PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
108(4):662-678. 1995 
Gymnotus maculosus, a new species of electric fish 
(Chordata: Teleostei: Gymnotoidei) from Middle America, 
with a key to species of Gymnotus 
James Spurling Albert and Robert Rush Miller 
Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109-1079, U.SA. 
Abstract — A new species of gymnotoid knifefish, Gymnotus maculosus, is 
described from Pacific drainages of Middle America, from Chiapas, Mexico, 
to Costa Rica, and an Atlantic drainage in Nicaragua. Morphological, meristic, 
and pigmentation features are compared with congeners. Variation among the 
species of Gymnotus from many localities in South America remains to be 
analyzed for a robust hypothesis about numbers of species and their interre- 
lationships. A phylogenetic diagnosis of Gymnotus, and a key to the recognized 
species is provided. 
Resumen. — Se describe una nueva especie de anguila electrica, Gymnotus 
maculosus. Esta especie se encuentra en las vertientes Pacificas de Mesoam- 
erica desde Chiapas, Mexico, hasta Costa Rica, y en una cuenca Atlantica de 
Nicaragua. Se discuten y comparan caracteristicas morfologicas, meristicas, y 
de pigmentacion con otros miembros del genero. Para poder establecer el nu- 
mero de especies de Gymnotus y sus relaciones, es necesario un analisis de la 
variabilidad entre especies de diversas localidades en Sudamerica. Se provee 
una diagnosis filogenetica del genero Gymnotus y una clave de identificacion 
de las especies reconocidas. 
Gymnotus is the most widely distributed 
genus of American electric knifefishes (Te- 
leostei: Gymnotoidei). Members of the ge- 
nus range from the Rio San Nicolas of 
southeastern Chiapas, Mexico, south to the 
Rio de la Plata, Argentina (Eigenmann & 
Ward 1905, Eigenmann & Fischer 1914, Ei- 
genmann & Allen 1942, Miller 1966, Buss- 
ing 1985). Members of this lineage are ag- 
gressive, nocturnal predators who prefer 
small tributaries, lagoons, and backwater 
swamps, and in Middle America sometimes 
inhabit highland lakes. 
The systematic position and organization 
of Gymnotus are problematic. Gymnotus 
was proposed by Peter Artedi in 1738 to 
include the type species G. carapo Linnae- 
us. According to Ellis (1913) the original 
specimens were collected in the Guy anas. 
Ellis (1913) was the first to propose a for- 
mal hypothesis of interrelationships among 
the major gymnotoid lineages, placing 
Gymnotus and Electrophorus as the sister 
lineage to all other gymnotoids (Ellis 1913, 
Eigenmann & Fischer 1914). Ellis synony- 
mized all specimens of Gymnotus into the 
type species, G. carapo. 
There are presently thirteen described 
species of Gymnotus, of which five have 
been synonymized with the type species 
(Mago-Leccia 1994). Several additional 
species are recognized in museum collec- 
tions, however, so that the actual number of 
species may be substantially higher. De- 
scriptions of several of these species await 
the acquisition of sufficient samples from 
populations across their geographical range 
(Mago-Leccia 1994). Most specimens of 
Gymnotus in museum collections are iden- 
tified as G. carapo, regardless of their ap- 
pearance or origin. This is due, in part, to 
the wide geographical extent of this puta- 
VOLUME 108, NUMBER 4 
663 
Table 1. — Number of precaudal vertebrae in Gymnotus species. Counts from a total of 75 specimens are 
reported. 
30 
32 
34 
36 
38 
40 
42 
44 
46 
48 
50 
n 
Mode 
anguillaris 
5 
5 
38 
carapo 
6 
6 
38 
catanaiapo 
2 
2 
50 
coatesi 
3 
1 
4 
40 
cylindricus 
2 
15 
6 
23 
32 
maculosus 
1 
11 
9 
21 
32 
pedanopterus 
7 
7 
36 
stenoleucus 
4 
3 
7 
46 
Total 
3 
26 
15 
7 
7 
3 
1 
4 
3 
2 
75 
tive species, which is known from Guyana 
to the Rio La Plata basin and many inter- 
vening sites. Furthermore, color patterns, 
and body shapes of specimens referred to 
G. carapo vary widely across the range. 
The species diversity of Gymnotus is 
greatest in the Amazon basin, from where 
six species are recognized. Five of these 
species also inhabit the Upper Rio Orinoco 
basin (Mago-Leccia 1994). Gymnotus an- 
guillaris Hoedeman, originally described 
from Guyana, has also been collected from 
the Orinoco, Amazon, and La Plata basins. 
The other species have more restricted dis- 
tributions. Gymnotus coatesi LaMonte is 
known only from the western Amazonian 
lowlands of Brazil and Peru, G. inaequila- 
biatus (Valenciennes) is from the Rio de La 
Plata drainage, and G. pantherinus (Stein- 
dachner) from Atlantic drainages of south- 
em Brazil. 
Gymnotus also ranges into Middle Amer- 
ica. Understanding the biogeographic his- 
tory of Gymnotus in northwestern South 
America and Middle America is confound- 
ed by the complex geological history of the 
region (Bussing 1987, Pittman et al. 1993). 
Although the species diversity of Gymnotus 
has not been recently studied west of the 
Andes, there appear to be several unrecog- 
nized species inhabiting small coastal 
streams and rivers along the Pacific coast 
from Ecuador, north to Chiapas, Mexico. 
The purpose of this paper is to describe one 
of these species, discovered one of us 
(RRM). 
Methods. — Methods used herein are 
modified or elaborated from Lundberg & 
Mago-Leccia (1986), Fink (1989), and Fink 
& Machado- Allison (1992). Specimens ex- 
amined are listed in the Appendix. Museum 
acronyms are as presented by Leviton et al. 
(1985). Osteological data were taken from 
cleared and stained specimens using a mod- 
ified version of the enzyme technique of 
Taylor & Van Dyke (1985). Standardized 
dissection methods of small teleosts were 
used (Weitzman 1974). We follow Fink & 
Fink (1981) for bone nomenclature. All 
drawings were made with the aid of a Zeiss 
dissecting microscope, equipped with a 
camera lucida, and edited by means of a PC 
graphics editor. 
Counts of precaudal vertebrae (Table 1) 
and anal-fin rays (Table 2) were taken from 
radiographs. The number of precaudal ver- 
tebrae includes those of the Weberian ap- 
paratus; number of precaudal vertebrae is 
used here as a proxy for body-cavity length 
(Albert & Fink, in press). Body proportions 
reported include head length (HL), from 
posterior margin of bony operculum to tip 
of snout; postorbital head length (PO), from 
posterior margin of bony opercle to poste- 
rior margin of eye; preorbital head length 
(PR), from anterior margin of eye to tip of 
snout; body depth (BD), vertical distance 
from origin of anal fin to dorsal body bor- 
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PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Table 2. — Number of anal-fin rays in Gynmotus species. Counts from a total of 58 specimens are reported. 
