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Petrocephalus leo, a new species of African electric fish (Osteoglossomorpha: Mormyridae) from the Oubangui River basin (Congo basin)

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A new species of the African weakly electric fish genus Petrocephalus (Osteoglossomorpha: Mormyridae: Petrocephalinae) is described from the Oubangui (Ubangi) River basin, the principal right-bank tributary of the Congo River. Petrocephalus leo sp. nov. is one of the most distinctive species of Petrocephalus as it combines (among other characteristics) the absence of electroreceptive rosettes on the head with a unique melanin pattern. Only four other species of Petrocephalus lack all electroreceptive rosettes: Petrocephalus microphthalmus, Petrocephalus haullevillii, Petrocephalus schoutedeni, and Petrocephalus zakoni. Petrocephalus leo sp. nov. can be distinguished from these four species in having a distinctive black mark at the base of the pectoral fins (versus absent in P. microphthalmus, P. haullevillii and P. schoutedeni) and no subdorsal black mark (versus present in P. zakoni). A phylogenetic analysis using mitochondrial cytochrome b gene sequences shows haplotypes of P. leo sp. nov. are distinct, but are unexpectedly nested within P. zakoni haplotypes, making this latter species paraphyletic. To investigate this conflict between morphology and mitochondrial cytochrome b, a nuclear marker, the first intron of the gene coding for the S7 ribosomal protein, was sequenced. The presence of four diagnostic indels between P. zakoni and P. leo sp. nov. sequences supports the reciprocal monophyly of these two species. This is the first reported case of conflict between morphology and mitochondrial phylogeny within the genus Petrocephalus. Finally, three species of Petrocephalus are reported for the first time from the Oubangui region bringing the total of Petrocephalus species in this region to 12.
Schematic drawing of Petrocephalus leo sp. nov., holotype, 76.1 mm standard length. Drawn by Yi-Hsuan Lin. Absence of the three typical Petrocephalus electroreceptive rosettes on the head distinguish P. leo sp. nov. from most of its congeners. Only four other species of Petrocephalus lack all three electoreceptive rosettes: Petrocephalus microphthalmus, Petrocephalus haullevillii, Petrocephalus schoutedeni Poll 1954, and Petrocephalus zakoni. Petrocephalus leo sp. nov. can be easily distinguished from these species (and all other species of Petrocephalus) by its unique pattern of melanin markings: a distinct black spot at the origin of the pectoral fins but no subdorsal pigmentation mark. Petrocephalus microphthalmus, P. haullevillii, and P. schoutedeni lack a black mark at the origin of the pectoral fins and P. zakoni possesses a distinct subdorsal pigmentation mark below the anterior base of the dorsal fin which often extends onto the first dorsal rays and makes contact over the dorsum with the contralateral mark (Figure 2; Lavoué et al. 2010). Petrocephalus leo sp. nov. can be further distinguished from Petrocephalus zakoni by its slender body (SL/H= 2.9-3.4, mean= 3.2; holotype=3.3 versus 2.5-2.7 [mean = 2.6] in P. zakoni); its relatively shorter dorsal fin (SL/DFL= 4.4-5.0, mean= 4.6; holotype=4.6 versus 4.0-4.3 [mean = 4.1] in P. zakoni) and its smaller eye (HL/ED= 3.7-4.4, mean= 4.0; holotype=3.7 versus 3.1-3.3 [mean = 3.2] in P. zakoni). Petrocephalus leo sp. nov. can be further distinguished from P. microphthalmus, P. haullevillii, and P. schoutedeni, by a higher dorsal-fin ray count (range= 21-24, mean and holotype = 22 versus <20 in P. microphthalmus, P. haullevillii, and P. schoutedeni). Live coloration (Figure 2). Body background brown/copper with metallic reflection on flanks, darker dorsally with belly whitish/silver with many dense melanophores visible. Caudal peduncle darker and lower margin of dorsal and anal fins blackish. A distinct black mark at base of the pectoral fins and a crescent-shaped mark at base of the caudal fin extending onto upper and lower lobes of caudal fin. All fins mostly whitish-brownish and translucent, anterior of dorsal fin darker. Eye black. Distribution (Figure 1). Petrocephalus leo sp. nov. is only known from two adjacent localities along the course of the Kotto River (Oubangui River basin). Electric organ discharge. Unknown. Electrocyte anatomy not studied; all Petrocephalus species examined have electric organ of type "NPp" (Lavoué et al. 2008). Etymology. This species is named after my son Léo (Latin name leo).
