A Review of the South American Electric Fish Genus Porotergus (Gymnotiformes: Apteronotidae) with the Description of a New Species

Abstract

The species currently assigned to the South American electric fish genus Porotergus are reviewed. Porotergus duende, a new species, is described from the lowland western Amazon basin in Brazil and Peru. Porotergus gimbeli from the lowland Amazon basin in Brazil and Peru, and P. gymnotus from the Essequibo drainage of Guyana are redescribed. Porotergus duende and P. gimbeli are restricted to deep channel habitats. Porotergus gymnotus occurs in shallow rivers. Notes on the ecology and electric organ discharge of P. duende and P. gimbeli are presented. A key to the members of the genus is provided. /// As espécies de peixes elétricos Sul Americanos do gênero Porotergus são revisadas. Porotergus duende, uma nova espécie, é descrita para a porção oeste da bacia Amazônica Brasileira e Peruana. Porotergus gimbeli que ocorre nas porções leste e oeste da bacia Amazônica Brasileira e Peruana, e P. gymnotus do rio Essequibo na Guiana são redescritas. Porotergus duende e P. gimbeli habitam os canais profundos dos rios. Porotergus gymnotus ocorre em rios de águas rasas. Notas sobre a ecologia e a descarga do órgão elétrico são fornecidas para P. duende e P. gimbeli. Uma chave para as espécies do gênero é apresentada.

Full text

A Review of the South American Electric Fish Genus Porotergus
(Gymnotiformes: Apteronotidae) with the Description of a New Species
Carlos David de Santana
1
and William G. R. Crampton
2
The species currently assigned to the South American electric fish genus Porotergus are reviewed. Porotergus duende,a
new species, is described from the lowland western Amazon basin in Brazil and Peru. Porotergus gimbeli from the
lowland Amazon basin in Brazil and Peru, and P. gymnotus from the Essequibo drainage of Guyana are redescribed.
Porotergus duende and P. gimbeli are restricted to deep channel habitats. Porotergus gymnotus occurs in shallow rivers.
Notes on the ecology and electric organ discharge of P. duende and P. gimbeli are presented. A key to the members of the
genus is provided.
As espe´cies de peixes ele´tricos Sul Americanos do geˆnero Porotergus sa˜o revisadas. Porotergus duende, uma nova espe´cie, e´
descrita para a porc¸a˜o oeste da bacia Amazoˆnica Brasileira e Peruana. Porotergus gimbeli que ocorre nas porc¸o˜es leste e
oeste da bacia Amazoˆnica Brasileira e Peruana, e P. gymnotus do rio Essequibo na Guiana sa˜o redescritas. Porotergus
duende eP. gimbeli habitam os canais profundos dos rios. Porotergus gymnotus ocorre em rios de a´guas rasas. Notas sobre
a ecologia e a descarga do o´ rga˜o ele´trico sa˜o fornecidas para P. duende eP. gimbeli. Uma chave para as espe´cies do
geˆnero e´ apresentada.
ALBERT (2001) established the tribe Porotergini to
include Adontosternarchus,Porotergus, and Sternarch-
ogiton. The Porotergini is characterized by the
following eight synapomorphies (Albert, 2001:78): ‘‘pre-
maxilla gracile, lateral margin concave, anterior margin
laminar. Some or all premaxillary teeth lost without
replacement during development, adults with fewer teeth
than juveniles. Single row of dentary teeth. Mandible
shorter than deep; oral margin of dentary shorter than
length of anguloarticular. Tip of snout curved, the ventral
ethmoid foreshortened on its long axis, and deepest
posterior to its midlength. Lateral ethmoid narrow, its base
shorter than its height. Orbitosphenoid narrow, its ventral
margin as long or shorter than its dorsal margin. Ventral
margin of parasphenoid flexed sharply on either side of
basicranial region.’’ Adontosternarchus and Sternarchogiton are
both considered monophyletic (Mago-Leccia et al., 1985;
Albert, 2001; de Santana and Crampton, 2007). Conversely,
cladistic analyses were unable to recover unambiguous
characters supporting the monophyletic condition of Por-
otergus (Albert and Campos-da-Paz, 1998; Albert, 2001;
Triques, 2005).
Ellis (in Eigenmann, 1912) established Porotergus to
include P. gymnotus from the Essequibo River in Guyana
and P. gimbeli from the Guyana and lower Amazon in the
state of Para´, Brazil. The genus was diagnosed by the absence
of scales on the dorsal region of the body anterior to the
dorsal mid-sagittal electroreceptive filament, the presence of
large scales above the lateral line, the presence of teeth in
both jaws, and the long mouth cleft reaching or passing the
vertical through the anterior margin of the eye. Based on the
characters proposed by Ellis, Ara´mburu (1957) described
P. ellisi from the lower reaches of the Rı´o Parana´in
Argentina. Mago-Leccia (1994) provided additional putative
characters for Porotergus and described P. compsus from the
Rı´o Orinoco, Venezuela. Albert (2001), however, placed
P. ellisi within Apteronotus incertae sedis,andshifted
P. compsus to the newly proposed genus Compsaraia,
retaining only P. gimbeli and P. gymnotus in Porotergus
(Albert, 2003).
A formal revision and phylogenetic analysis of Porotergus
is currently impossible, primarily because only eight
specimens of P. gymnotus are currently known from museum
collections, with none available for clearing and staining.
Nonetheless, we review the species currently assigned to the
genus and provide much needed redescriptions of P. gimbeli
and P. gymnotus. We also describe a species of Porotergus from
the western portion of the Amazon basin that is assigned to
the genus in that it does not fall within Adontosternarchus or
Sternarchogiton as those genera are presently defined.
MATERIALS AND METHODS
Body sizes were presented as total length. Measurements were
taken as point-to-point linear distances using a digital caliper
(with a precision of 0.1 mm) as follows: anal-fin base—
distance between the bases of the first and last rays of the anal
fin; branchial opening—height of the opening measured
along the vertical distance; eye diameter—horizontal width
of the eye; greatest body depth—greatest vertical extent of the
body; head depth at eye—distance measured at the center of
the eye; head length—distance from the tip of the snout to
the posterodorsal angle of the branchial opening; head
width—distance measured at the opercular region; internarial
distance—distance between the posterior of the base of the
tubular anterior naris and the anterior margin of the opening
of the posterior naris; interocular width—minimum width
between the dorsal margins of the orbits; length to end of
anal-fin (LEA)—distance from the tip of the snout to the end
of the base of the anal fin; mouth length—distance from the
tip of the snout to the rictus of the mouth; pectoral-fin
length—distance between the base of the dorsal-most ray of
the pectoral fin and the distal-most point on the margin of
the fin; posterior naris to eye—distance from the posterior
1
Department of Biology, University of Central Florida, Orlando, Florida 32816-2368; Research Collaborator, Division of Fishes, Department
of Vertebrate Zoology, MCR-159, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013-7012. Present
address: Instituto Nacional de Pesquisas da Amazoˆ nia, Av. Andre´ Arau´ jo, 2936 Manaus, AM, Brazil; E-mail: apteronotidae@ig.com.br. Send
reprint requests to this address.
2
Department of Biology, University of Central Florida, Orlando, Florida 32816-2368.
Submitted: 15 June 2005. Accepted: 28 October 2009. Associate Editor: C. J. Ferraris.
F2010 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CI-05-136
Copeia 2010, No. 1, 165–175

border of the naris to the anterior margin of the eye; posterior
naris to snout—distance from the anterior border of the naris
to the tip of snout; postocular distance—distance from the
posterior margin of the eye to the posterodorsal angle of the
branchial opening; preanal-fin distance—distance from the
tip of the snout to the base of the first anal-fin ray;
prepectoral-fin distance—distance from the tip of the snout
to the base of the dorsal-most pectoral-fin ray; snout to
anus—distance from the tip of the snout to the anterior
margin of the anus; snout length—distance from the tip of
the snout to the anterior margin of the eye; tail depth—depth
of the tail measured immediately posterior to the base of the
last anal-fin ray; tail length (CL)—distance from the base of
the posterior-most ray of the anal fin to the posterior-most
point on the body; and total length (TL)—distance from the
tip of the snout to the end of the caudal fin.