155 
165 
175 
185 
195 
205 
215 
225 
235 
245 
255 
n 
anguillaris 
1 
2 
1 
1 
5 
carapo 
2 
1 
2 
1 
6 
catanaiapo 
2 
3 
1 
7 
coatesi 
2 
1 
1 
4 
cylindricus 
1 
1 
5 
3 
3 
1 
14 
maculosus 
2 
4 
2 
8 
pedanopterus 
1 
1 
1 
1 
7 
stenoleucus 
2 
3 
1 
1 
7 
Total 
2 
5 
3 
5 
4 
10 
8 
9 
5 
2 
1 
58 
der, with lateral line held horizontal; pec- 
toral-fin length (PI), from dorsal border of 
fin base where it contacts cleithrum to tip 
of longest ray; interorbital distance (lO), 
between dorsomedial margins of eyes; size 
of branchial opening (BO), from postero- 
dorsal to anteroventral extent of fold along 
anterior margin; pre-anal distance (PA), 
from anterior insertion of anal fin and pos- 
terior margin of anus. Body size is repre- 
sented by head length (HL) in millimeters. 
The use of head length as a rough measure 
of overall body length is discussed by Al- 
bert & Fink (in press). Specimens in which 
the caudal filament was obviously damaged 
and unrepaired were excluded from mea- 
surements of total length. 
Some measurements used in this report 
differ from those of earlier works on gym- 
notoids (Mago-Leccia 1978, 1994). Head 
length, for example, is defined as the dis- 
tance between tip of snout and posterior ex- 
tent of the bony opercle. Head length mea- 
sured from the posterodorsal termination of 
the branchial opening (Mago-Leccia 1978) 
is subject to greater preservation-induced 
artifact and was not used. Measures of pec- 
toral-fin length, postorbital length, and 
body depth reported here may also differ 
from results of previous studies. For these 
measurements, we attempted to use the un- 
ambiguous landmarks noted above to define 
endpoints. 
This report is part of a larger research 
effort by the first author on systematics and 
evolution of the Gymnotoidei. A total of 
more than 2400 specimens representing at 
least 80 gymnotoid species have been ex- 
amined (Albert 1995). Character polarities 
were determined from the hypothesis of re- 
lationships proposed by Albert (1995; see 
Discussion). 
Monophyly and Nomenclature of 
Gymnotus 
Gymnotus Linnaeus 1758 
Gymnotus Linnaeus 1758:246 (type spe- 
cies, by original monotypy, G. carapo 
Linnaeus 1758). 
Carapus Cuvier 1816 (nee Rafinesque): 
237. 
Giton Kaup in Dumeril 1856:201 (type spe- 
cies, by original monotypy, G. fasciatus 
Pallas 1767:35). 
Diagnosis. — Species of Gymnotus have 
multiple (13-50) pale oblique bands of re- 
duced melanophore density along lateral 
surface of body (obscured in some spe- 
cies); anterior narial opening located with- 
in gape such that pore opening faces an- 
teroventrally (also present in many rham- 
phichthyoids); anterior pharyngobranchial 
(associated with gill arch 3) unossified; all 
five basibranchials unossified; capacity to 
regenerate postcoelomic neural spines 
(Gayet & Meunier 1991); cyhndrical or 
barrel shaped electrocytes, without a stalk, 
their long axis oriented longitudinally 
(Bass 1986, fig. 1). 
Description. — The polarity of several 
VOLUME 108, NUMBER 4 
665 
characters useful in identifying specimens 
of the genus Gymnotus are ambiguous. 
Mesethmoid short and broad. Frontals 
broad. Extrascapular firmly articulated with 
cranium. Lateral ethmoids absent. Meso- 
pterygoid edentulous, bearing an ascending 
process. Infraorbital series represented by 
superficial bony tubes. Urohyal well devel- 
oped. Four broad branchiostegal rays, two 
anterior branchiostegals narrower than the 
others. Basihyal elongate and hollow. Basi- 
branchials not ossified. Three ossified phar- 
yngobranchials. Five epibranchials, fifth 
one cartilaginous. Gill-rakers small, dentig- 
erous plates, located on both margins of 
fourth branchial arch and on anterior mar- 
gin of fifth arch, and covered by connective 
tissue. Branchial openings large, branchios- 
tegal membrane united across isthmus. 
Posttemporal not fused with supracleith- 
rum. Mesocoracoid present. Coracoid not 
bearing ventral process. Four pectoral ra- 
dials. Lateral line complete. Presence of 
30-51 precaudal vertebrae. No displaced 
hemal spines. Anus not growing anteriorly 
during ontogeny. Anterior insertion of anal 
fin not extending anterior to vertical 
through posterior margin of pectoral fin. 
Anal fin confluent with tip of tail (rays of 
the posterior portion of anal fin are tightly 
aggregated and lie horizontally caudally, 
making it difficult to count the exact num- 
ber of rays other than in stained specimens 
or radiographs). 
Species of Gymnotus mature at moderate 
body sizes (approximately 150 to 400 mm 
TL), possess a cylindrical or subcylindrical 
body, and are completely covered by cy- 
cloid scales on the postcranial part of their 
bodies. In many species, color pigmentation 
patterns are formed by alternating bands of 
dark and pale oblique bands along the body 
axis. The band-interband contrast increases 
ventrally, and is generally more pronounced 
in juveniles (less than 100 mm TL). Al- 
though the number, width, and shape of 
these bands are variable, banding patterns 
have diagnostic value for several species 
(Mago-Leccia 1994). 
We follow Mago-Leccia (1994) in rec- 
ognizing the following species of the genus 
and their synonyms: 
Gymnotus carapo Linnaeus 
G. carapo Linnaeus, 1758:246 (type lo- 
cality: America). 
G. fasciatus Pallas, 1767:35 (type local- 
ity: Brazil). 
G albus Pallas, 1767:35 (type locaUty: 
Suriname). 
G brachiurus Bloch, 1787:61, plate 157, 
fig. 1 (type locality: Brazil). 
G putaol Lacepede, 1800:176 (type lo- 
cality: Brazil). 
G. cingulatus Brind, 1935 (type locality: 
Brazil). 
Gymnotus inaequilabiatus (Valenciennes) 
Carapus inaequilabiatus Valenciennes in 
D'Orbigny 1847:11, plate 14 (type lo- 
cality: Rio de La Plata, Argentina). 
Gymnotus pantherinus (Steindachner) 
Giton fasciatus van pantherinus Stein- 
dachner, 1908:129 (type locahty: San- 
tos, Brazil). 
Gymnotus coatesi LaMonte 
G coar^^/ LaMonte, 1935:1, fig. 1 (type 
locality: Rio Amazonas, Brazil). 
Gymnotus cylindricus LaMonte 
G. cylindricus LaMonte, 1935:2 (type lo- 
cality: Los Amates, Rio Motagua Ba- 
sin, Guatemala). 
Gymnotus anguillaris Hoedeman 
G. anguillaris Hoedeman, 1962a:55, fig. 
2 (type locality: Coropina Creek, Su- 
riname). 
G. coropinae Hoedeman 1962a:55, fig. 
Ic (type locality: Coropina Creek, Su- 
riname). 