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Accepted by R. Mayden: 5 Apr. 2016; published: 9 Jun. 2016
ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN
1175-5334
(online edition)
Copyright © 2016 Magnolia Press
Zootaxa 4121 (3): 319
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Article
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http://doi.org/10.11646/zootaxa.4121.3.6
http://zoobank.org/urn:lsid:zoobank.org:pub:9A1F1AD6-7BFF-4229-A1D7-2ECD9600802E
Petrocephalus leo, a new species of African electric fish (Osteoglossomorpha:
Mormyridae) from the Oubangui River basin (Congo basin)
SÉBASTIEN LAVOUÉ
1
Institute of Oceanography, National Taiwan University, Roosevelt Road, Taipei 10617, Taiwan. E-mail: microceb@hotmail.com
1
http://zoobank.org/6DC89A1D-15B4-481F-9369-525CF0162FEB
Abstract
A new species of the African weakly electric fish genus Petrocephalus (Osteoglossomorpha: Mormyridae: Petrocephali-
nae) is described from the Oubangui (Ubangi) River basin, the principal right-bank tributary of the Congo River. Petro-
cephalus leo sp. nov. is one of the most distinctive species of Petrocephalus as it combines (among other characteristics)
the absence of electroreceptive rosettes on the head with a unique melanin pattern. Only four other species of Petroceph-
alus lack all electroreceptive rosettes: Petrocephalus microphthalmus, Petrocephalus haullevillii, Petrocephalus schout-
edeni, and Petrocephalus zakoni. Petrocephalus leo sp. nov. can be distinguished from these four species in having a
distinctive black mark at the base of the pectoral fins (versus absent in P. microphthalmus, P. haullevillii and P. schoutede-
ni) and no subdorsal black mark (versus present in P. zakoni). A phylogenetic analysis using mitochondrial cytochrome b
gene sequences shows haplotypes of P. l eo sp. nov. are distinct, but are unexpectedly nested within P. zakoni haplotypes,
making this latter species paraphyletic. To investigate this conflict between morphology and mitochondrial cytochrome b,
a nuclear marker, the first intron of the gene coding for the S7 ribosomal protein, was sequenced. The presence of four
diagnostic indels between P. zakoni and P. le o sp. nov. sequences supports the reciprocal monophyly of these two species.
This is the first reported case of conflict between morphology and mitochondrial phylogeny within the genus Petroceph-
alus. Finally, three species of Petrocephalus are reported for the first time from the Oubangui region bringing the total of
Petrocephalus species in this region to 12.
Key words: fish, Petrocephalinae, Africa, morphology, molecular phylogeny, cytochrome b, nuclear S7 intron
Résumé
Une nouvelle espèce de poissons électriques africains du genre Petrocephalus (Osteoglossomorpha: Mormyridae: Petro-
cephalinae) est décrite du bassin du fleuve Oubangui, le principal affluent droit du fleuve Congo. Petrocephalus leo sp.
nov. est l’une des espèces de Petrocephalus les plus distinctives en raison de l’absence de rosette électroréceptive sur la
tête et d’un patron de coloration unique. Seules quatre autres espèces de Petrocephalus n’ont aucune rosette
électroréceptive : Petrocephalus microphthalmus, Petrocephalus haullevillii, Petrocephalus schoutedeni et Petrocephalus
zakoni. Petrocephalus leo sp. nov. peut-être distinguée de ces espèces par la présence d’une tache noire à la base de la
nageoire pectorale (versus absente chez P. microphthalmus, P. haullevillii et P. schoutedeni) conjuguée à l’absence de
tache sous-dorsale (versus présente chez P. zakoni). Une analyse comparative fondée sur le gène du cytochrome b montre
que les deux haplotypes séquencés de P. le o sp. nov. sont distincts mais ils sont insérés au sein de P. z ak o n i rendant cette
dernière espèce paraphylétique. Pour tenter de résoudre le conflit entre la morphologie et le gène du cytochrome b, le pre-
mier intron du gène nucléaire codant la protéine ribosomale S7 est déterminé. La présence de quatre insertions/délétions
diagnostiques entre P. zakoni et P. l e o sp. nov. soutient la monophylie réciproque de chacune de ces deux espèces. C’est
le premier cas de conflit entre données morphologiques et mitochondriales dans le genre Petrocephalus. Finalement, trois
espèces de Petrocephalus sont pour la première fois mentionnées de la région de l'Oubangui portant le total d'espèces de
Petrocephalus dans cette région à
12.
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Introduction
Petrocephalus Marcusen 1854 is the most speciose genus of the African weakly electric fish family Mormyridae
(Teleostei: Osteoglossomorpha). It currently includes 45 valid species (46 with the new species described herein)
(Sullivan & Lavoué 2016). About one-third of the species of Petrocephalus were described during the last decade,
making use of diverse morphological, electrophysiological and genomic characters (Kramer et al. 2012; Lavoué
2011;2012; Lavoué et al. 2004; Lavoué et al. 2010; Lavoué & Sullivan 2014).
The subfamily Petrocephalinae comprises only one genus, Petrocephalus, and it is the sister group of the more
speciose subfamily Mormyrinae that includes 20 genera and more than 180 species (Sullivan et al. 2000; 2016;
Taverne 1972). Several morphological characters readily distinguish Petrocephalus and the mormyrin genera, such
as the presence of two closely apposed nostrils (versus non closely apposed in mormyrins) and the absence of the
basisphenoid bone (versus presence in mormyrins; Taverne 1972). Fossil-calibrated, Bayesian Relaxed Clock
phylogenetic analysis suggests the Petrocephalus lineage originated at approximately the Cretaceous-Paleogene
transition (Lavoué et al. 2012) and its extant representatives are broadly distributed in freshwater habitats across
tropical and subtropical Africa where they are often locally abundant (Lavoué et al. 2010; Paugy et al. 2008).