Specimens were cleared and double stained following
Taylor and Van Dyke (1985). The neurocranium, suspensor-
ium, and pectoral girdle were removed from all specimens
using standard methods for the dissection of small teleosts
(Weitzman, 1974). Osteological observations for P. gymnotus
were taken from radiographs because of the unavailability of
specimens for clearing and staining (CS). Anal fin and
vertebra counts were taken from radiographs. In the listing
of specimens, data are arranged alphabetically by species,
country, museum acronym and number, followed by number
of specimens, type status (when pertinent), and size range of
TL in mm (in parentheses). Institutional abbreviations are as
listed at http://www.asih.org/codons.pdf.
Sex was assessed by dissection. The testes of mature males
are white and smooth, whereas the ovaries of mature
females are packed with yellow or cream-colored eggs.
Immature specimens exhibit under-developed or undiffer-
entiated gonads. Sex was determined only for mature
specimens to eliminate the possibility of error. Dietary
preferences were determined by the visual analysis of
stomach contents placed in a glass dish under a stereomi-
croscope. Water quality parameters were measured follow-
ing Crampton et al. (2005). Electric signal recording
procedures follow Crampton et al. (2005).
RESULTS
Porotergus duende, new species
Figure 1, Table 1
Porotergus gymnotus.—Crampton, 1998:817 [Amazon basin;
in listing of species].
Porotergus n. sp. A.—Crampton and Albert, 2006:692
[electric organ discharges].—Crampton, 2007:298 [Ama-
zon basin; in listing of species].
Holotype.—MCP 37357, female (104), Brazil, Amazonas, Rio
Solimo˜es, beach on north bank of Ilha Cuera, near Tefe´,
Municipality of Alvara˜es, 3u21.219S, 64u39.599W, 27 January
2001, W. Crampton.
Paratypes.—All from Amazonas, Brazil: INPA 25257, 1, male
(CS; 82.4), collected with holotype. INPA 24567, 2, imma-
ture (58.5–64), Rio Madeira. MCP 37359, 1, male (69.1), Rio
Solimo˜es, beach on north bank of Ilha do Ic¸e´, near Tefe´,
3u13.119S, 64u43.119W, 30 January 2001. MCP 37360, 1,
female (84.4), Rio Solimo˜es confluence with Rio Japura´,
beach in front of village of Caborini, 3u09.149S, 64u47.069W,
12 February 2001 (all MCP specimens collected by second
author). MZUSP 56209, 6 (66–184), Rio Negro, 12 km below
Rio Jufari. MZUSP 56542, 5 (66–107), Rio Amazonas, near
Rio Madeira, 8 August 1996, M. Toledo-Piza. MZUSP 56544,
2 (134–139), Rio Solimo˜es, below Rio Purus, 3u36.259S,
61u18.549W, 28 July 1996. MZUSP 56545, 8 (56–125), Rio
Solimo˜es, near Rio Purus, 3u35.579S, 61u7.539W, 31 July
1996. MZUSP 57274, 1 (58), Rio Solimo˜es, below Rio Purus,
31 July 1996, A. M. Zanata et al. MZUSP 57343, 1 (64), Rio
Solimo˜es, above Rio Purus. MZUSP 57354, 3 (75–115), Rio
Solimo˜es, above Vila do Careiro, 21 July 1996, A. M. Zanata
et al. MZUSP 57975, 1 (79); MZUSP 57976, 1 (94), Rio
Amazonas, 11 miles below Rio Negro, 22 July 1996, C. Cox-
Fernandes et al.
Non-type specimens.—Peru: UF 129817, 2, immature (87–90),
Loreto, Rı´o Ucayali, beach on Can˜o Puinahua, 4 km
upstream of mouth of Rı´o Pacaya.
Diagnosis.—Porotergus duende is diagnosed from all conge-
ners by the presence of a light brown body pigmentation
(versus pale straw pigmentation in P. gimbeli, and dark
brown in P. gymnotus), the one row of conical teeth on the
dentary (versus two rows), the edentulous premaxilla (versus
presence of teeth), and the ossified second basibranchial
(versus unossified in P. gimbeli, condition unknown in P.
gymnotus). It is further diagnosed from P. gimbeli by the
absence of a distinct swelling on the chin (versus presence of
this structure), the total anal-fin rays (124–142 versus 171–
198), and the prepectoral-fin distance (14.1–17.0%of LEA
versus 10.3–13.5). It is diagnosed from P. gymnotus by the
distance from the posterior naris to the eye (1.7–3.8%of HL
versus 8.2–11.9), the mouth length (12.4–27.4%of HL
versus 28.1–38.7), and the pectoral-fin length (72.7–89.0%
of HL versus 60.4–70.7).
Description.—Head and body shape and pigmentation
illustrated in Figure 1. Maximum examined body size
Fig. 1. Head (live) and body (recently preserved) of Porotergus duende
holotype, MCP 37357, 104.0 mm. Scale bars 510 mm. Dorsal mid-
saggital electroreceptive structure partially dislodged, as often occurs in
preserved specimens but never in live fish.
166 Copeia 2010, No. 1

Table 1. Morphometric Data for Three Species of Porotergus. Number of specimens indicated in parentheses. Ranges include all specimens.
Holotype
P. duende P. gimbeli P. gymnotus
Range Mean Holotype Range Mean Holotype Range Mean
Total length (mm) 104.0 69.0–140.0 (n58) – 200.0 106.6–270.0 (n541) – 65.2 65.2–113.0 (n55) –
Length to end of anal fin (mm) 94.0 64.0–115.0 (n58) – 170.0 91.7–173.0 (n521) – 53.8 53.8–98 (n55) –
Head length (mm) 11.4 9.2–15.4 (n58) – 20.4 11.7–25.1 (n541) – 8.6 8.6–16.3 (n55) –
Tail length (mm) 9.5 9.2–24.0 (n57) – 25.4 10.9–25.4 (n510) – 10.9 10.0–17.0 (n55) –
Percent of length to end of anal fin
Anal-fin base 96.8 81.1–96.8 (n58) 88.2 91.5 86.2–93.7 (n521) 90.3 83.1 81.6–83.6 (n55) 82.7
Snout to anus 6.5 6.1–9.2 (n58) 7.8 5.0 4.5–7.8 (n521) 5.8 10.2 6.3–10.4 (n54) 8.6
Preanal-fin distance 12.3 11.8–14.7 (n58) 13.2 9.8 7.3–13.7 (n521) 9.9 16.2 12.9–19.0 (n55) 15.5
Prepectoral-fin distance 14.1 14.1–17.0 (n58) 15.2 12.1 10.3–13.5 (n521) 12.3 16.8 16.8–18.0 (n54) 17.5
Greatest body depth 16.1 13.5–16.7 (n58) 15.2 11.8 10.8–14.4 (n521) 12.6 16.0 13.8–16.0 (n55) 14.0
Tail length 10.2 10.1–24.1 (n57) 18.1 14.9 9.2–15.7 (n510) 14.0 20.3 13.1–20.3 (n55) 17.1
Head length 12.2 12.2–15.3 (n58) 13.8 12.0 10.0–13.0 (n521) 11.9 16.0 13.8–16.6 (n55) 15.3
Percent of head length
Pectoral-fin length 85.4 72.7–89.0 (n58) 81.8 68.6 66.2–92.7 (n541) 79.5 69.4 60.4–70.7 (n55) 66.1
Head depth at eye 67.1 49.2–70.5 (n58) 58.6 61.4 28.0–64.7 (n541) 54.4 60.1 46.0–60.1(n55) 52.2
Head width 57.8 51.9–58.5 (n58) 54.7 40.8 40.8–53.5 (n541) 47.8 43.4 30.1–55.9 (n55) 45.3
Snout length 31.5 25.7–31.8 (n58) 30.1 25.6 23.2–29.1 (n541) 26.1 31.5 31.5–36.3 (n55) 35.3
Posterior naris to snout 20.1 20.1–27.1 (n58) 23.5 16.9 13.8–20.0 (n540) 16.9 23.6 23.6–31.7 (n54) 27.4
Posterior naris to eye 3.4 1.7–3.8 (n58) 2.9 5.6 2.2–10.7 (n541) 6.2 5.2 8.2–11.9 (n54) 9.7
Mouth length 23.4 12.4–27.4 (n58) 18.6 34.0 23.1–36.8 (n541) 30.4 29.5 28.1–38.7 (n54) 34.6
Internarial distance 8.9 8.1–14.7 (n58) 11.0 7.9 5.8–11.1 (n541) 8.8 10.3 10.3–15.0 (n54) 13.7
Eye diameter 10.5 7.2–10.5 (n58) 8.5 7.2 7.1–10.4 (n541) 8.8 8.2 7.5–10.3 (n55) 8.8
Interocular width 39.8 28.2–39.8 (n58) 31.5 22.5 19.3–28.7 (n540) 23.2 29.8 22.3–29.8 (n55) 26.2
Postocular distance 78.5 63.6–78.5 (n58) 67.4 65.3 61.0–74.3 (n540) 66.4 64.5 59.5–69.0 (n55) 64.0
Branchial opening 27.6 15.1–27.6 (n58) 19.6 18.7 16.1–25.9 (n540) 21.4 22.7 14.4–33.3 (n53) 22.6
Percent of caudal length
Tail depth 12.3 6.3–19.6 (n57) 12.2 17.7 18.2–22.7 (n59) 19.9 7.9 6.8–12.9 (n55) 9.8
de Santana and Crampton—Review of Porotergus 167

140 mm. Morphometric data presented in Table 1. Body
laterally compressed. Greatest body depth at abdominal
cavity, or slightly posterior. Dorsal profile of body nearly
straight. Lateral line extending posteriorly to a position 10
to 12 scales anterior to base of caudal fin, but absent on fin.