Gymnotus cataniapo Mago-Leccia 
Gymnotus cataniapo Mago-Leccia 1994: 
90, fig. 100, table 9 (type locality: Rio 
Cataniapo, Amazonas, Venezuela). 
Gymnotus pedanopterus Mago-Leccia 
Gymnotus pedanopterus Mago-Leccia 
1994:92, fig. 98, table 10 (type locali- 
ty: Cano La Esmeralda, Rfo Orinoco, 
Amazonas, Venezuela). 
666 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASfflNGTON 
P*'^;^.^*^: 
.,'.^0^ltmi^^^> 
Fig. 1. Lateral view of Gymnotus maculosus, paratypes, USNM 134700, 185 and 195 mm TL, Rio Buena 
Vista 8 km W of Pajal, Departamento Santa Rosa, Guatemala. 
Gymnotus stenoleucus Mago-Leccia 
Gymnotus stenoleucus Mago-Leccia 
1994:94, figs. 99-101, table 11 (type 
locality: Rio Cataniapo, Amazonas, 
Venezuela). 
Gymnotus maculosus, new species 
Fig. 1-6 
Gymnotus carapo in part, Eigenmann & 
Fisher, 1914:235. Rivers and lakes on 
both slopes of Guatemala. 
Gymnotus carapus Carr & Giovannoli, 
1950:11-12. Rio Choluteca, Honduras. 
Gymnotus cylindricus Bussing, 1985, fig. 
36. 
Gymnotus sp. Miller, 1966:786 (Pacific 
slope of Middle America from Guate- 
mala to the Gulf of Fonseca). 
Gymnotus sp. Miller, 1986:129 (Pacific 
slope of Middle America between Te- 
huantepec and Guatemala). 
Gymnotus sp. Espinosa Perez et al., 1993: 
29 (Rio Usumacinta). 
Holotype.—UMMZ 230830, 191 mm 
TL. Diversion of channel from Maria Lin- 
da, 14°04'N; 90°37'W, c. 20 km. East of 
Escuintla, Departamento Santa Rosa, Gua- 
temala; collected by D. E. Rosen and R. M. 
Bailey, 27 March 1971. 
Paratypes.— \5MMZ 190783, 3 speci- 
mens, 176-203 mm TL, type locality. 
UMMZ 224128, 5 specimens, 158-222 
mm, Rio Higueron, Canas, Costa Rica. 
UMMZ 230354, 20 specimens, Rio Buena 
Vista, trib. of Rio Tigre, on road between 
Escuintla and Chiquimulilla, 8 km. West of 
Pajal, Departamento Santa Rosa, Guate- 
mala, 128-230 mm, 1946.IV. 18. USNM 
134700, 49 specimens, Rio Buena Vista, 8 
km. West of Pajal, Departamento Santa 
Rosa, Guatemala, 67-195 mm TL, 
1946.IV 18. TU 24965, 36 specimens, 60- 
260 mm TL, Boca del Rio Sapoa at Sapoa, 
Nicaragua. 
Diagnosis. — A gymnotid unique in pos- 
sessing numerous small brown spots, Vciry- 
ing in size from two to four times eye di- 
ameter, distributed over most of the body 
surface (Figs. 1, 2). The body lacks distinct 
oblique bands in both juveniles and adults. 
Scales above the lateral line large, 6-8 rows 
to the dorsal midline at about midbody. 
Description. — Figure 3 illustrates body 
shape. Body subcylindrical (its greatest 
width 0.61-0.84% BD); BD = 10-13% TL; 
dorsal profile of body almost straight, ven- 
tral profile slightly convex; head small, de- 
pressed, HL = 9.8-12.7% TL; PO = 58- 
64.5% HL; anterior nares tubular, partially 
concealed in labial groove; posterior nares 
round, and positioned close to eye; mouth 
VOLUME 108, NUMBER 4 
667 
Fig. 2. Lateral view of Gymnotus rnaculosus, paratype, TU 24965, 238 mm TL, Rio Sapoa at Sapoa, Nic- 
aragua. 
broad, gape large, rictus of mouth not 
reaching vertical through eyes; lower jaw 
protruding, teeth small, conical, in a single 
row in each jaw, with irregular second row; 
snout blunt, PR = 33.1-37.5% HL; lO = 
37.0-41.0% HL; origin of anal fin posterior 
to tip of pectoral fin, PA = 7.4-11.1% TL; 
branchial opening large, BO = 33.0-44.3% 
HL; nape without pale band; lateral line 
complete, paralleling main body axis; pec- 
toral fin small, rounded, PI = 43-48% HL; 
pectoral-fin rays ii+ 15-16 {n = 8); 30-34 
precaudal vertebrae (Table 1, mode = 32, n 
= 21); anus near vertical through branchial 
opening; anal fin short, 155-182 anal-fin 
rays (Table 2, mode = 169, n = 8). 
Color in preservative. — Ground color 
yellow to pale brown laterally on preserved 
specimens. Dorsum dark brown due to 
densely concentrated melanophores. Dark 
brown dorsally and laterally. Ground color 
overlaid by numerous brown spots on head 
and body, ranging in size from about 2 to 
4 eye diameters, and varying somewhat in 
Fig. 3. Diagrammatic representation of Gymnotus rnaculosus. (A) dorsal, (B) lateral, and (C) ventral view. 
Arrow indicates position of the anus. Scale bar equals 10 mm. 
668 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
pterotic supraoccipital 
parietal \ extrascapular \ exoccipital 
prootic \ \ \ \epioccipital 
frontal 
mesethmoid 
orbitosphenoid / F.Vi 
ventral ethmoid pterosphenoid 
F.VII 
F. int. carotid 
F.IX-X 
basiobcipital 
parasphenoid 
Fig. 4. Lateral view of neurocranium of Gymnotus maculosus, UMMZ 190531, 185 mm TL. Cartilage 
indicated by stippling. Abbreviations: F. V,, foramen of cranial nerve Vi (profundus); F. II-VI, foramen of optic 
tract and cranial nerves III (oculomotor), IV (trochlear), and VI (abducens); F. int. carotid, foramen of internal 
carotid artery; F. V2.3, foramen of V2 (superficial ophthalmic and maxillary) and V3 (internal mandibular) rami 
of trigeminal nerve; F VII, foramen of cranial nerve VII (facial); E IX-X, foramen of cranial nerves IX 
(glossopharyngeal) and X (vagus). Scale bar equals 1 mm. 
size and arrangement. Some specimens 
with spots arrayed into approximately 13- 
21 oblique lines, corresponding to oblique 
lateral bands of other species of Gymnotus; 
other specimens with smaller spots, arrayed 
into more than 40 oblique lines, or with 
spots arrayed in a somewhat random pat- 
tern. The organization of spot and pigment 
density is not a function of body size. Anal 
and pectoral fins without spots. Anal- and 
pectoral-fin rays and interradial membranes 
hyaline. 
Etymology. — From the Latin maculosus, 
meaning spotted, in reference to the con- 
spicuous color pattern possessed by this 
species. 