Despite its ancient origin and present-day abundance, there is no fossil record of Petrocephalus.
The Oubangui (Ubangi) River is the principal right-bank tributary of the Congo River, the largest freshwater
basin in Africa, covering roughly four millions km
2
in the center of the continent (Figure 1). The Oubangui River
drainage basin itself covers about 770,000km
2
. The Oubangui River originates at the confluence of the Uele (Uélé)
and Mbomou Rivers and discharges into the Congo River downstream of the city of Mbandaka in D.R. Congo. Its
basin is divided into two ecoregions (Thieme et al. 2005): the Uele Ecoregion (#74) corresponds to the Uele River
basin while the larger Sudanic Congo-Oubangui Ecoregion (#30) comprises the central and lower parts of the
Oubangui River basin along with a stretch of the Congo River. In the absence of apparent physical barriers (like
falls or rapids) isolating the Sudanic Congo-Oubangui region to downstream regions of the Congo basin, such as
the Cuvette Centrale (#18), Pool Malebo (#24) and Sangha (#27), the fauna of these regions are likely rather
homogeneous and the difference in species composition may only be related to differences in the prevailing
hydrological or climatic conditions.
Published records of Petrocephalus from the Oubangui River basin are few. Whereas 14 valid species are
recognized from the central basin of the Congo River (Lavoué et al. 2010; Lavoué & Sullivan 2014), only eight
species are reported from the whole Oubangui River basin. Boulenger (1902) reported Petrocephalus simus
Sauvage 1879 from Banzyville (today Mobayi-Mbongo in D.R. Congo). The Museum National d’Histoire
Naturelle (Paris) housed several specimens of Petrocephalus from this region collected by Alfred Baudon in the
1910s and identified by Pellegrin (1920) as Petrocephalus grandoculis Boulenger 1920, Petrocephalus sauvagii
Boulenger 1887 and Petrocephalus haullevillii Boulenger 1912. Almost fifty years later, Jean-Pierre Gosse (Gosse
1968) added Petrocephalus balayi Sauvage 1883, Petrocephalus christyi Boulenger 1920, and Petrocephalus
microphthalmus Pellegrin 1908. The presence of P. simus in the Congo basin still needs to be confirmed: so far, all
specimens previously identified as P. simus from the Congo basin have been found to belong to other species when
reexamined (Lavoué 2012; Lavoué et al. 2010; unpublished observations). Taverne (1972) added one species of
Petrocephalus to the Oubangui basin, when he reallocated Marcusenius hutereaui Boulenger 1913, described from
Dungu on the Uele River, to the genus Petrocephalus. With the exception of Petrocephalus hutereaui, only known
from its type locality, and P. simus, a likely endemic of the Lower Guinea ichthyofaunal province, the other six
species are also known from the Sangha River basin and the Cuvette Centrale of the Congo River basin.
Based on the examination of a fish collection made in 2006 by John P. Friel, Roger Bills and Duncan Reid
from several localities of the central part of the Oubangui River basin, I herein describe a new species of
Petrocephalus and report the occurrence of three species new to this region.
Material and methods
Specimen sampling. Petrocephalus specimens examined in this study come from the central Oubangui River
basin in Central African Republic: two localities on the Oubangui River at Bangui, two localities on the Kotto
River and two localities on the Ouaka River, both right-bank tributaries of the Oubangui (Figure 1). John P. Friel,
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Roger Bills and Duncan Reid collected all specimens, now housed at the Cornell University Museum of
Vertebrates. Comparative material including type specimens from all valid species from the Lower Guinea and the
Congo provinces is listed in Lavoué et al. (2004; 2010), Lavoué (2012) and Lavoué & Sullivan (2014). The nearly
complete sequence of the cytochrome b gene (the first nine bases are missing at the 5’ end) was determined for two
specimens of the new species and three additional specimens of Petrocephalus zakoni Lavoet al. 2010 (two
from the Oubangui basin and one from the Kisangani region, central Congo basin). In addition, the first intron of
the nuclear gene coding for the S7 ribosomal protein was determined for two specimens of the new species and
four specimens of P. z a k o n i (two from the Odzala-Kokua National Park, R. Congo, one from the Oubangui basin,
C.A.R., and one from the Kisangani region, central Congo basin, D.R. Congo).
FIGURE 1. Map of the hydrographic system of the central part of the Oubangui River basin showing the Petrocephalus
localities surveyed (top-left inset showing the location of the Congo basin in Africa). Filled black and open stars indicate the
type locality and the second locality on the Kotto River, respectively, of Petrocephalus leo sp. nov.
Morphology. The sex of each preserved specimen was determined by examining the body profile along the
base of the anal fin (Pezzanite & Moller 1998) and classified as "sexually mature males" when the base is strongly
indented or "sex undetermined" when the base is nearly straight.