Anterior-most perforated scale located above pectoral-fin
origin. Head laterally compressed, widest at opercular
region, deepest at nape. Dorsal profile of head very convex.
Eye small, located laterally on head and completely covered
by thin membrane.
Upper and lower jaws equal. Mouth terminal. Rictus
located at vertical through anterior margin of eye. Anterior
naris located at end of small tube, and close to tip of snout.
Posterior naris ovoid, without tubular extension and closer to
eye than to tip of snout. Branchial opening located slightly
anterior to pectoral-fin origin. Branchial membranes joined
at isthmus. Anus and urogenital papilla adjacent located at
vertical approximately one orbital diameter posterior to eye,
and without noticeable forward displacement ontogenetical-
ly. Premaxilla of moderate size, edentulous. Dentary with one
tooth row, with seven conical functional teeth and one
replacement tooth. First and second basibranchials ossified.
Posterior basibranchials cartilaginous.
Pectoral fin broad and distally pointed, with 12–16 [16] (n
59) rays. Anal-fin origin located anterior to vertical through
posterior margin of opercle. Total anal-fin rays 124–142
[141] (n58). Scales absent along entire middorsal region of
body. Scales above lateral line to middorsal line 5–7 [7] (n5
8). Dorsal mid-sagittal electroreceptive filament inserted
into narrow mid-dorsal groove. Origin of filament located at
50%of TL. Filament extending posteriorly to vertical
through rear of base of anal fin. Tail compressed and long,
ending in small, lanceolate caudal fin. Caudal-fin rays 14–15
[15] (n56). Caudal fin frequently missing or partially
regenerated. Precaudal vertebrae 15–17 [15] (12 anterior, 3
transitional, n54).
Secondary sexual dimorphism.—No sexual dimorphism of the
cranial or post-cranial morphology or of the pigmentation
was observed in mature specimens.
Coloration in life.—Ground color of body uniformly pale tan
to gray, darker dorsally with brown middorsal region. Flanks
and anal-fin pterygiophores lightly scattered with dark
brown chromatophores. Dark chromatophores combine
dorsally to produce brown ground color. Tuberous electro-
receptors clearly visible as small pale pits uniformly
distributed along body, and with increased density on head
and dorsal mid-saggital organ. Anal and pectoral fins
hyaline. Caudal-fin membranes hyaline, and light scattering
of brown chromatophores over fin rays. Chromatophore
density on caudal fin increases proximally to produce
indistinct dark patch at base. Pale band almost free of dark
chromatophores extending around caudal peduncle located
immediately anterior to caudal-fin base. Width of band
equal to about one-half caudal-fin length.
Coloration in alcohol.—Much as in life, but with darker
pigmentation less intense. Body coloration light brown. Pale
band encircling base of caudal fin.
Electric organ discharges.—Crampton and Albert (2006)
report P. duende to generate a continuous wave (tone)-type
electric organ discharge (EOD) with a fundamental frequen-
cy (cycle rate) of 1393–1428 Hz (mean 1405, SD 19.7, n53).
The EOD waveform (reported for a single mature male, MCP
37360) contains four phases of alternating polarity corre-
sponding to a type-F category of apteronotid EOD (sensu
Crampton and Albert, 2006), with the peak power frequency
corresponding to the second harmonic. Sexual differences in
EOD discharge rate were not observed (female 1394 Hz, n5
1; male 1396–1429 Hz, n52). No spontaneous amplitude
modulations (chirps) or other EOD modulations (Turner et
al., 2007) were observed.
Ecology.—Porotergus duende is known mainly from the main
channels of large whitewater rivers such as the Rio Solimo˜es
(Amazon) and Rı´o Ucayali. In the Tefe´ region, this species
was encountered only during the rising water period in
January and February, and was captured in waters of 2–4 m
depth on beaches of alluvial silt and fine sand. The Rio
Solimo˜ es near Tefe´ is characterized by high conductivity (90–
150 mScm
21
), very high turbidity (Secchi disk readings of 0.1–
0.4 m, but usually less than 0.15 m), near neutral pH
(pH 6.9–7.3), and is well oxygenated from the surface to the
bottom (1.6–3.9 mg/l, usually more than 3 mg/l). The
temperature of large whitewater rivers is remarkably constant
throughout the year (27–32uC), with no stratification. Water
chemistry readings at the capture locality of two specimens
from the lower Rı´o Ucayali (UF 129817) fell within the above
ranges. All four specimens captured in the Tefe´ region (MCP
37357–37360) had maturing, but not fully mature, gonads.
This suggests spawning during the rising water period, which
is typical of riverine apteronotids (Crampton, 1998). Stomach
content analysis was based on four specimens from the Tefe´
region. This species feeds exclusively on small, autochtho-
nous, benthic insect larvae. Micro-caddis fly larvae (Trichop-
tera: Hydroptilidae) constituted 80–100%(mean 87.5, SD 9.6,
n54), biting midge larvae (Diptera: Ceratopogonidae)
constituted 0–20%(mean 7.5, SD 9.6, n54), and beetle
larvae (Coleoptera of unidentifiable families) constituted 0–
20%(mean 5, SD 10, n54) of proportional contents. Most
specimens had loose sand grains in the stomach (larger than
the grains of sand in the caddis fly jackets), suggesting
foraging on sandy substrates. One stomach contained many
endoparasitic nematodes.
Distribution.—Porotergus duende is known from the main
channel of the Amazon River in the western portions of the
Amazon basin (Rio Negro and Rio Solimo˜es in Brazil, Rı´o
Ucayali in Peru; Fig. 2).