Distribution. — Gymnotus maculosus 
lives in freshwater streams of Middle 
America (Fig. 7). On the Pacific slope it 
ranges from the Rio San Nicolas (15°20'N, 
92°50'W), Chiapas, Mexico, south to trib- 
utary streams to the Gulf of Nicoya in 
northwestern Costa Rica (9°47'N, 
84°48'W). On the Atlantic slope it appears 
to be restricted to streams on the western 
slope of the Lake Nicaragua basin in Nic- 
aragua, the Rio Sapoa of northern Costa 
Rica, and the San Carlos and Sarapiqui 
drainages of northeastern Costa Rica. The 
seemingly disjunct distribution of G. ma- 
culosus in Fig. 7 is presumed to result from 
the lack of collections from Pacific slope 
drainages of El Salvador and Nicaragua. 
Remarks. — Gymnotus maculosus shares 
two characters of ambiguous polarity with 
G. cylindricus; absence of discrete oblique 
bands along the body, and short body cav- 
ity, with 31-35 precaudal vertebrae. 
Comparisons with other species. — Gym- 
notus maculosus can be separated from par- 
apatric members of G. cylindricus in the 
Lake Nicaragua basin by its unique color 
pattern, by its smaller interorbital distance, 
and by the larger size of scales above the 
lateral line. Specimens of G. cylindricus 
possess few if any small brown spots on the 
VOLUME 108, NUMBER 4 
A 
669 
B 
posttemporal 
supracleithrum 
cleithrum 
mesocoracoid 
scapula 
coracoid 
radiais 
Fig. 5. Pectoral girdle of Gymnotus maculosus, UMMZ 190531. (A) lateral view. (B) medial view. Cartilage 
indicated by stippling. Scale bar equals 1 mm. 
body. Although some specimens of G. cy- 
lindricus possess a mottled appearance, 
with low contrast, pale spots on the ventral 
portion of the body, only G. maculosus pos- 
sesses high contrast spots over the entire 
body. The interorbital distance of G. ma- 
culosus is 31-A\% HL, whereas that of G. 
cylindricus is 41-46% HL. Scales above the 
lateral line are larger in G. maculosus, with 
6-8 rows to the dorsal midline at about 
midbody, whereas those of G. cylindricus 
are smaller, with 10-12 rows above the lat- 
eral line at about midbody. 
Gymnotus maculosus can be separated 
from the other species of Gymnotus by its 
color pattern and meristic, features. Gym- 
notus maculosus has fewer precaudal ver- 
tebrae (30-34, n = 21; vs. 38, n = 6) and 
fewer anal-fin rays (155-182, « = 8; vs. 
190-222, n = 6) than does G. carapo. Un- 
like G. carapo, G. maculosus is spotted and 
does not have conspicuous oblique bands. 
Gymnotus maculosus can be separated from 
other spotted species of Gymnotus, G. in- 
aequilabiatus and G. pantherinus, by the 
same meristic characters used to separate it 
from G. carapo. 
Discussion 
Variation in characters examined. — Sev- 
eral body measurements vary among and 
between species of Gymnotus. Uses of body 
depth, head length, interorbital distance, 
and pectoral-fin length to identify species 
are noted in the key. Despite this variation, 
the characters used in the diagnoses do 
prove useful when making certain compar- 
isons. The deep body of G. inaequilabiatus 
(BD greater than HL), for example, can be 
used to separate it from all other South 
American species of Gymnotus (except 
some specimens of G. cataniapo) in which 
the BD is less than HL. Specimens of G. 
carapo and G. pedanopterus possess a long 
head (HL greater than 1 1.8% TL for spec- 
imens 100-250 mm TL) when compared to 
other species of Gymnotus. Although the 
snout length of most Gymnotus species 
ranges from PR - 32.5-38.0% HL, speci- 
670 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASfflNGTON 
hyomandibula opercle 
m eta pterygoid 
mesopterygoid 
palatine 
maxilla 
dentary 
anguloarticular 
subopercle 
retroarticular symplectic 
interopercle 
Fig. 6. Lateral view of suspensorium of Gymnotus maculosus, UMMZ 19053 L Cartilage indicated by stip- 
pling. Scale bar equals 1 mm. 
mens of G. anguillaris tend to have a longer 
snout (PR = 36.0^1.0% HL), and speci- 
mens of G. coatesi, G. cataniapo, G. pe- 
danopterus, and G. stenoleucus tend to 
have shorter snouts (PR = 28.5-36.5% 
HL). The anal fin of G. carapo and G. in- 
aequilabiatus tends to insert more anteri- 
orly than in other Gymnotus species (PA = 
55-86% HL vs. 72-1 12% HL). These mea- 
surements exclude two specimens of G. cy- 
lindricus with abnormally short PA distanc- 
es (31% and 46% HL). PA data for G. pe- 
danopterus and G. stenoleucus were not 
available for this study. The two species of 
Gymnotus from Middle America share a 
short pectoral fin (PI = 38.0^7.5% HL) 
with the Suriname specimens of G. carapo, 
and with the slender species G. cataniapo, 
G. pedanopterus, and G. stenoleucus. 
Body proportions of Gymnotus carapo in 
South America vary considerably. Speci- 
mens examined from Suriname can be dis- 
tinguished from those in the Amazon basin 
by having a deeper body (BD = 11.5- 
12.5% TL vs. 10-11% TL) and a shorter 
pectoral fin (PI = 38-^5% HL vs. 46-57% 
HL). The anal-fin origin also tends to be 
more remote from the anus in the Suriname 
specimens (PA = 9.5-11.0% HL vs. 6.5- 
10.0% TL). Specimens collected west of 
the Andean cordillera in Colombia, from 
the Rio Atrato basin and the Pacific drain- 
age at Pizarro, possess the two diagnostic 
traits of G. carapo: a long head (HL = 
11.8-12.5% TL) and a clear anal-fin mem- 
brane at the posterior end of the fin. Mea- 
surements of these specimens (N = 5) re- 
veal that they have the more slender body 
(BD = 10.0-10.2% TL) and longer pectoral 
fin (PI = 45.2-58.3% HL) of G. carapo 
from the Amazon, and the posterior origin 
of the anal fin (PA = 9.0-11.2% TL) of G. 
carapo from Suriname, and of the other 
Gymnotus species. 
VOLUME 108, NUMBER 4 
671 
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^ 
14° 
^v-**^ 
Ss 
^\Uj 
\jj /J \"^ 
f ■" 
14° 
12' 
- 
x^ 
i ' ' 
12° 
in° 
^i^^^^^ 
\^ 
10° 
■ Gymnotus cyJJnc/rJcus 
• Gymnotus macuJosus 
1 
1 
1 
y^^\^fy^. 
1 1 
93° 91° 
89° 
87° 
85° 
83° 
Fig. 7. Geographic distribution of the two Middle American species of Gymnotus. Type localities indicated 
by hollow symbols. The absence of G. maculosus from the Pacific slope of El Salvador and Nicaragua is due 
to sampling bias. 