Methods for making counts and measurements and abbreviations and definitions for each of these counts and
measurements follow those given by Boden et al. (1997) and Lavoué et al. (2004). The specimens were examined
for the presence of the three clusters of Knollenorgan-type electroreceptors on the head of Petrocephalus (Harder
1968; 2000). The Augenrosettes are above the anterior half of the left and right eyes, the Nackenrosettes are
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dorsally situated on each side of the nape, slightly anterior to the opercular openings and the Kehlrosettes are
situated in front of and below the insertion of the pectoral fins (Lavoué et al. 2010).
DNA sequencing and comparative methods. DNA was extracted from 90% ethanol-preserved fin clips or
dorsal muscle samples. PCR amplification and sequencing of the cytochrome b gene and the first intron of the
nuclear gene coding for the S7 ribosomal protein were as described by Sullivan et al. (2000) and Lavoué et al.
(2003), respectively. The cytochrome b gene was amplified using the following Petrocephalus-specific primers:
L14740_pet (5'-CCG TTG TAT TCA ACT ACA GAA-3'); and H15913_pet (5'-TCG ATC TCC GGA TTA CAA
GAC CG-3'). I amplified the complete (about 500 bp) first intron of the nuclear gene coding for the S7 ribosomal
protein using the two following primers, described by Chow & Hazama (1998): S7RPEX1F (5'-TGG CCT CTT
CCT TGG CCG TC-3') and S7RPEX2R (5'-AAC TCG TCT GGC TTT TCG CC-3'). PCR products were purified,
then sequenced by Sanger technology using the same primers. Accession numbers KF181723 to KF181726 in
Genbank database correspond to sequences generated in this study.
The new cytochrome b sequences were added to the dataset published in Lavoué & Sullivan (2014). The
alignment does not require any indels and the final alignment comprises 1140 nucleotidic positions. Considering all
positions and types of substitution equally, the maximum likelihood phylogenetic tree was calculated under the
general time reversible model of nucleotide substitution with rate heterogeneity following a discrete gamma
distribution (GTR+Г), using the software RAxML (Stamatakis 2006) and its graphical interface raxmlGUI
(Silvestro & Michalak 2012). As the new species and P. z a k o n i were found to be closely related in this
phylogenetic tree (not shown), their cytochrome b sequences were extracted and compared to search for discrete
nucleotide differences, using MacClade 4.08 (Maddison & Maddison 2000).
The first intron sequences of the S7 gene were compared to the sequence of Petrocephalus bovei archived in
Genbank under the accession number AY124274. The alignment requires the presence of five different indels and
the final alignment comprises 522 positions.
Results
Petrocephalus leo sp. nov.
(Table 1, Figures 2 and 3)
http://zoobank.org/008688C1-B0E9-48E6-B4C5-8AABAF0D829F
Holotype. CUMV 95314 (male, 76.1 mm SL). Field no. JPF 06-012, Central African Republic, Basse-Kotto,
Kotto River at Mingala, Kotto-Oubangui province (5.10N, 21.82E), collectors: R. Bills, J. P. Friel & D. Reid, 2
March 2006.
Paratypes (34). CUMV 91853 17 specimens, same locality, collector and date as the holotype (DNA tissues
590 and 595). MRAC 2016-012-P-00001-00003 three specimens, same locality, collector and date as the
holotype. AMNH 264802 three specimens, same locality, collector and date as the holotype. CUMV 91854 11
specimens. Field no. JPF 06-014, Central African Republic, Basse-Kotto, Rapids on Kotto River north of Mingala,
Kotto/Oubangui (5.27N, 21.89E), R. Bills, J. P. Friel & D. Reid , 3 March 2006.
Diagnosis. Petrocephalus leo sp. nov. is distinguished from all other Petrocephalus species of Central Africa
(i.e., Lower Guinea and Congo ichthyofaunal provinces) by the following combination of characteristics: absence
of electoreceptive rosettes on head, body coloration brownish with distinct black mark at the base of pectoral fin,
but no subdorsal ovoid black mark; 21 to 24 branched dorsal-fin rays (mean = 22) and 26 to 29 branched anal-fin
rays (mean = 27).
Description. Morphometric ratios and meristic data for holotype and paratypes are presented in Table 1.
Petrocephalus leo sp. nov. is a small-sized species within the genus (maximum SL observed = 78.9 mm; holotype
= 76.1 mm). Body ovoid, 2.9–3.4 times longer than high (paratype average = 3.2, holotype = 3.3) and laterally
compressed. Head length between 3.1 and 3.7 times in standard length (paratype average = 3.5, holotype = 3.6).
Snout short (5.2 ≤ HL/SNL ≤ 7.4, paratype average = 5.9, holotype = 6.0) and round. Mouth small (3.8 ≤ HL/MW
≤ 4.9, paratype average = 4.2, holotype = 3.8), sub-terminal, opening under posterior half of eye. Teeth small and
bicuspid, 7–9 in a single row in the upper jaw (paratype median = 8, holotype = 8), 15–23 in a single row in lower
jaw (paratype median = 18, holotype = 18). Dorsal and anal fins originate in posterior half of body (1.5 ≤ SL/PDD
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≤ 1.6 and 1.6 ≤ SL/PAD ≤ 1.7, respectively). Pre-dorsal distance slightly greater than pre-anal distance (1.0 ≤ PDD/
PAD ≤ 1.1). Dorsal fin with 21–24 branched rays (paratype median = 22, holotype = 22). Anal fin with 26–29
branched rays (paratype median = 27, holotype = 27). Body scaled except for head. Lateral line visible and
complete with 34–38 (paratype median = 36, holotype = 37) pored scales along its length. Twelve scales around
caudal peduncle. Nine to 12 scales (paratype average = 10, holotype = 9) between anterior base of anal fin and
lateral line. Caudal peduncle thin (1.9 ≤ CPL/CPD ≤ 2.5, paratype average = 2.2, holotype = 2.2). Twelve scales
around caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans visible, but not
clustered into the three distinct rosettes as described in Harder (1968).