Fig. 2. Geographic distribution of Porotergus duende (squares; 1 5
type locality at Amazon River, near city of Tefe´). Some symbols
represent more than one lot or locality.
168 Copeia 2010, No. 1

Etymology.—The specific epithet, duende, is the Portuguese
for elf or imp, referring to the diminutive size of P. duende.A
noun in apposition. Gender masculine.
Remarks.—The Peruvian lot is excluded from the type series
due to the geographical distance separating it from the
Brazilian lots. However, the Peruvian specimens unques-
tionably belong to the same species and exhibit identical
morphology.
Porotergus gimbeli Ellis, 1912
Figures 3, 4; Table 1
Porotergus gimbeli.—Ellis in Eigenmann, 1912:441 [type
locality: Para´ , Brazil].–Ellis 1913:154, pl. 23, fig. 3 [lower
Amazon basin and Guyana; first illustration].–Henn,
1928:70 [in listing of type species].–Ortega and Vari,
1986:12 [Peru].–Ibarra and Stewart, 1987:69 [in listing of
type species].–Mago-Leccia, 1994:33, 148, fig. 43 [in
listing of members of genus; illustration of FMNH 54567
from Para´, Brazil (mistakenly reported to be from Guyana
in figure legend)].–Crampton, 1998:817 [Amazon basin;
in listing of species].–Albert and Campos-da-Paz,
1998:433 [in listing of members of genus].–Cox-Fer-
nandes, 1999:28 [Amazon basin, in species list].–Albert,
2001:78, 91 [Amazon basin; in listing of members of
genus].–Albert, 2003:500 [Brazil; in listing of members of
genus].–Cox-Fernandes et al., 2004:unpaginated [elec-
tronic supplement; Amazon basin; in listing of species].–
Triques, 2005:140 [phylogenetic relationships; autapo-
morphies].–Crampton and Albert, 2006:691 [electric
organ discharge].–Crampton, 2007 [Amazon basin; in
listing of species].–Triques, 2007:124 [in listing of species
in Brazil].
Material examined.—Brazil. Amazonas: FMNH 115064, 266,
Rio Japura´ , between Serraria and Porto Caborira. FMNH
115065, 3, Rio Solimo˜es, between Parana´ Amatura and Rio
Ic¸a´, between Rural Muiraquita and Sa˜o Antoˆnio do Ic¸a´.
FMNH 115066, 20; FMNH 115067, 15, Rio Solimo˜es,
between Rio Ic¸a´ and Rio Tonantins, between Sa˜o Antoˆ nio
do Ic¸a´ and Nova Tonantins. FMNH 115068, 5, Rio Solimo˜es,
between Parana´ das Flores and Lago Anori, between Codajas
and Anori. FMNH 115069, 1, Rio Solimo˜es, between Rio
Jurua´ and Parana´ do Macuapanim, between Tamanicoa and
Palheta. FMNH 115070, 2, Rio Jurua´, between Lago Pauapix-
una and Solimo˜es, between Pauapixuna and Tamanicoa.
FMNH 115071, 4, Rio Solimo˜es, between Rio Japura´ and
Lago Caiambe´ , between Alvara˜es and Caiambe´ . FMNH
115072, 4, Rio Jurua´, between Lago Pauapixuna and Lago
Meneroa, between Pauapixuna and Tamanicoa. FMNH
115073, 4, Rio Solimo˜ es, between Rio Jutaı´ and Parana´do
Inferno, between Foz do Jutaı´ and Ponta Grossa. FMNH
115074, 30, Rio Japura´, between Parana´ do Jaraua´ and Rio
Solimo˜es, between Nova Betaˆnia and Serraria. FMNH
115075, 3, Rio Amazonas, between Rio Parana´ da Eva and
Rio Madeira, between Santo Antoˆnio and Santa Maria.
FMNH 115079, 2, Rio Madeira, between Parana´ do Maraca´
and Parana´ Ipiranga, between Nova Olinda do Norte and
Rosarinho. FMNH 115080, 1, Rio Madeira, between Parana´
do Maraca´ and Parana´ Ipiranga, between Rosarinho and Vila
Urucurituba. FMNH 115081, 2, Rio Madeira, between Parana´
do Urucurituba and Rio Amazonas, between Vila Urucur-
ituba and Santa Maria. FMNH 115084, 1, Rio Amazonas,
between Rio Madeira and Parana´ do Serpa, between Santa
Antonia and Itacoatiara. FMNH 115086, 4, Rio Solimo˜es,
upstream of Rio Negro, upstream of Vila de Careiro. FMNH
115087, 16; FMNH 115088, 1, Rio Amazonas, downstream
of Rio Negro, downstream of Manaus. FMNH 115089, 88,
Rio Solimo˜es, upstream of Rio Purus, upstream of Anori.
FMNH 115090, 4; FMNH 115091, 8; FMNH 115092, 6;
FMNH 115106, 9, Rio Solimo˜es, downstream of Rio Purus.
FMNH 115093, 2; FMNH 115094, 21, Rio Amazonas,
upstream of Rio Madeira, upstream of Itacoatiara. FMNH
115095, 54, Rio Amazonas, upstream of tributary Rio
Madeira and Parana´ da Eva, upstream of Novo Oriente.
FMNH 115096, 11; FMNH 115097, 2, Rio Amazonas,
between Rio Negro and Rio Madeira, between Nova Oriente
and Itacoatiara. FMNH 115098, 1; FMNH 115099, 1; FMNH
115100, 1, Rio Madeira, between Parana´ do Canuma and Rio
Amazonas, between Nova Olinda do Norte and Vila
Urucarituba. FMNH 115101, 2, Rio Amazonas, between Rio
Madeira and Parana´ do Serpa, between Manaus and
Itacoatiara. FMNH 115102, 18, Rio Purus, between Lago do
Estopa and Rio Solimo˜es, between Surara and Beruri. FMNH
115103, 1, Rio Amazonas, between Rio Madeira and Parana´
do Serpa, between Santo Antoˆnio and Itacoatiara. FMNH
115104, 198, Rio Solimo˜es near Parana´ do Barrosa, between
Vila Iranduba and Vila Careiro. FMNH 115105, 1, Rio Purus,
Fig. 3. Holotype of Porotergus gimbeli, FMNH 54566, 200.0 mm, reproduced from Ellis (1913).
Fig. 4. Porotergus gimbeli from the Amazon River, near the city of Tefe´,
showing sexual dimorphism in cranial morphology. (A) MCP 37527
(sexually mature male, 202.0 mm). (B) MCP 37525 (sexually mature
female, 189.0 mm TL). Scale bar 510 mm.
de Santana and Crampton—Review of Porotergus 169

upstream of Rio Solimo˜es. FMNH 115107, 15; FMNH
115108, 9, Rio Solimo˜es, upstream of Rio Purus. FMNH
115109, 25, Rio Amazonas, upstream of Rio Purus. FMNH
115110, 15, Rio Amazonas, upstream of Rio Madeira. FMNH
115111, 34, Rio Amazonas, downstream of Rio Madeira,
upstream of Itacoatiara. INPA 11390, 93; INPA 11395, 41,
Rio Madeira, 10 km of Rio Amazonas. INPA 11416, 38, Rio
Amazonas, Parana´ do Tapai, near Rio Madeira. INPA 11487,
20, Rio Solimo˜es (near Ilha da Marchantaria), Iranduba.
INPA 11488, 9, Rio Solimo˜es (downstream of Rio Purus)
Beruri. INPA 11489, 1, Rio Purus near Rio Solimo˜es, Beruri.
INPA 11490, 12, Rio Solimo˜es, upstream of Rio Purus, Beruri.