Although color patterns are of use in 
identifying species of Gymnotus, certain as- 
pects are variable (Nijssen & Isbriicker 
1968, Mago-Leccia 1994). The trans-An- 
dean specimens of G. carapo, for example, 
differ from other populations G. carapo in 
possessing narrow pale bands. This aspect 
of coloration is otherwise only observed in 
elongate, slender species of Gymnotus (see 
below). Another example of variable color 
pattern is G. anguillaris from the Lawa 
River, Suriname, which resemble G. carapo 
in their dusky brown ground color and in 
possessing more than 23 alternating pale 
and dark bands. The pale bands are narrow- 
er than the dark bands only on the posterior 
end of the body. Specimens of G. anguil- 
laris from other localities, however, ranging 
from Guyana to Paraguay, more closely re- 
semble the description of the type specimen 
in which the pale bands are more narrow 
along the entire length of the body (Hoede- 
man 1962a). 
Comments on the interrelationships of 
Gymnotus. — Species diversity and system- 
atics of the Gymnotoidei have received 
considerable attention in recent years 
(Mago-Leccia 1978, 1994; Lundberg and 
Mago-Leccia 1986; Triques 1993; Gayet et 
al. 1994; Alves-Gomes et al. 1995; Albert 
1995). The results of Albert's (1995) study 
support Ellis's (1913) hypothesis that Gym- 
notus and Electrophorus form a monophy- 
letic group, the Gymnotoidea (Gymnotoidei 
of Mago-Leccia 1978), which is itself the 
sister lineage to other gymnotoids (Albert 
1995, fig. 1; Albert & Fink 1995, fig. 2). 
The Gymnotoidea is diagnosed by 14 char- 
acters. Gape large, extending to vertical 
through posterior nares; premaxilla large. 
672 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASfflNGTON 
articulating head of maxilla oriented ante- 
riorly; lateral margin of premaxilla pro- 
duced into a posterior process; ventral mar- 
gin of descending maxillary blade with a 
sharp angle about two-thirds distance to its 
tip; base of lateral ethmoid narrow; cranial 
fontanels closed in adults; m. adductor 
mandibulae undivided bundle at origin; lat- 
eral portion of valvula cerebelli larger in 
cross sectional area than medial portion at 
isthmus; depression on dorsal surface of ba- 
sihyal; ventral process of coracoid absent; 
anal-fin pterygiophores long, more than 
one-third total body depth; caudal fin or fil- 
ament absent, caudal anal-fin rays extend to 
tip of tail; body cavity long, more than 30 
precaudal vertebrae; posterior chamber of 
gas bladder elongate, passing between he- 
mal arches of postcoelomic axial skeleton 
and musculature. 
Although a formal hypothesis of relation- 
ships among species within Gymnotus is 
beyond the scope of this paper, the data 
used in this study may be used to divide 
Gymnotus into three species-groups, on the 
basis of color pattern and general body pro- 
portions. Because the characters used to 
recognize these species-groups are not po- 
larized, the monophyly of these groups and 
their interrelationships are ambiguous. 
One species-group is composed of elon- 
gate, slender species, with a BD less than 
1 1 % TL. Members of this group also pos- 
sess a color pattern consisting of alternating 
dark and pale bands, in which the pale 
bands are narrower than the dark bands, and 
the dense brown or grey dark bands extend 
onto the dorsum. Gymnotus anguillaris is 
the most widely distributed member of this 
group and exhibits the greatest variation in 
these characters. Members of the second 
species-group have deeper bodies, with a 
BD greater than 11% TL, and the alternat- 
ing bands of heavy and light pigmentation 
are of about equal width, grading to a dusky 
brown on the dorsum. This group includes 
the type species G. carapo. The third spe- 
cies-group is composed of the two exclu- 
sively Middle American species of Gym- 
notus. These species lack the oblique non- 
pigmented bands of South American Gym- 
notus species, and have a shorter body 
cavity (31-35 precaudal vertebrae), char- 
acteristics regarded to be relatively ple- 
siomorphic among gymnotoids (Albert 
1995). 
Based on both phylogenetic and biogeo- 
graphic considerations, the Gymnotidae can 
be presumed to have originated in South 
America (Lundberg 1993). There is no ev- 
idence, however, that the Middle American 
species of Gymnotus are derived from an 
extant South American congener. If the 
Middle American species-group were to be 
identified as the sister taxon to other species 
of Gymnotus, the presence of an elongate 
body cavity with more than 35 precaudal 
vertebrae, would be evidence for the mono- 
phyly of the G. carapo and G. anguillaris 
species-groups. Unfortunately, the polarity 
of body cavity length in Gymnotus is am- 
biguous. The immediate outgroup taxon, 
Electrophorus, does not possess caudal ver- 
tebrae at all; the body cavity and gas blad- 
der extend to the caudal end of the animal, 
hemal spines do not form, and the hemal 
arches do not meet along the midline. The 
next outgroup is not elongate; species of 
Sternopygus, which retain a relatively ple- 
siomorphic gymnotoid morphology, pos- 
sess fewer precaudal vertebrae than any 
species of Gymnotus. In fact, the phyloge- 
netic distribution of the number of precau- 
dal vertebrae among extant gymnotoid taxa 
indicates that the plesiomorphic condition 
for the group is 17-19 (Albert 1995). 
The polarity of oblique depigmented 
bands in Gymnotus is also ambiguous. 
Many rhamphichthyoid species possess al- 
ternating color bands, but these bands are 
vertical regions of pigment investing a non- 
pigmented background. Narrow bands are 
not present in Electrophorus, Sternopygus, 
or the plesiomorphic hypopomid Hypopo- 
mus (Albert 1995). Furthermore, the pre- 
sumed absence of oblique bands in the Mid- 
dle American species of Gymnotus is not 
entirely clear; the pattern of spots in some 
VOLUME 108, NUMBER 4 
673 
specimens of G. maculosus is somewhat 
similar to the obHque bands of other Gym- 
notus, in position, orientation, and number. 
Biogeography of Middle American Gym- 
notus. — The geographic distribution of 
Gymnotus is discussed by Meek and Hil- 
debrand (1913), Eigenmann & Fischer 
(1914), Martin (1972), Miller & Carr 
(1974), Villa (1982), and Bussing (1987). 
Eigenmann & Allen (1942) claimed a range 
from Costa Rica to the Rio de la Plata. The 
northernmost record of a South American 
species of Gymnotus, as recognized here, is 
G. cf. anguillaris from Almirante on the At- 
lantic slope of Panama (Behre 1928, Hil- 
debrand 1938, see Appendix), located about 
170 km south of the southern limit of G. 
cylindricus at Tortuguero, Sixaloa, Costa 
Rica (Gilbert & Kelso 1971). The northern 
limit of G. carapo on the pacific slope is 
from Pizarro, Choco, Colombia. No refer- 
ences were found for the presence of G. 
carapo from the Rio Tuira or elsewhere in 
Panama. 
The two species of Gymnotus limited to 
Middle America come into closest contact 
in small streams on opposite sides of Lake 
Nicaragua, and in several tributaries of the 
Rio San Juan in Northern Costa Rica, an 
Atlantic drainage. The presence of G. ma- 
culosus in these localities may have resulted 
from stream capture due to tectonic uplift 
of the region in the past several million 
years (Durham 1944; Miller 1950, 1986). 
