 64°17'W). UMMZ 66433 (2), 215- 331 mm, Río Beni, Lago Rogoagua (13°57'S, 66°58'W). Santa Cruz: UF 82191 (1), 187 mm, Río Guaporé, Río San Pablo, Río San Diablo, Velasco, 71 km N. San José de Chiquitos(17°18'S, 60°35'W). UF 82211 (2), 196-205 mm, Río Guaporé, Río San Pablo, Chiquitos, Comunidad La Esperanza, ca. 40 km N. San José de Chiquitos (17°25'S, 60°47'W). BRAZIL. Amapá: INPA uncat. (3), 33-81 mm, Rio Araguari, Bacapnari (01°15'N, 49°55'W). Amazonas: Alvarães: INPA 14227 (1, part), 385 mm, Presidente Figueiredo: Rio Urubu, Igarapé do Gavião, Fazenda Esteio (approx. 01°16'S, 59°49'W). INPA 21082 (1), 157 mm, Rio Japurã, Lago Amanã, Juã Grande (02°29'S, 64°49'W). MZUSP 75168 (1), 119 mm, Tefé: Rio Tefé, Ilha do Martelo (03°46'49"S, 64°59'29"W). MZUSP 76061 (1), 260 mm, Rio Tefé, Lago Tefé, Cabeçeira do Lago Tefé (03°34'35'S, 64°59'19"W). MZUSP 76062 (1), 94 mm, Rio Tefé, Lago Tefé, Ressaca do Socorro (03°19'11"S, 64°41'46"W). MZUSP 76063 (1), 298 mm, MSDR, Ressaca da Vila Alencar (03°07'42"S, 64°48'02"W). MZUSP 76064 (1), 253 mm, MSDR, Cano do Lago Mamirauá (03°04'26"S, 64°48'39"W). MZUSP 76066 (2), 97-136 mm, MSDR, Lago Secretaria (03°06'44"S, 64°48'01'W). Benjamin Constante: UMMZ 230734 (2), 190 - 210 mm, Rio Solimões, Rio Cayari (approx. 04°22'S, 70°02'W). Mato Grosso: Aripuanã: INPA 4383 (22), 42-188 mm, Rio Aripuanà, Igarapé do Aeroporto (approx. 10°10'S, 59°27'W). INPA 6383 (7), 139-197mm, same locality as INPA 4283. INPA 6388 (1, part), 292mm, same locality as INPA 4283. INPA 6392 (4), 140-190 mm, same locality as INPA 4283. INPA 6395 (2), 122-127 mm, same locality as INPA 6391. INPA 11554 (1), 145 mm, Rio Aripuanã, Praia Grande, 2 km below Cachoeira Dardanelos. INPA 6406 (26), 38-166 mm, same locality as INPA 4283. INPA 6407 (9), 107-313 mm, same locality as INPA 4283. INPA 6408a (9), 96-223 mm, same locality as INPA 4283. INPA 11549 (1), 230 mm, same locality as INPA 4283. INPA 11551 (4), 119-198 mm, same locality as INPA 4283. INPA 11552 (1), 182 mm, same locality as INPA 4283. INPA 11558 (1), 173 mm, Rio Aripuanã, Igarapé do Guaribal, 5 km below Cachoeira Dardanelos. INPA 11560 (11), 120-200 mm, same locality as INPA 4283. INPA 19954 (1), 135 mm, same locality as INPA 4283. INPA 6391 (8), 108-170 mm, Rio Aripuanà, 10 km above Cachoeira Dardanelos. Pará: Oriximinã: INPA 6379 (1), 229 mm, Rio Trombetas, Cachoeira Porteiro (01°05'S, 57°02'W). INPA 6385 (1), 164 mm, Rio Trombetas, Igarapé do Caxi-Pacoré. INPA 6393 (12), 97-220 mm, Rio Trombetas, BR 163, km 10-13. INPA 6400 (1), 96 mm, same locality as INPA 6379. INPA 6402 (1), 110 mm, same locality as INPA 6393. INPA uncat. (2), 89-107 mm, same locality as INPA 6393. MZUSP 30008 (8), 173-253 mm, Rio Trombetas, Rio Itacaiunas, Caldeirao, Igarapé do Pojuca (approx. 