INPA 11491, 1, Rio Solimo˜es, mouth of Lago Manacapuru,
Manacapuru. INPA 11492, 4, Rio Amazonas, Parana´do
Tapai, near Rio Madeira. INPA 11493, 17, Rio Amazonas,
Ilha do Careiro, Parana´ da Terra Nova, Careiro. INPA 11494,
1, Rio Solimo˜es near Rio Purus, Beruri. INPA 11495, 2, Rio
Amazonas downstream of Parana´ da Eva, Itacoatiara. INPA
11496, 1, Rio Solimo˜es downstream of Rio Coari, Coari.
INPA 13532, 1, Rio Solimo˜es, Ilha do Ic¸e´ , NW of Tefe´, Tefe´.
INPA 15800, 1; INPA 15804, 4, Rio Solimo˜es, Mamiraua´ lake
system, Parana´ Maina, Alvara˜es, 3u06.749S, 64u47.539W.
INPA 18189, 1, Rio Solimo˜es, south bank Ilha do Ic¸e´,
3u09.519S, 64u48.769W. MCP 37523, 2 (166–172), Rio
Solimo˜es, Mamiraua´ lake system, Parana´ Maina, Alvara˜es,
3u06.749S, 64u47.539W. MCP 37524, 3 (160–189), Rio Japura´-
Solimo˜es confluence, Praia Carborini, Alvara˜es, 3u09.749S,
64u47.069W. MCP 37525, 2 (175–189), Rio Japura´ near
mouth of Lago Mamiraua´, Alvara˜es, 3u07.749S, 64u46.439W.
MCP 37526, 1 (172), Mamiraua´ lake system, Parana´ Maiana,
Alvara˜es, 3u06.749S, 64u47.539W. MCP 37527, 4 (140–202),
Mamiraua´ lake system, Parana´ Maiana, Alvara˜es, 3u06.749S,
64u47.539W. MCP 37528, 1 (185), Rio Solimo˜es, near mouth
of Parana´ Coxiu Muni, Tefe´, 3u17.749S, 64u37.849W. MCP
37529, 2 (188–198), Rio Solimo˜es, Ilha do Prego, opposite
town of Alvara˜es, Alvara˜es, 03u12.639S, 64u47.389W. MCP
37530, 1 (197), Rio Japura´-Solimo˜es Confluence, Praia
Caborini, Alvara˜es, 3u09.149S, 64u47.069W. MCP 37531, 4
(155–195), Rio Solimo˜es, Ilha do Prego, opposite town of
Alvara˜es, 3u12.639S, 64u47.389W. USNM 373031, 86 (90–
205), Rio Japura´, 2.6 km below Serraria, 3u099130S,
64u469520W. USNM 373076, 95 (82–136), Rio Solimo˜es,
3u399310S, 61u289370W. USNM 373083, 27 (2 CS; 106–163),
Rio Amazonas, 26 km above Itacoatiara, 3u189460S,
58u359030W. USNM 373310, 11 (121–187), Rio Solimo˜es,
3u359430S, 61u079160W. USNM 375100, 1 (105), Rio Purus,
3u599270S, 61u299110W. USNM 375101, 1 (145), Rio Soli-
mo˜es, 3u359570S, 61u199480W. USNM 375107, 2 (112–132),
Rio Solimo˜es, near Rio Jutaı´, 3u369170S, 61u179000W. USNM
373099, 3 (150–189), Rio Solimo˜es, 25.9 km downstream of
Petrolina, 21.5 km upstream of Foz de Jutaı´2u439570S,
66u569130W. USNM 375103, 10 (88–145), Rio Madeira,
9 km upstream of Vila Urucarituba, 3u359260S, 58u589080W.
USNM 375109, 2 (125–143), Rio Jurua´ between Pauapixuna
and Tamanicoa, 2u469150S, 65u509100W. USNM 375099, 3
(122–145), Rio Solimo˜ es, upstream of Vila de Careiro,
3u149260S, 59u549330W. USNM 375102, 1 (134), Rio Soli-
mo˜es, 3u369410S, 61u009350W. USNM 375104, 6 (86–120),
Rio Madeira, 3 km downstream of Vila Urucarituba, 1 km
upstream of Itacoatiara, 3u329010S, 58u549170W. USNM
375105, 1 (116), Rio Madeira, 6 km downstream of Nova
Olinda do Norte, 43 km upstream of Vila Urucarituba,
3u499440S, 59u039320W. USNM 375106, 1 (153), Rio Soli-
mo˜es, 11 km above Siria, 24 km downstream of Petrolina,
2u459090S, 66u569230W. USNM 375108, 2 (120–132), Rio
Amazonas, upstream of Itacoatiara, 3u209200S, 31u029020W.
USNM 375110, 7 (117–135), Rio Purus, 2.1 km upstream of
Fazenda,5kmdownstreamofSa˜o Tome´, 3u459410S,
61u259570W. USNM 375111, 1 (139), Rio Solimo˜es,
26.5 km downstream of Alvara˜es, 53.7 km upstream of
Caiambe´, 3u189360S, 64u349540W. Para´: FMNH 54566 (ex
CM 3197), holotype (200), Amazon basin. FMNH 54567,
paratypes, 2 (166–240), no locality. FMNH 115076, 15;
FMNH 115077, 2, Rio Amazonas, between Furo de Urucur-
ic¸a´ia and Rio Xingu, between Almeirim and Gurupa´ . FMNH
115078, 1, Rio Amazonas, between Furo Macujubim and
Tambururi, between Antoˆnio Lemos and Vila Canaa˜. FMNH
115082, 14, Rio Trombetas, between Lago Iripixi and Lago
Cachoeiri, between Oriximina´ and Fazenda Paraı´so. FMNH
115083, 5, Rio Jari, between Monte Dourado and Paraguai.
FMNH 115085, 4, Rio Trombetas, between Rio Cumina´ and
Lago Axipica, between Bom Jesus and Santa Cecilia. FMNH
115112, 2, Rio Amazonas, between Rio Ituqui and Parana´de
Monte Alegre, between Santare´m and Monte Alegre. FMNH
115114, 3, Rio Amazonas, between Furo de Urucuric¸a´ia and
Parana´dos Arraiolos, between towns Almeirim and Gurupa´.
FMNH 115115, 1, Rio Jari, downstream of Monte Dourado.
FMNH 115116, 3; FMNH 115117, 1, Rio Amazonas, between
Rio Mojui and Furo do Tajapuru, between Gurupa´ and
Serraria. FMNH 115118, 6, Rio Amazonas, between Rio
Batata and Furo Tajapuruzinho, between Vila Canaa˜ and
Porto Sa˜o Jose´ . FMNH 115119, 3, Rio Amazonas, between
Rio Tauau and Estreito de Breves, upstream of Breves. FMNH
115120, 1, Rio Para´, between Rio Canaticu and Rio Boa
Vista, between Curralinho and Paqueta´. FMNH 115121, 6,
Rio Para´, between Rio Boa Vista and Rio Tocantins, between
Boa Vista and Abaetetuba. FMNH 115122, 1, Rio Amazonas,
between Rio Urucuric¸a´ ia and Xingu Arraiolos, between
towns Almeirim and Gurupa´ . FMNH 115125, 3, Rio
Amazonas, between Furo do Surubim-Ac¸u and Rio Tapajo´s,
between Cabec¸a da Onc¸a and Santare´m. INPA 4366, 9, Rio
Tocantins, Cameta´ market. INPA 11497, 30, Rio Amazonas,
downstream of mouth of Rio Tapajo´ s, Santare´m. USNM
372998, 33 (1 CS; 150–180); USNM 373007, 23 (117–174),
Rio Jari, downstream of Monte Dourado, 1u139560S,
52u059210W. USNM 373000, 1 (198), Rio Amazonas,
10.2 km upstream of Monte Alegre, 2u039480S, 53u579430W.