Geologic evidence for the uplift of the Nic- 
araguan graben is discussed by Riedel 
(1972). 
The parapatric distribution of species of 
Gymnotus is similar to that of some other 
fishes in the lake Nicaragua basin. The shad 
Dorosoma chavesi, the poeciliid Poeciliop- 
sis cf. turrubarensis, and the gar Atractos- 
teus tropicus found in this basin are other- 
wise only known from Pacific-slope drain- 
ages. A second species of poeciliid record- 
ed from the Lake Nicaragua basin, P. cf. 
gracilis, also occurs on the Atlantic slope 
in southern Mexico and in the Rio Motagua 
of Guatemala. The sawfish Pristis pectina- 
ta, and the tarpon Tarpon atlanticus, both 
found in Lake Nicaragua, are confined to 
the Atlantic basin. 
Key to adults of species of Gymnotus 
(HL greater than 10 mm) 
la. No oblique bands on body; body cavity 
with 31-35 (mode = 32) precaudal ver- 
tebrae 2 
lb. Alternating bands of dark and pale pig- 
mentation arranged at an oblique angle 
along length of body; body cavity with 
36-51 precaudal vertebrae 3 
2a. Numerous small brown spots on body; 
eyes set close together, interorbital dis- 
tance 37^1% HL; scales above lateral 
line large, 6-8 rows at midbody 
Gymnotus maculosus, n. sp. 
2b. Few if any spots on body; eyes set 
apart, interorbital distance 41^6% HL; 
scales above lateral line small, 10-12 
rows at midbody 
Gymnotus cylindricus LaMonte 
3a. Body deep, depth at anal-fin origin 
more than about 9% TL (except G. 
pantherinus); alternating dark and pale 
oblique bands of equal width at mid- 
body, or pale bands broader; ground 
color dusky brown on dorsum; anal fin 
hyaline posteriorly 4 
3b. Body slender, depth at anal-fin origin 
less than about 9% TL; dark oblique 
bands broader than pale bands at mid- 
body; ground color dark brown or dark 
grey on dorsum; anal fin pigmented 
posteriorly 6 
4a. Head long, HL greater than about 1 1 % 
TL for specimens 100-250 mm TL); no 
spots on body, dark oblique bands un- 
interrupted; pigment density in middle 
part of dark bands less dense than near 
margins; bands present on anterior por- 
tion of body . . Gymnotus carapo (Linneus) 
4b. Head short, HL less than about 1 1 % 
TL; spots on head and back, dorsal part 
of dark oblique bands interrupted; dark 
oblique bands of uniform pigment den- 
sity; bands not present on anterior half 
of body in specimens larger than 220 
mm TL 5 
674 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
5a. Body deep, BD greater than 9% XL 
. Gymnotus inaequilabiatus (Valenciennes) 
5b. Body shallow, BD less than 9% TL 
.... Gymnotus pantherinus (Steindachner) 
6a. Eyes set further apart, lO 39-44% HL; 
nape dark, pale bands not extending 
above lateral line on anterior half of the 
body . . Gymnotus anguillaris Hoedeman 
6b. Eyes set closer together, TO 25-38% 
HL (except some G. cataniapo); white 
band at nape, pale bands extending to 
dorsal midUne on anterior half of body 
7 
7a. 13-23 oblique bands; pectoral fin lon- 
ger, 38-54% HL 8 
7b. 23-50 oblique bands; pectoral fin short- 
er, 28-37% HL 9 
8a. Body cavity shorter, 40^2 precaudal 
vertebrae; alternate pale bands incom- 
plete Gymnotus coatesi LaMonte 
8b. Body cavity longer, 47-48 precaudal 
vertebrae; all pale bands complete 
Gymnotus stenoleucus Mago-Leccia 
9a. Head shorter, HL 8-10% TL; body cav- 
ity shorter, 50-51 precaudal vertebrae; 
posterior end of anal fin dark 
Gymnotus cataniapo Mago-Leccia 
9b. Head longer, HL 12-14% TL; body 
cavity shorter, 36-37 precaudal verte- 
brae; posterior end of anal fin pale 
.... Gymnotus pedanopterus Mago-Leccia 
Acknowledgments 
William Bussing, David Catania, Mary 
Anne Rogers, Bill Saul, and Richard Vari 
provided many specimens used in this 
study. Sara Fink helped interpret the mor- 
phology of the ethmoid region. Tamaki Yuri 
helped with construction of the key. Ricar- 
do Campos-da-Paz and John Sullivan pro- 
vided useful comments on the characters. 
William Bussing, John Lundberg, and Rich- 
ard Vari made many useful suggestions on 
earlier drafts of the manuscript. We thank 
the Smithsonian Institution photographic 
laboratory for the photograph reproduced in 
Fig. 1, and Margaret Van Bolt who re- 
touched the background. Brian Dyer pro- 
vided the Spanish abstract. We acknowl- 
edge the NEODAT project (NSF/AID DEB 
grant 90-24797) for collection information. 
We thank Doug Nelson for curatorial assis- 
tance, and the Secretaria, Departamento de 
Pesca, for permission to collect in Mexico. 
Part of the research reported was conducted 
in facilities provided by NSF grant BSR 
9015158 to Willim Fink. 
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Appendix 1 
List of 125 lots containing 698 specimens of gym- 
notids examined. Data are arranged by country, then 
alphabetically by museum acronym and number. Cat- 
alogue numbers are followed in parentheses by number 
of specimens, and then by locality, size range in mil- 
limeters total length (mm), and date of capture. 
Gymnotus anguillaris. — Guyana: FAU uncat. (2), 
Madewini River, 132-165 mm, 1994.IV.20. Paraguay: 
UMMZ 206080 (21), Arroyo in Parque Nacional Yby- 
cui, 82-260 mm, 1979.VI.20. Suriname: UMMZ 
190413 (6), Maka Creek, Lawa River, Morowyne, 
1967.IV21. ZMA 100338 (2), Coropina Creek, 228- 
236 mm, 1956.V.20. 
Gymnotus cf. anguillaris. — Panama: CAS 72209 
(2), small creek into Rio Cricamola, behind Konkintu, 
Boca del Toro Province, 225-239 mm, 1923.11.25. 
Gymnotus carapo. — Bolivia: UMMZ 066433 (2), 
Lake Rogoagua, Rio Beni, 214-338 mm, 1921. IX. 
UMMZ 066462 (2), Reyes, Rio Beni, 205-245 mm, 
1921. IX. UMMZ 204299 (1), Costa Marquez, Rio It- 
enez (Guapore), Madeira, 164 mm, 1964. IX. 02. 