00°45'S, 56°13'W). MZUSP 30013 (1), 240 mm, Rio Trombetas, Igarapé do Paraíso. Parauapebas: MCZ 45189 (19), 133-210 mm, Ilha de Marajó, Rio Tocantins, Rio Arari, Cachoeira do Arari (01°01'S, 48°58'W). MZUSP 30025 (7), 165-237 mm, Rio Tocantins, Rio Itacaiuna, Serra Norte, Serra dos Carajás (approx. 05°05'S, 50°22'W. Tucurui: INPA 6378 (1), 315 mm, Rio Tocantins, Icangui. INPA 6380 (1), 246 mm, Rio Tocantins, Tucurui (04°25'S, 49°32'W). INPA 6386 (1), 157mm, same locality as INPA 6380. INPA 6382 (1), 418 mm, Rio Tocantins, Cameta (02°15'S, 49°30'W). INPA 6396 (1), 238 mm, Rio Tocantins, Jatubah. INPA 6405 (7), 65-125 mm, same locality as INPA 6382. Piauí: AUM 20624 (3), 179-225 mm, Piauí, Rio Gurgueia, Rio Parnaíba, 4 km E. Bertolina. AUM 20689 (2), 95-138 mm, Piauí, Rio Gurgueia, 25km SW Urucui. AUM 2079 (4), 156-192 mm, Piauí, Parnaíba, between Santa Filomena and Jurumenha. AUM 20624 (3), 179-225 mm, Piauí, Rio Gurgueia, Rio Parnaíba. AUM 20689 (3), 95-138 mm, Rio Gurgueia, Rio Parnaíba, Piauí. Rondônia: INPA 1152 (2), 165-175 mm, Ariquemes, Rio Cadeiras, Igarapé Tracoazinho, Serra Pacaas Novos. MZUSP 30006 (10), 125-200 mm, Rio Branco, Cachoeira do Bem Querer. Roraima: Mucajaí: INPA 6381 (5), 111-175 mm, Rio Mucajaí, Estação Fé-Esperança. INPA 6384 (2), 105-127 mm, Rio Mucajaí. COLOMBIA. Meta: NRM 27717 (1), 235 mm, Río Meta, Rio Ocoa, Laguna Santa Clara, ca. 5 km S Villavicencio (approx. 04°09'N, 73°39'W). UF 26178 (39), 134-239 mm, Río Guatiquia-Meta, Caños Negros, ca. 9 km Villavicencio on road to Puerto Porfia (approx. 04°09'N, 73°39'W). UF 33245 (1), 200 mm, Río Meta, Rio Guamal, 7 km E. Río Guayuriba, just N. Guamal (approx. 03°52'N, 73°45'W). ECUADOR. Napo: FMNH 103329 (10), 33-320 mm, Río Napo, Río Tiputini (approx. 00°49'S, 75°31'W). FMNH 103334 (2), 48-64 mm, Río Napo, Río Aguarico, Laguna Zancudococha(approx. 00°17'S, 75°52'W). PERU. Loreto: IAAP uncat. (1), 367 mm, Río Amazonas, Maynas, nr. Iquitos (no locality data). MUSM 9274 (1), 136 mm, Río Ucayali, Contamana, Aguas Calientes (07°02'S, 74°14'W). MUSM 14482 (7), 118-198 mm, Río Napo, Río Aguarico, Maynas, PV Castaña (00°48'13''S, 75°14'24''W). NRM 27650 (1), 305 mm, Río Samiria, Maynas, right bank stream tributary between Caño Pastos and Hamburgo(05°12'S, 75°08'W). NRM 40772 (1), 91 mm, Río Maniti, Maynas, 50 km NE of Iquitos (03°29'S, 72°44'W). UF 116573 (2), 189-279 mm, Río Amazonas, Maynas, Río Nanay. UF 122820 (1), 275 mm, same locality as UF 116573. UF 122822 (1), 330 mm, same locality as UF 116573. UF 122825 (1), 158 mm, same locality as UF 116573. UF 122847 (