USNM 373306, 2 (179–190), Rio Amazonas, 43 km down-
stream of Gurupa´, 1u299330S, 52u129030W. USNM 373307, 1
(183), Rio Amazonas, 15 km upstream of Breves. USNM
373308, 2 (148–184), Rio Amazonas, 10.2 km upstream of
Monte Alegre, 2u059010S, 54u009050W. USNM 373309, 2
(165–176), Rio Amazonas, upstream of Rio Xingu, 41.5 km
upstream of Gurupa´, 1u269500S, 51u599020W. USNM 373084,
10 (110–210), Rio Amazonas, 17.8 km upstream of O
´bidos,
1u539230S, 55u569380W. USNM 373086, 20 (127–180), Rio
Amazonas, 7 km upstream of O
´bidos, 1u529560S,
55u349490W. USNM 373089, 5 (165–190), Rio Amazonas,
28 km upstream of Rio Juruti, 47.8 km upstream of O
´bidos,
2u019210S, 55u539420W. USNM 373110, 4 (140–195), Rio
Trombetas, 2.1 km upstream of Vila Aracua, 1u319000S,
56u079150W. USNM 373311, 2 (157–160), Rio Amazonas
47 km downstream of Almerim, 62.5 km upstream of
Gurupa´, 1u299230S, 52u119070W. USNM 373316, 1 (158),
Rio Amazonas, 18 km downstream of Porto de Moz,
1u369250S, 52u119460W. USNM 373861, 1 (174), Rio Amazo-
nas 10.2 km upstream of Monte Alegre, 2u059260S,
54u009080W. USNM 373862, 5 (156–173), Rio Amazonas
170 Copeia 2010, No. 1

between Almerim and Gurupa´, 1u289480S, 52u049150W.
USNM 374009, 8 (156–171), Rio Tocantins, 11 km down-
stream of Curucambaba, 24.8 km upstream of Maiuata,
2u029180S, 49u179330W. USNM 374010, 4 (168–171), Rio
Tocantins, 11 km downstream of Curucambaba, 2u029250S,
49u179300W. USNM 375097, 1 (153), Rio Amazonas, 90.2 km
downstream of Almerim, 21 km upstream of Gurupa´,
1u289210S, 51u489510W. USNM 375098, 1 (152), Rio Amazo-
nas, 15 km upstream of Breves, 1u359560S, 50u339190W. Peru:
CAS 31238, 1, Iquitos.
Diagnosis.—Porotergus gimbeli is diagnosed from all conge-
ners by the presence of a distinct swelling (an electrorecep-
tive structure) on the chin (versus absence), a pale straw
body pigmentation of preserved and live specimens (versus
light brown in P. duende, and dark brown in P. gymnotus), the
total anal-fin rays (171–198 versus 124–154), the prepec-
toral-fin distance (10.3–13.5%of LEA versus 14.1–18.0), the
presence of 6–8 small, conical teeth on the premaxilla in
adults (versus edentulous in P. duende, and two to three large
teeth in P. gymnotus), and the unossified second basibran-
chial (versus ossified in P. duende; condition unknown in P.
gymnotus). It is further diagnosed from P. duende by the
presence of two rows of conical teeth on the dentary (versus
one row). It is diagnosed from P. gymnotus by the head
length (10.0–13.0%of LEA versus 13.8–16.6), the distance
from the posterior naris to the snout (13.8–20.0%of HL
versus 23.6–31.7), the snout length (23.2–29.1%of HL
versus 31.5–36.3), and the tail depth (18.2–22.7%of CL
versus 6.8–12.9).
Description.—Head and body shape and pigmentation
illustrated in Figures 3 and 4. Morphometric data presented
in Table 1. Maximum examined body size 270 mm. Body
laterally compressed. Greatest body depth at abdominal
cavity, or slightly posterior to that area. Dorsal profile of
body nearly straight. Lateral line extending to base of caudal
fin, but absent on fin. Anterior-most perforated scale located
above pectoral-fin origin. Head laterally compressed, widest
at opercular region, deepest at nape. Dorsal profile of head
convex. Eye small, located laterally on head and completely
covered by thin membrane.
Upper jaw slightly longer than lower jaw. Mouth terminal.
Rictus located at vertical through anterior margin of eye.
Presence of distinct swelling (electroreceptive structure;
Albert, 2001) present on chin. Swelling on chin varies in
size, but present in all examined individuals. Anterior naris
located at end of small tube, and close to tip of snout.
Posterior naris ovoid, without tubular extension and closer to
eye than to tip of snout. Branchial opening located slightly
anterior to pectoral-fin origin. Branchial membranes joined
at isthmus. Anus and urogenital papilla adjacent, located
ventral to head, with position located approximately at
vertical through eye or, along vertical two orbital diameters
posterior to eye. Premaxilla of moderate size, with 6–8 small,
conical teeth. Dentary with two tooth rows, with 16 conical
functional plus three replacement teeth. First basibranchial
ossified. Posterior basibranchials cartilaginous.
Pectoral fin broad and distally pointed, with 14–17 [15] (n
538) rays. Anal-fin origin located anterior to vertical
through posterior margin of opercle. Total anal-fin rays
171–198 [175] (n521). Scales absent along entire middorsal
region of body. Scales above lateral line to middorsal line 5–
6 [6] (n537). Dorsal mid-sagittal electroreceptive filament
inserted into narrow mid-dorsal groove. Origin of filament
located at 50%of TL. Filament extending posteriorly 2–3
scales beyond vertical through rear of base of anal fin. Tail
compressed and short, ending in small, lanceolate caudal
fin. Caudal-fin rays 14–17 [14] (n510). Caudal fin
frequently missing or partially regenerated. Precaudal
vertebrae 15 (13 anterior, 2 transitional, n510).
Secondary sexual dimorphism.—Sexually mature males exhib-
it slightly more elongate snouts than do females (Fig. 4).
Coloration in life.—Uniformly pale with pinkish hue caused
by capillaries under skin, especially over anal-fin pterygio-
phores. Very sparse scattering of light brown chromato-
phores on dorsal surfaces of head and body. Dorsal surface
brown with tuberous electroreceptors visible as white dots.
Operculum pink due to underlying gills. Eye dark, covered
with translucent membrane. Pectoral, anal, and caudal fins
with hyaline membranes. Specimens of P. gimbeli show
similar pigmentation patterns in both white- and blackwater
systems.
Coloration in alcohol.—Head and body uniformly pale straw
to tan, darker dorsally with brown middorsal region.
Electric organ discharges.—Crampton and Albert (2006)
report P. gimbeli to generate a wave-type EOD with a
fundamental frequency of 1156–1377 Hz (mean 1264, SD
71.2, n520), and illustrate the EOD and PSD plot from a
single immature specimen (INPA 15800, 146 mm). The EOD
waveform contains two phases of alternating polarity,
corresponding to a type-C category of apteronotid EOD
(sensu Crampton and Albert, 2006). Sexual differences in
EOD waveform and EOD discharge rate were not observed
(males: 1167–1316 Hz, mean 1246.3, SD 65.1, n54;
females: 1230–1377, mean 1299.8, SD 49.7, n510;
immature: 1156–1375, mean 1.220, SD 72.6, n58). Among
all recorded specimens (immature and mature) we noted
subtle variation in EOD waveform, but all corresponded to a
type-C discharge. The peak power frequency corresponds
invariably to the fundamental frequency (n520). No
spontaneous amplitude modulations (chirps) or other EOD
modulations were observed.