UMMZ 204771 (5), Costa Marquez, Rio Itenez, 44- 
51 mm, 1 964.x. 1. UMMZ 204886 (3), Rio Baures, 
Rio Itenez, 145-345 mm, 1964.X.7. Brazil: UMMZ 
143282 (2), Lagoa dos Quadros, Rio Grande do Sul, 
Tramandai, 55-129 mm, 1941. VIII. UMMZ 230732 
(2), Aggassiz collections, presumably Brazil, 174-202 
mm. Ace. 1876.V.9. UMMZ 230734 (2), Rio Cayari 
near Benjamin Constant, Amazonas, 190-210 mm, 
1993.V.11. USNM 199215 (1), Upper Yuruena, Mato 
Grosso, 85 mm, 1964.VII.20. USNM 199219 (2), Up- 
per Yuruena, Mato Grosso, 1965.IV.9. Colombia: CAS 
072192 (2), Rio Sucio, Rio Truando, Rio Atrato, 150- 
179 mm, 1913. FMNH 56793 (2), mouth of Rio Cal- 
ima, Rio Atrato, 1913. FMNH 56794 (2), Rio Sucio, 
Rio Truando, Rio Atrato, 174-175 mm, 1913. FMNH 
70511 (5), Pizarro, Choco, Pacific drainage, 124-247 
mm, 1945. IX. Peru: UMMZ 072636 (2), Yurimaguas, 
Rio Maranon, 148-214 mm, 1920.IX. UMMZ 230733 
(1), Quebrada near Buen Sucesso, Rio Javari, Loreto, 
250 mm, 1993.V.15. UMMZ 228998 (2), Rio Momon, 
near Iquitos, Rio Nanay, Loreto, 38-172 mm, 
1993.V.5. UMMZ 228999 (1), Rio Tapira, Rio Tahu- 
ayo, Loreto, 161 mm, 1993.V.7. Suriname: UMMZ 
187499 (1), Brokopondo, 195 mm, 1966.IX.15. 
UMMZ 190414 (6), Brokopondo, 71-225 mm, 
1966.IX.15. ZMA 100409 (1), Aloike, Litany River, 
71 mm, 1957.XI.27. ZMA 100430 (1), He de Cayenne, 
305 mm, 1957.X.6. ZMA 100434 (2), Degrad Cacao, 
190-255 mm, 1957. XI. 10. ZMA 100439 (1), 256 mm, 
1957.X.5. Trinidad: UMMZ 169080 (2), Gunupia, Mt. 
Plaisance, 46-74 mm, 1953.III.12. Venezuela: UMMZ 
212345 (1), Esteros de Camaguan, Guarico, Apure, 45 
mm, 1981.VIII. UMMZ 214766 (1), Cano Falcon, Por- 
tuguesa, 241 mm, 1987.11.19. 
Gymnotus cataniapo. — Venezuela: MBUCV-V- 
14154 (3), cano near Salto Nieve, Rio Orinoco, 75- 
194 mm, 1983.XII.22. MBUCV-V-14300 (1), Cano 
Merete, Rio Casiquiare, 213 mm, 1984. VIII. 20. 
MBUCV-V- 14736 (1), San Carlos de Rio Negro, Rio 
Orinoco, 253 mm, 1984.X.4. MCUCV-V- 14757 (1), 
Caiio Guayabal, near Puerto Ayacuchu, Rio Orinoco, 
114 mm, 1984.XII.12. MBUCV-V-14781 (15), Cano 
Las Pevas, Rio Casiquiare, 143-316 mm, 1984.VIII.2. 
VOLUME 108, NUMBER 4 
677 
Gymnotus coatesi. — Bolivia: UMMZ 205149 (7), 
near Guayaramerin, Arroyo Grande, 45-175 mm, 
1964.X.23. Paraguay: UMMZ 206155 (2), near San 
Rafael, Arroyo Tembley, 194-225 mm, 1979.VI.26. 
Peni: UMMZ 224596 (10), Buen Sucesso, Rio Javari, 
Loreto, 45-167 mm, 1993. V. 15. UMMZ 224599 (2), 
Quebrada near Buen Sucesso, Rio Javari, Loreto, 
1993. V. 15. UMMZ 224601 (1), cafio near Santa Ana, 
Rio Tahwayo, Loreto, 1993.V.4. UMMZ 224607 (6), 
near Iquitos, Rio Nanay, 30-144 mm, 1993.V.4. 
Gymnotus cylindricus. — Costa Rica: UCR 1014-1 
(12), Rio Escondido, Limon, Rio Sixaola, 123-249 
mm, 1976.IX..17. UCR 280-2 (3), Rio Escondido, Li- 
mon, Rio Sixaola, 1968.X.3. UMMZ 224129 (10), Rio 
Escondido, Limon, Rio Sixaola, 131-205 mm, 
1968.X.3. Guatemala: UMMZ 193873 (2), el Progres- 
so, Morazan, Rio Yeguare, 192-210 mm, 1973.III.24. 
UMMZ 193986 (14), Quebrada de Vegega, Los 
Amates, Rio Izabal, 26-183 mm, 1973.IV.5. Honduras: 
UMMZ 155831 (1), bridge on Tegucigalpa-Danli road, 
Rio Yeguare, 174 mm, 1948.1.30. UMMZ 155832 (2), 
Quebrada near Los Flores, Rio Yeguare, 161-204 mm, 
1947.Vn.23. UMMZ 188110 (2), Pito Solo, Cortez, 
Rio Jaitique, 93-191 mm, 1948.V.23. UMMZ 188273 
(1), Lago Yoyoa, Santa Barbara, Rio Yeguare, 135 
mm, 1949.Vra.l. UMMZ 188274 (5), Lago Yojoa, 
Santa Barbara, Rio Yeguare, 97-175 mm, 1948.IV. 14. 
UMMZ 188275 (16), Lago Yojoa, Rio Yeguare, 166- 
224 mm, 1949.Vm.lO. UMMZ 188296 (2), Quebrada 
Lagunita, Morazan, Rio Yeguare, 120-138 mm, 
1947.VII.29. UMMZ 188297 (5) Quebrada behind fin- 
ca de Rudolfo Rosales, Rio Yeguare, 69-129 mm, 
1947.XL UMMZ 199598 (1), Laguna Sikalanka, Rio 
Sucre, 215 mm, 1975.V.11. Nicaragua: CAS 161383 
(3), Rio Frio, about 1.5 mi. above San Carlos, in bayou 
with sluggish current, Lago Nicuaragua drainage, Rio 
San Juan state, 1963.n.l2. TU uncat. (1), San Carlos, 
Lago Nicuaragua drainage, Rio San Juan state. UMMZ 
199622 (13), SE of Bilwaskarma, Rio Kurnog, 
1975.V.13. UMMZ 199633 (2), Rio Putkrukira near 
Waspan, Rio Coco, 121-194 mm, 1975.V.27. 
Gymnotus inaequilabeatus. — Brazil: USNM 1643 
(1), Rio Paraguay, 791 mm. USNM 1644 (1), Rio Par- 
aguay. USNM 1645 (1), Rio Paraguay. Paraguay: 
UMMZ 206939 (1), near Pto. Stroessner, Arroyo Ve- 
necia, 154 mm, 1979.Vin.5. UMMZ 206703 (4), Pe- 
dro Juan Caballero, Parana, 113-280 mm, 1979.VI.24. 