TABLE 1 . Principal morphometric ratios and meristic counts for the holotype (CUMV 95314) and 34 paratypes [CUMV
91853(17), MRAC 2016-012-P-00001-00003(3), AMNH 264802(3), CUMV 91854(11)] of Petrocephalus leo sp. nov.
(Abbreviations: m= male; Std-Dev= standard deviation; Min-Max= minimum-maximum).
Holotype (m) Paratypes (n=34)
Min–Max Mean Std-Dev
Standard length (SL, in mm) 76.1 50.5–78.9 67.9 6.6
Head length (HL, in mm) 23.0 14.8–22.9 19.5 1.7
Ratio of standard length (SL):
SL/body height (H) 3.3 2.9–3.4 3.2 0.1
SL/head length (HL) 3.6 3.1–3.7 3.5 0.1
SL/pre-dorsal distance (PDD) 1.6 1.5–1.6 1.6 0.0
SL/pre-anal distance (PAD) 1.7 1.6–1.7 1.6 0.0
SL/dorsal fin length (DFL) 4.6 4.4–5.0 4.6 0.1
SL/anal fin length (AFL) 3.7 3.5–4.0 3.8 0.1
SL/caudal peduncle length (CPL) 6.4 5.7–6.8 6.4 0.3
SL/mouth width (MW) 13.7 13.4–17.1 14.7 0.9
Ratio of head length (HL):
HL/snout length (SNL) 6.0 5.2–7.4 5.9 0.5
HL/mouth width (MW) 3.8 3.8–4.9 4.2 0.3
HL/eye diameter (ED) 3.7 3.7–4.4 4.0 0.2
HL/interorbital width (IOW) 3.2 2.7–3.6 3.2 0.2
HL/head width (HW) 1.9 1.8–2.0 1.9 0.0
HL/mouth position (MP) 3.4 3.2–4.2 3.5 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.2 1.9–2.5 2.2 0.1
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 22 21–24 22
Anal fin branched rays (AR) 27 26–29 27
Number of scales in the lateral line (SLL) 37 34–38 36
Number of scale rows between the anterior
base of the anal fin and the lateral line (SDL)
991210
Number of teeth in the upper jaw (TUJ) 8 7–9 8
Number of teeth in the lower jaw (TLJ) 18 15–23 18
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FIGURE 2. Petrocephalus leo sp. nov. and Petrocephalus zakoni from the Oubangui River basin, Central African Republic.
Top, photograph of a live specimen of Petrocephalus leo sp. nov. of about 70 mm standard length showing the live coloration
(untagged specimen; photo by Roger Bills, SAIAB). Center, photograph of the preserved holotype of Petrocephalus leo sp.
nov. (CU 95314, scale bar = 1.0 cm; photo by John P. Sullivan, CUMV). Bottom, photograph of a preserved specimen of
Petrocephalus zakoni of about 70 mm standard length from the Oubangui River (Field station JPF 06-009, CU 91852; photo by
John P. Sullivan, CUMV).
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FIGURE 3. Schematic drawing of Petrocephalus leo sp. nov., holotype, 76.1 mm standard length. Drawn by Yi-Hsuan Lin.
Absence of the three typical Petrocephalus electroreceptive rosettes on the head distinguish P. l e o sp. nov.
from most of its congeners. Only four other species of Petrocephalus lack all three electoreceptive rosettes:
Petrocephalus microphthalmus, Petrocephalus haullevillii, Petrocephalus schoutedeni Poll 1954, and
Petrocephalus zakoni. Petrocephalus leo sp. nov. can be easily distinguished from these species (and all other
species of Petrocephalus) by its unique pattern of melanin markings: a distinct black spot at the origin of the
pectoral fins but no subdorsal pigmentation mark. Petrocephalus microphthalmus, P. haullevillii, and P.
schoutedeni lack a black mark at the origin of the pectoral fins and P. z a k o n i possesses a distinct subdorsal
pigmentation mark below the anterior base of the dorsal fin which often extends onto the first dorsal rays and
makes contact over the dorsum with the contralateral mark (Figure 2; Lavoué et al. 2010). Petrocephalus leo sp.
nov. can be further distinguished from Petrocephalus zakoni by its slender body (SL/H= 2.9-3.4, mean= 3.2;
holotype=3.3 versus 2.5-2.7 [mean = 2.6] in P. zakoni); its relatively shorter dorsal fin (SL/DFL= 4.4-5.0, mean=
4.6; holotype=4.6 versus 4.0-4.3 [mean = 4.1] in P. zakoni) and its smaller eye (HL/ED= 3.7-4.4, mean= 4.0;
holotype=3.7 versus 3.1-3.3 [mean = 3.2] in P. z a k on i ). Petrocephalus leo sp. nov. can be further distinguished
from P. microphthalmus, P. haullevillii, and P. schoutedeni, by a higher dorsal-fin ray count (range= 21-24, mean
and holotype = 22 versus <20 in P. microphthalmus, P. haullevillii, and P. schoutedeni).