Ecology.—In the Tefe´ region, Porotergus gimbeli is known
from the main channels of sediment-rich whitewaters (e.g.,
Rio Solimo˜es) and low-conductivity, sediment-poor black-
waters (e.g., Rio Tefe´). Porotergus gimbeli was commonly
encountered in the main channel of the Rio Solimo˜ es,
including in trawl net samples at depths of 5–15 m, and from
seine nets operated on beaches (especially at night). Only a
few specimens were captured in the Rio Tefe´, all from trawl net
samples at depths of 5–14 m. The chemistry of the Rio Tefe´
differs from that of the Rio Solimo˜es (see P. duende Ecology
section) in its lower conductivity (6–30 m
Sc21
) and low pH (5.0–
6.7). Suspended sediment loads are generally low in the Rio
Tefe´, except at the lowest water levels. As in the Rio Solimo˜es,
dissolved oxygen levels are perpetually relatively high (3.5–
6.0 mg/l). Breeding of P. gimbeli in the Tefe´regionoccurs
during the rising water period, and adults probably spawn in
floating meadows along the edge of parana´ channels (side
branches of whitewater rivers running through adjacent
va´rzea floodplains). Some post-larval specimens tentatively
identified as P. gimbeli were found in floating meadows along
de Santana and Crampton—Review of Porotergus 171

whitewater channels/parana´s of the Rio Solimo˜es, but not in
floating vegetation along the Rio Tefe´.
Stomach content analyses indicate that Porotergus gimbeli
feeds on small, autochthonous, benthic insect larvae
including micro-caddis fly larvae (Trichoptera: Hydroptili-
dae), dipteran larvae (mostly Ceratopogonidae and Chir-
onomidae), beetle larvae (Coleoptera), and Ephemeroptera.
Small crustaceans (conchostracans and ostracods) were
found in some stomachs.
Distribution.—Porotergus gimbeli is known from the Amazon
River basin in Brazil and Peru (Fig. 5). Although Ellis (in
Eigenmann, 1912, 1913) cited the occurrence of an
uncatalogued co-type of P. gimbeli from Guyana at Ubabu
Creek, we were unable to find any type or non-type
specimens from that region.
Remarks.—Some museum lots of P. gimbeli demonstrated
differences in the size of the chin swelling (e.g., USNM
373099). Variation in the size of chin swelling did not
appear to be correlated with external morphology, meristic
characters, size, sex, or geographical distribution. None of
these unusual specimens exhibited other diagnostic mor-
phometric or meristic differences, but the possibility of
additional cryptic species deserves future attention.
Porotergus gymnotus Ellis, 1912
Figures 6, 7; Table 1
Porotergus gymnotus.—Ellis in Eigenmann, 1912:441 [type
locality: Amatuk, Guyana].–Ellis, 1913:153, pl. 23, fig. 4
[Guyana; first illustration].–Henn, 1928:71 [in listing of
type species].–Mago-Leccia, 1994:32, 148, fig. 42 [range
reported as Amazon and Guianas; illustration—specimen
faded, not exhibiting typical dark pigmentation].–Albert
and Campos-da-Paz, 1998:433 [in listing of members of
genus].–Albert, 2001:78, 91 [in listing of members of
genus; range reported as Amazon and Guianas].–Albert,
2003:500 [Brazil, French Guiana, and Guyana].
Material examined.—Guyana. Amatuk: BMNH 1911.10.
31.543, paratype, 1 (77). CAS 62305 (ex IU 12636), paratype,
1 (85), Essequibo River, Potaro River. CAS 31237, 2 (87–102),
Essequibo River, Warraputa Cataract. CAS 72234, 2 (97–
113), Essequibo River, Potaro River. FMNH 53575 (ex CM
1759), holotype (65.2), Essequibo River, Warraputa Cataract.
FMNH 53291, paratype, 1 (57.8), Essequibo River, Kona-
waruk River (as presented by Ellis, 1912:441).
Diagnosis.—Porotergus gymnotus is diagnosed from all conge-
ners by the presence of a dark brown body pigmentation
(versus light brown in P. duende, and pale straw in P. gimbeli)
and the two large conical teeth on the premaxilla (versus
edentulous in P. duende, and six to eight small teeth in P.
gimbeli). It is further diagnosed from P. duende by the
distance from the posterior naris to the eye (8.2–11.9%of HL
versus 1.7–3.8), the mouth length (28.1–38.7%of HL versus
12.4–27.4), the pectoral-fin length (60.4–70.7%of HL versus
72.7–89.0), and the dentary with two rows of conical teeth
(versus one row). It is diagnosed from P. gimbeli by the
absence of a distinct swelling on the chin (versus presence of
that structure), the total anal-fin rays (129–147 versus 171–
198), the head length (13.8–16.6%of LEA versus 10.0–13.0),
the snout length (31.5–36.3%of HL versus 23.2–29.1), the
distance from the posterior naris to the snout (23.6–31.7%
of HL versus 13.8–20.0), the prepectoral-fin distance (16.8–
18.0%of LEA versus 10.3–13.5), and the tail depth (6.8–
12.9%of CL versus 18.2–22.7).
Description.—Head and body shape and pigmentation
illustrated in Figures 6 and 7. Maximum examined body
size 113 mm. Morphometric data presented in Table 1. Body
laterally compressed. Greatest body depth at abdominal
cavity or slightly posterior of that area. Dorsal profile of
body nearly straight. Lateral line extending to base of caudal
fin, but absent on fin. Anterior-most perforated scale located
above pectoral-fin origin. Head laterally compressed, widest
at opercular region, deepest at nape. Dorsal profile of head
convex. Eye small, located laterally on head and completely
covered by thin membrane.
Upper and lower jaws equal. Mouth terminal. Rictus
located at vertical through anterior margin of eye. Anterior
naris located at end of small tube and close to tip of snout.
Posterior naris ellipsoid, without tubular extension and
closer to eye than to tip of snout. Branchial opening located
slightly anterior to pectoral-fin origin. Branchial membranes
joined at isthmus. Anus and urogenital papilla adjacent,
located ventral to head, with position located approximately
at vertical along vertical two orbital diameters posterior to
eye, but without noticeable forward displacement ontoge-
netically. Premaxilla of moderate size, with two large conical
teeth. Dentary with two tooth rows, with ten conical teeth
in total.
Pectoral fin broad and distally pointed, with 13–14 [14] (n
56) rays. Anal-fin origin located anterior to vertical through
posterior margin of opercle. Total anal-fin rays 129–147
[129] (n55). Scales absent along entire middorsal region of
body. Scales above lateral line to middorsal line 4–5 [5] (n5
6). Dorsal mid-sagittal electroreceptive filament inserted
into narrow mid-dorsal groove. Origin of filament located at
50%of TL. Filament extending 2–4 scales posterior of
vertical through rear of base of anal fin. Tail compressed
and short ending in small, lanceolate caudal fin. Caudal-fin
rays 12–19 [19] (n57). Precaudal vertebrae 15–16 (13
anterior, 2–3 transitional, n53).
Coloration in alcohol.—Head and body coloration uniformly
dark brown, specimens that have been preserved for long
periods of time more faded. Pectoral- and anal-fin mem-
branes hyaline. Caudal fin brown.
Fig. 5. Geographic distribution of Porotergus gimbeli (squares; precise
type locality unknown, but possibly near the city of Bele´ m do Para´ [1]),
and Porotergus gymnotus (dots; 2 5type locality at Essequibo River).
Some symbols represent more than one lot or locality.
172 Copeia 2010, No. 1

Secondary sexual dimorphism.—No sexual dimorphism of the
cranial or post-cranial morphology or of the pigmentation
was observed in sexually mature specimens.
Distribution.—Porotergus gymnotus is only known from the
Essequibo drainage in Guyana (Fig. 5).
Remarks.—Although P. gymnotus is restricted to Guyana, we
noted that museum specimens of more than one small
species of apteronotid collected from the Amazon basin are
often incorrectly labeled P. gymnotus. A minority of the
incorrectly labeled specimens proved to be P. duende (these
are listed above). The majority, however, belong to two or
more undescribed species of the genus Compsaraia (see list of
material examined).
Material identified by Planquette et al. (1996:figure on
p. 409) as P. gymnotus, and listed as occurring in the Maroni
and Mana basins in French Guiana appears not to be P.
gymnotus, but instead an undescribed species of apteronotid
(although specimens were unavailable for examination).