UMMZ 206971 (2), Estancia la Golondrina, Presidente 
Hayes, Confuso, 255-261 mm, 1979. VIII. UMMZ 
207025 (17), marsh 34 km N.W. Pt. Remaro bridge, 
Rio Confuso, 485 mm, 1979.VIII.9. UMMZ 207096 
(3), Estancia la Golondrina, Presidente Hayes, Confu- 
so, 132-210 mm, 1979. VIII. UMMZ 207564 (2), Rio 
Pilcomayo near Peurto Falcon, Rio Paraguay, 220-242 
mm, 1979.VIII.29. UMMZ 207619 (1), Riachiielo Pil- 
co, Presidente Hayes, 144 mm, 1979.VIII.31. UMMZ 
207760 (2), Arroyo Peguajho, Ypane, 77 mm, 
1979.IX.04. UMMZ 207893 (6), Rio Aequidaban near 
Paso Hasqueta, Rio Parana, 16-390 mm, 
1979.IX.6.UMMZ 215183 (1), Estancia la Golondrina, 
Presidente Hayes, Confuso, 170 mm, 1981.X.02. 
UMMZ 216576 (1), Estancia la Golondrina, Presidente 
Hayes, Rio Confuso, 322 mm, 1981.X.02. UMMZ 
216576 (1), near Trans Chaco- Villa, Presedente Hayes, 
322 mm, 1981.X.2. 
Gymnotus maculosus. — Costa Rica: TU 24935 (16), 
La Virgin, Rio Sarapiqui, 1960.11.22. TU 25063 (3), 
Rio Tempisque, near Liberia, Guanacaste, 193-218 
mm, 1961.1.21. UCR 969-9 (20), Santa Cruz, Rio Gar- 
zon, Guanacaste, 123-195 mm, 1976.1.25. UCR 980- 
9 (5), Arenal, Rio Dos Bocas, Guanacaste, Rio San 
Carlos drainage, 1968.VI.10. UMMZ 158451 (1), Fin- 
ca la Trinidad, Guanacaste, 179 mm, 1949.X.21. 
UMMZ 224128 (5), Rio Higueron, near Canas, Guan- 
acaste, 158-222 mm, 1968. VI. 10. Guatemala: UMMZ 
188072 (1), Rio Bravo, Rio Nahualate, 1968.IV.3. 
UMMZ 190531 (7), El Obraje, Jutiapa, Rio Grande de 
Pasaco, 146-200 mm, 1971.III.9. UMMZ 190783 (3, 
paratypes), diversion of channel from Rio Maria Lin- 
da, 20 km East of Escuintla, Departamento Santa Rosa, 
176-203 mm, 1971.III.27. UMMZ 194122 (6), 2.6 km 
ESE Eca Cocales, Rio La Primavera, 105-135 mm, 
1973.IV.20. UMMZ 194150 (2), Rio Siguacan, near 
Escuintla, Santa Rosa, 141-172 mm, 1973.IV.24. 
UMMZ 197103 (17), near Taxisco, Santa Rosa, 
1974.IV26. UMMZ 197103 (20), Taxisco, Santa Rosa, 
78-227 mm, 1974.IV.6. UMMZ 230354 (20, para- 
types), Rio Buena Vista, trib. of Rio Tigre, on road 
between Escuintla and Chiquimulilla, 8 km West of 
Pajal, Departamento Santa Rosa, Guatemala, 128-230 
mm, 1946.IV. 18. UMMZ 230830, (1, holotype), diver- 
sion of channel from Rio Maria Linda, 20 km East of 
Escuintla, Departamento Santa Rosa, 191 mm, 
1971.III.27. USNM 114235 (2), Rio Colojate, 1947. 
USNM 114539 (22), near Malacatan, Rio Gramal, 
1956.VII.6. USNM 134700 (49, paratypes), near Pajal, 
Rio Buen Vista, 138-226 mm, 1946.IV. 18. USNM 
225435 (1), Rio Chiquimulilla, 1946. USNM uncat. 
Rio Hondo, 1946. USNM uncat. (8), Rio Lato, 1946. 
USNM uncat. (23), Rio Grammal, 1947. Mexico: 
UMMZ 191702 (2), Tapachula, Rio San Nicolas, Chia- 
pas, 163-189 mm, 1971.in.l3. UMMZ 191712 (3), 
Tapachula, Rio San Nicolas, Chiapas, 184-228, 
1971.11.27. Nicaragua: TU 24965 (38, paratypes), 
Boca de Rio Sapoa, Sapoa, Lago Nicaragua drainage, 
Rivas Province, 1960.IV.23. TU 25032 (1), Boca de 
Rio Sapoa, Sapoa, Lago Nicaragua drainage, Rivas 
Province, 43 mm, 1961.1.21. 
Gymnotus n. sp. N. — Ecuador: FMNH uncat. (46), 
Aguarico, Rio Napo, 1983.XI.21. 
Gymnotus pantherinus. — Brazil: USMN 297933 
(20), Naneia, Sao Paulo, 1988.ii.21. USMN 297939 
(12), Guaratuba, Rio da Praia, 1988.X.3. 
Gymnotus pedanopterus. — Venezuela: MBUCV-V- 
14737 (2), Cafio Chola, near San Carlos de Rfo Negro, 
Rfo Casiquiare, 198-228 mm, 1984.XI. MBUCV-V- 
678 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
14738 (1), Cano Temblador, Rio Casiquiare, 215 mm, 
1984.XII.5. MBUCV-V-4860 (1), Cano Esmeralda, 
Rio Orinoco, 281 mm, 1966.XI.6. MBUCV-V-7135 
(2), El Pozo de Lucas, near San Fernando de Atabapo, 
Rio Orinoco, 109-119 mm, 1973. MBUCV-V-7310 
(3), cano near San Fernando de Atabapo, Rio Orinoco, 
92-185 mm, 1972.IV. 14. 
Gymnotus stenoleucus. — Venezuela: MBUCV-V- 
14028 (15), Rio Cataniapo, Rio Orinoco, 80-171 mm, 
1983.III.30. MBUCV-V-14747 (1), Caiio Guayabal, 
near Peurto Ayacuchu, Rio Orinoco, 140 mm, 
1984.XII.12. MBUCV-V-4644 (2), Rio Quiritare, Rio 
Orinoco, 91-95 mm, 1966.X.30. MBUCV-V-6218 (1), 
Cano Caripo, Rio Casiquiare, 140 mm, 1969.1.26. 
MBUCV-V-9417 (4), Cano Caripo, Rio Casiquiare, 
91-142 mm, 1969.1.26. 
Electrophorus electricus. — Aquarium: UMMZ 
183710-S (1), 100 mm+, 1961.Vn.l. Bolivia: UMMZ 
204426-S (2), Costa Marques, Rio Itenez, Rio Madei- 
ra, 940 mm, 1964.IX.12. Guyana: USNM 228883 (3), 
Essequibo River. UMMZ uncat. (1), 1000+ mm, 
1992.XII.12. Suriname: USNM 225669 (1), Amotopa 
landing, Nickerie District, Rio Corantijn, 511 mm, 
1980.VII.19.