Live coloration (Figure 2). Body background brown/copper with metallic reflection on flanks, darker dorsally
with belly whitish/silver with many dense melanophores visible. Caudal peduncle darker and lower margin of
dorsal and anal fins blackish. A distinct black mark at base of the pectoral fins and a crescent-shaped mark at base
of the caudal fin extending onto upper and lower lobes of caudal fin. All fins mostly whitish-brownish and
translucent, anterior of dorsal fin darker. Eye black.
Distribution (Figure 1). Petrocephalus leo sp. nov. is only known from two adjacent localities along the
course of the Kotto River (Oubangui River basin).
Electric organ discharge. Unknown. Electrocyte anatomy not studied; all Petrocephalus species examined
have electric organ of type "NPp" (Lavoué et al. 2008).
Etymology. This species is named after my son Léo (Latin name leo).
Additional records from the Oubangui River basin
Petrocephalus mbossou Lavoué, Sullivan and Arnegard, 2010
CUMV 91855 (one specimen: sexually mature male, 67.8 mm SL). Field no. JPF 06-017 (Figure 1), Central
African Republic, Ouaka, Liwa River Ouaka/Oubangui (5.67N, 20.69E), R. Bills, J. P. Friel & D. Reid, 4 March
2006.
CUMV 91859 (nine specimens: four sexually mature males and five individuals of indeterminate sex, 67.6–
91.1 mm SL). Field no. JPF 06-031 (Figure 1), Central African Republic, Ombella-Mpoko, Oubangui River
upriver from Bangui (4.38N, 18.72E), R. Bills, J. P. Friel & D. Reid, 14 March 2006 (DNA tissues 755 and 769).
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Remark: Previously only known from its holotype collected in Odzala-Kokua National Park, in the
northwestern part of the Congo River basin (Lavoué et al. 2010). Table 2 summarizes the main morphometric
ratios and meristic data for the Oubangui specimens, which differ from the holotype only by slightly shorter anal
and caudal fins and a slightly smaller interorbital width. As the holotype is far larger than any of the Oubangui
specimens, the slight observed differences may be due to allometry.
TABLE 2. Principal morphometric ratios and meristic counts for the holotype (CUMV [ex. CU] 92389) and 10
specimens from Oubangui [CUMV 91855(1), CUMV 91859(9)] of Petrocephalus mbossou; Std-Dev= standard
deviation; Min–Max= minimum–maximum).
Holotype
from Odzala
Specimens from Oubangui
(n=10)
Min
Max Mean Std-Dev
Standard length (in mm) 127.1 67.6
91.1 75.7 8.1
Head length (in mm) 36.9 19.4
26.1 21.8 2.4
Ratio of standard length (SL):
SL/body height (H) 3.0 2.6
3.0 2.8 0.1
SL/head length (HL) 3.4 3.3
3.6 3.5 0.1
SL/pre
-
dorsal distance (PDD) 1.7 1.5
1.7 1.6 0.0
SL/pre-anal distance (PAD) 1.6 1.5
1.7 1.6 0.1
SL/dorsal fin length (DFL) 4.4 4.1
4.4 4.2 0.1
SL/anal fin length (AFL) 4.3 3.5
3.8 3.6 0.1
SL/caudal peduncle length (CPL) 5.2 5.5
6.4 5.8 0.2
SL/mouth width (MW) 16.2 14.5
17.9 16.1 1.1
Ratio of head length (HL):
HL/snout length (SNL) 5.4 5.2
7.2 6.0 0.6
HL/mouth width (MW) 4.7 4.2
5.1 4.7 0.3
HL/eye diameter (ED) 3.7 3.3
3.8 3.6 0.2
HL/interorbital width (IOW) 4.3 3.0
3.6 3.3 0.2
HL/head width (HW) 2.2 1.8
2.0 1.9 0.1
HL/mouth position (MP) 2.8 2.8
3.4 3.0 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.9 2.3
2.9 2.6 0.2
Min
Max Median
Meristic counts:
Dorsal fin branched rays (DR) 24 22
24 23
Anal fin branched rays (AR) 26 26
28 26
Number of scales in the lateral line (SLL) 37 35
37 36
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
11 11
13 12
Number of teeth in the upper jaw (TUJ) 12 9
11 10
Number of teeth in the lower jaw (TLJ) 14 17
22 20
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A NEW SPECIES OF PETROCEPHALUS
Petrocephalus zakoni Lavoué, Sullivan and Arnegard, 2010
CUMV 91858 (two specimens, one examined). Field no. JPF 06-030 (Figure 1), Central African Republic,
Ombella-Mpoko, Oubangui River upriver from Bangui (4.38N, 18.72E), R. Bills, J. P. Friel & D. Reid, 13 March
2006.