DISCUSSION
It is common to find museum specimens labeled as
Porotergus that are rather in fact Compsaraia. The genus
Compsaraia consists of C. compsus,C. samueli, and a number
of additional undescribed species. In addition to the
diagnostic characters used to recognize members of Por-
otergini, which are absent in Compsaraia, herein we
emphasize the differences between species of Compsaraia
(non-Porotergini) and Porotergus (Porotergini) to eliminate
future taxonomic confusion, and also highlight differences
between Porotergus and other apteronotid genera within the
tribe Porotergini. The following characters unambiguously
distinguish species of Porotergus from Compsaraia:the
absence of a pale stripe of low melanophore density forming
a narrow band passing anterior to the eyes and lateral to the
nares, and the poorly ossified infraorbital series.
Species of Porotergus can be distinguished from Sternarch-
ogiton by the presence of a maxilla without an anterior shelf
(versus a sharp angle along the ventral margin of the
descending blade of the maxilla positioned about two-thirds
of the distance to its tip). In contrast to Adontosternarchus,
scales are absent on the middorsal region of all species of
Porotergus and Sternarchogiton. Moreover, Porotergus can be
distinguished from Adontosternarchus by the presence of
teeth on the dentary in adults (versus absence of teeth on
the dentary). Notwithstanding the efforts in recent years to
resolve the taxonomy within the Porotergini (Mago-Leccia
et al., 1985; de Santana and Crampton, 2007), it is obvious
Fig. 6. Holotype of Porotergus gymnotus, FMNH 53575, 65.2 mm, reproduced from Ellis (1913). Note that Ellis registered a total length of 70.0 mm.
Fig. 7. Paratype of Porotergus gymnotus, CAS 62305 (85.0 mm), from Amatuk, Guyana. Scale bar 510 mm.
de Santana and Crampton—Review of Porotergus 173

that a more encompassing study, involving a phylogenetic
analysis, is necessary to address limits of the genera
Adontosternarchus,Porotergus, and Sternarchogiton.
KEY TO THE SPECIES OF POROTERGUS
1a. Chin with prominent swelling, Fig. 4; prepectoral-
fin distance 10.3–13.5%of LEA; 171–198 anal-fin
rays
___________________________________________________________
Porotergus gimbeli
(Amazon basin, Brazil and Peru)
1b. Chin lacking prominent swelling; prepectoral-fin
distance 14.1–18.0%of LEA; 124–154 anal-fin rays
________________________________________________________________________________________________________
2
2a. Teeth absent on premaxilla; distance from posteri-
or naris to eye 1.7–3.8%of HL; mouth length 12.4–
27.4%of HL
_______________
Porotergus duende, new species
(Western Amazon basin, Brazil and Peru)
2b. Two large teeth present on premaxilla; distance
from posterior naris to eye 8.2–11.9%of HL; mouth
length 28.1–38.7%of HL
__________
Porotergus gymnotus
(Essequibo River drainage, Guyana)
MATERIAL EXAMINED
Alcohol preserved material.—Apteronotus sp.: Guyana. Ama-
tuk: INHS 49455, 1 (127), Potaro River, Essequibo River,
beach on north bank, downstream of Tumatumari Cataract,
5u21.489N, 59u00.049W.
Compsaraia sp.: Brazil. Amazonas: MCP 24163, 1 (88.5),
Rio Negro, 18. 5 mi upstream of Manaus, 3u49520S,
60u109590W. USNM 375157, 7 (120–140), Rio Amazonas
62.5 km upstream of Gurupa´, 1u299230S, 52u119070W. USNM
375158, 3 (90–129), Rio Solimo˜es upstream of Careiro,
3u149260S, 59u549330W. USNM 375159, 4 (73–108), Rio
Purus. USNM 375160, 9 (80–148), Rio Madeira, 3u359540S,
58u589080W. USNM 375161, 1 (85), Rio Amazonas upstream
of Itacoatiara, 3u199500S, 58u359410S. USNM 375162, 7 (107–
142), Rio Negro 9 mi upstream of Manaus 3u039030S,
60u139160W. USNM 375163, 8 (88–115), Rio Madeira 9 km
upstream of Vila Urucatiruba, 3u359260S, 58u589080W. USNM
375164, 7 (60–141), Rio Madeira 4.5 km upstream of Vila
Urucatiruba, 3u349440S, 58u579020W. USNM 375165, 21 (77–
127), Rio Madeira 1 km upstream of Itacoatiara, 3u329010S,
58u549170W. USNM 375166, 1 (116), Rio Trombetas, 2.1 km
upstream of Aracua. USNM 375167, 6, Rio Negro 0.25 km
upstream of Paricatuba, 3u039200S, 60u149000W. USNM
375168, 10 (113–153), Rio Negro 7 mi downstream of Santa
Maria, 3u019590S, 60u239060W. USNM 375169, 10 (91–109),
Rio Solimo˜es, 3u399260S, 61u289320W. USNM 375170, 3 (89–
119), Rio Solimo˜es, 3u359430S, 61u079160W. USNM 375171, 1
(98), Rio Madeira downstream of Nova Olinda, 3u379360S,
59u019110W. USNM 375172, 2 (106–116), Rio Amazonas
upstream of Itacoatiara, 3u209200S, 31u029020W. USNM
375173, 8 (120–155), Rio Negro, 18.5 km upstream of
Manaus, 3u059280S, 60u119050W. USNM 375174, 1 (102),
Rio Amazonas 33.5 km downstream of Manaus, 3u029500S,
59u459580W. USNM 375175, 8 (82–132), Rio Amazonas,
4.4 km downstream of Novo Oriente. Venezuela: Bolivar:
ANSP 162708, 4 (54–97), confluence of Rı´o Orinoco and Rio
Caura, 7u389360N, 64u500W. MBUCV 15275, 1 (52), same
locality of ANSP 162708.
Cleared and stained material.—Adontosternarchus devenanzii:
MBUCV 12779, 1. Adontosternarchus sachsi: FMNH 100742,
1. Apteronotus albifrons: MCZ 52011, 1; MCZ 52013, 1.
Apteronotus apurensis: USNM 228869, 1. Apteronotus rostratus:
MBUCV 10926, 2. Magosternarchus duccis: USNM 373268, 1.
Megadontogathus kaitukaensis: INPA 3936, 1. Orthosternarchus
tamandua: USNM 373072, 2; USNM 373017, 1. Sternarchella
orthos: FMNH 100746, 1. Sternarchogiton labiatus:MCP
37545, 1. Sternarchorhamphus muelleri: USNM 228807, 6.
Sternarchorhynchus caboclo: INPA 10594, 2. Sternarcho-
rhynchus curumim: INPA 25256, 1.
ACKNOWLEDGMENTS
J. Alves-Gomes, D. Catania, F. Lima, J. Lima Figueiredo, J.
Lundberg, L. Page, L. Rapp Py-Daniel, M. Retzer, R. Robins,
M. Rogers, M. Sabaj, R. Vari, P. Willink, and R. Winterbot-
tom provided access to specimens. We acknowledge the
Calhamazon Project (National Science Foundation DEB
9300151), J. Lundberg, PI, for making available a substantial
portion of the specimens examined here. The authors are
grateful to M. Hoang for the photograph of P. gymnotus. CDS
is indebted to the Instituto Nacional de Pesquisas da
Amazoˆnia, a Smithsonian Predoctoral Fellowship in the
Division of Fishes, National Museum of Natural History, and
a Postdoctoral fellowship from the University of Central
Florida. WGRC was funded by the Conselho Nacional de
Pesquisas e Desenvolvimento Tecnolo´ gico (CNPq) (grants
38062/96-2 and 381597/97–0 plus extensions) and National
Science Foundation (grants DEB-0614334 and DEB-
0102593). Collecting was authorized by Instituto Mamiraua´
and IBAMA permit 0492/99-12 (and extensions) to WGRC.
Animal care protocols follow CNPq guidelines. This paper
benefited from comments by R. P. Vari and S. H. Weitzman.
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