CUMV 91852 (three specimens, two examined, Figure 2). Field no. JPF 06-009 (Figure 1), Central African
Republic, Basse-Kotto, Oubangui River downriver from Mobaye Oubangui River (4.33N, 21.15E), R. Bills, J. P.
Friel & D. Reid, 28 February 2006 (DNA tissue 549).
CUMV 91847 (one very small specimen, morphology not examined but cytochrome b nucleotide sequence
determined). Field no. JPF 06-002 (Figure 1), Central African Republic, Ouaka, Mbourou River at AXMIN
Ndassima mine camp Ouaka/Oubangui (6.16N, 20.80E), R. Bills, J. P. Friel & D. Reid, 23 February 2006 (DNA
tissue 442)
Petrocephalus christyi Boulenger, 1920
CUMV 95317 (two specimens, 68.1 and 60.6 mm SL). Field no. JPF 06-030 (Figure 1), Central African
Republic, Ombella-Mpoko, Oubangui River upriver from Bangui (4.38N, 18.72E), R. Bills, J. P. Friel & D. Reid,
13 March 2006.
Petrocephalus pulsivertens Lavoué, Sullivan and Arnegard, 2010
CUMV 95313 (one specimen). Field no. JPF 06-030 (Figure 1), Central African Republic, Ombella-Mpoko,
Oubangui River upriver from Bangui (4.38N, 18.72E), R. Bills, J. P. Friel & D. Reid, 13 March 2006.
Discussion
First case of conflict between morphology and genetic data in Petrocephalus. Petrocephalus leo sp. nov. is
easily distinguished from P. z a k o n i by several morphological characteristics, most notably the difference in color
pattern with the absence of a subdorsal mark (versus presence in P. z a k o n i ; Figure 2). Given this significant
morphological difference, finding the two cytochrome b haplotypes of P. leo sp. nov to be nested within the
haplotypes of P. z a k o n i (Figure 4A and B) was unexpected. The cytochrome b result suggests that P. zakoni may
not be monophyletic with respect to P. l e o sp. nov. However, phylogenetic analysis of the intron of the nuclear S7
gene (Figure 4C) unambiguously resolves this conflict by supporting the reciprocal monophyly of P. l e o sp. nov.
and P. zakoni. Such cases of incongruence at the species level between morphological and mitochondrial data are
common in fishes and, in particular, they are reported in the sister group of Petrocephalus, the subfamily
Mormyrinae. The most striking example in this subfamily is provided by the genus Paramormyrops that is mostly
restricted to the Lower Guinea province (Sullivan et al. 2002, 2004). Sullivan et al. (2002) used the cytochrome b
gene to reconstruct the phylogeny among Paramormyrops species; each putative species [considered as OTU by
these authors] could first be diagnosed by their electric organ discharge waveforms and their overall external
morphology. However, the cytochrome b-based phylogenetic tree only partially matched their predictions, as
several OTUs were found not monophyletic (Sullivan et al. 2002). To test the hypothesis that the mitochondrial
phylogeny incorrectly reflected species boundaries, Sullivan et al. (2004) surveyed the entire genome using
characters generated by the AFLP technique (Vos et al. 1995). Sullivan et al. (2004) showed that the AFLP-
generated characters supported a tree in which each phenotypic species was monophyletic.
Two commonly provided reasons for why individual gene-based phylogenetic tree reconstruction fails to
retrieve species as monophyletic are (1) the incomplete sorting of ancestral genetic polymorphisms or (2)
hybridization followed by gene introgression. The incomplete lineage sorting hypothesis postulates that the
cytochrome b haplotypes of P. z a k o n i diverged before the separation of P. zakoni with P. l e o sp. nov., whereas
under the hybridization-introgression hypothesis, the ancestor of the cytochrome b haplotypes of P. l e o sp. nov.
was acquired by past introgressive hybridization between P. l e o sp. nov. and the P. z a k o ni lineage sampled from
Yangambi, D.R. Congo. To test these two, mutually non-exclusive, hypotheses will require the examination of
more loci and more specimens.
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FIGURE 4. A) The 13 parsimony-informative positions from the cytochrome b sequences of seven specimens of
Petrocephalus zakoni from three Congolese ecoregions: the Sangha Ecoregion (at the Odzala-Kokua National Park); the
Cuvette Centrale Ecoregion (at Yangambi); and Sudanic Congo-Oubangui Ecoregion (at Ouaka and Oubangui Rivers) and two
specimens of Petrocephalus leo sp. nov. from the Kotto River (Sudanic Congo-Oubangui region). The base at each cytochrome
b position is indicated. B) The most parsimonious tree of Petrocephalus zakoni and Petrocephalus leo cytochrome b haplotypes
with branch lengths proportional to the number of substitutions (scale = one change). Tree rooted at the midpoint. C) The most
parsimonious tree of Petrocephalus zakoni and Petrocephalus leo S7 first introns; only nucleotide indels (and their positions)
are mapped: triangles indicate deletions and inverted triangles indicate insertions; tree rooted with Petrocephalus bovei
sequence from Genbank.
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A NEW SPECIES OF PETROCEPHALUS
Diversity of Petrocephalus of the Oubangui basin. The recent collection of Petrocephalus made by Roger
Bills, John Friel and Duncan Reid from the Oubangui region in 2006 contains one new species, P. leo sp. nov., and
three new species records for the region: P. pulsivertens, P. z ak on i and P. mbossou. Prior to this work, eight species
of Petrocephalus were known from the entire Oubangui River basin including the Uele drainage (Boulenger 1913;
Gosse 1968; Pellegrin 1920). With this work, the species count is brought to 12, with two of them being endemic to
the Oubangui region (P. l e o sp. nov. and P. h u t e r e a u i ). The other ten species occur elsewhere in the Congo River
drainage (Lavoué et al. 2010). Given the large size of the Oubangui region, its habitat diversity and the absence of
physical barriers between its lower basin and the central Congo basin, further collections are likely to include
additional Petrocephalus species widespread Congo basin, yet unreported from the Oubangui such as
Petrocephalus valentini Lavoué et al. 2010, Petrocephalus odzalaensis Lavoué et al. 2010 and Petrocephalus
arnegardi Lavoué & Sullivan 2014.
Acknowledgments
Petrocephalus specimens from the Oubangui region examined in this study were collected and transported by
Roger Bills, John P. Friel and Duncan T. Reid with funding from The All Catfish Species Inventory (NSF DEB-
0315963), under SAIAB permits with John P. Friel as designated agent. I am particularly grateful to John P. Friel,
John P. Sullivan and Charles Dardia (Cornell University Museum of Vertebrates, Ithaca, NY, USA) and Oliver
Crimmen and James Maclaine (Natural History Museum, London, UK) for access to the collections under their
care. Miguel Parrent (Royal Museum for Central Africa, Tervuren, Belgium) and Barbara Brown (American
Museum of Natural History, New York) provided curatorial assistance. The specimen photographs are credited to
Roger Bills and John P. Sullivan. The drawing shown in Figure 3 was made by Yi-Hsuan Lin. This work was
completed while I was supported by research grants (MOST103-2811-M-002-154 and MOST103-2119-M-002-
019-MY3) from Ministry of Science and Technology of Taiwan.
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... We obtained habitat data for all 261 valid species of Gymnotiformes and 199/234 (85.0%) valid species of Mormyroidea from museum collection records and published literature reports (Corbet 1961, Greenwood 1966, Ita 1978, Banister & Bailey 1979, Møller et al. 1979, Balon & Stewart 1983, Gosse 1984, Lévêque et al. 1991, Bailey 1994, Paugy et al. 1994, Kirschbaum 1995, Sanyanga et al. 1995, Ikomi 1996, van der Bank & Kramer 1996, Bigorne 2003a, Bigorne 2003b, Seegers et al. 2003, Lavoué et al. 2004, Sullivan & Hopkins 2005, Konan et al. 2006, Hopkins et al. 2007, Albert & Reis 2011, Lavoué 2011, Lavoué 2012, Kramer 2013, Monsembula Iyaba et al. 2013, Lavoué & Sullivan 2014, Lamanna et al. 2016, Lavoué 2016, Sullivan et al. 2016, Rich et al. 2017, Albert et al. 2020, Mulelenu et al. 2020, Fricke et al. 2021. We used primary literature when available for all species, but there is more primary literature available for Gymnotiformes than Mormyroidea. ...
... We obtained habitat data for all 261 valid species of Gymnotiformes and 199/234 (85.0%) valid species of Mormyroidea from museum collection records and published literature reports (Corbet 1961, Greenwood 1966, Ita 1978, Banister & Bailey 1979, Møller et al. 1979, Balon & Stewart 1983, Gosse 1984, Lévêque et al. 1991, Bailey 1994, Paugy et al. 1994, Kirschbaum 1995, Sanyanga et al. 1995, Ikomi 1996, van der Bank & Kramer 1996, Bigorne 2003a, Bigorne 2003b, Seegers et al. 2003, Lavoué et al. 2004, Sullivan & Hopkins 2005, Konan et al. 2006, Hopkins et al. 2007, Albert & Reis 2011, Lavoué 2011, Lavoué 2012, Kramer 2013, Monsembula Iyaba et al. 2013, Lavoué & Sullivan 2014, Lamanna et al. 2016, Lavoué 2016, Sullivan et al. 2016, Rich et al. 2017, Albert et al. 2020, Mulelenu et al. 2020, Fricke et al. 2021. We used primary literature when available for all species, but there is more primary literature available for Gymnotiformes than Mormyroidea. ...
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... The genus Marcusenius Gill 1862 contains 44 valid species (Decru et al., 2019;Fricke et al., 2019;Kisekelwa et al., 2016) and is the second largest genus of the Mormyridae, after Petrocephalus Marcusen 1854 which contains 47 species (Fricke et al., 2019;Lavoué, 2016). It occurs from the Nilo-Sudan region (Boden et al., 1997) to the Mhlatuze River system in South Africa (Kramer et al., 2007). ...
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