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Copyright © American Museum of Natural History 2023 ISSN 0003-0082
AMERICAN MUSEUM NOVITATES
Number 3999, 22 pp. May 18, 2023
Description of two new Labeo (Labeoninae;
Cyprinidae) endemic to the Lulua River in the
Democratic Republic of Congo (Kasai ecoregion);
a hotspot of sh diversity in the Congo basin
TOBIT L.D. LIYANDJA1 AND MELANIE L.J. STIASSNY2
ABSTRACT
Labeo mbimbii, n. sp., and Labeo manasseeae, n. sp., two small-bodied Labeo species, are
described from the lower and middle reaches of the Lulua River (Kasai ecoregion, Congo basin)
in the Democratic Republic of Congo. e two new species are members of the L. forskalii species
group and are genetically distinct from all other species of that clade. Morphologically they can
be distinguished from central African L. forskalii group congeners except L. dhonti, L. lukulae, L.
luluae, L. parvus, L. quadribarbis, and L. simpsoni in the possession of 29 or fewer (vs. 30 or more)
vertebrae and from those congeners by a wider interpectoral, among other features.
e two new species are endemic to the Lulua River and, although overlapping in geographi-
cal range and most meristic and morphometric measures, are readily dierentiated by diering
numbers of fully developed supraneural bones, predorsal vertebrae, snout morphology, and addi-
tional osteological features. e description of these two species brings the total of Labeo species
endemic to the Lulua basin to three. e third endemic species, L. luluae, was previously known
only from the juvenile holotype, but numerous additional specimens have now been identied.
e cooccurrence of 14 Labeo species in the Lulua River, three of which are endemic, highlights
this system as a hotspot of Labeo diversity in the Congo basin and across the continent.
1 Richard Gilder Graduate School, American Museum of Natural History; Department of Ichthyology, Ameri-
can Museum of Natural History; and Département de Biologie, Faculté des Sciences, Université de Kinshasa,
Kinshasa, Democratic Republic of Congo.
2 Richard Gilder Graduate School, American Museum of Natural History; Department of Ichthyology, Ameri-
can Museum of Natural History.
2 AMERICAN MUSEUM NOVITATES NO. 3999
INTRODUCTION
With 108 species currently recognized (Fricke et al., 2022; Froese and Pauly, 2022) Labeo is
the second most diverse genus in the cyprinid subfamily Labeoninae, and is widely distributed
throughout Africa and southeast Asia. e highest diversity is found in Africa and, based on
morphometric and anatomical features, Reid (1985) divided the 80+ African Labeo into six spe-
cies groups: L. coubie group, L. forskalii group, L. gregorii group, L. macrostoma group, L. niloticus
group, and L. umbratus group. Among these the L. forskalii group is by far the most species rich
and, with the exclusion of L. alluaudi, forms a monophyletic group (Lowenstein et al., 2011;
Liyandja, 2018; Liyandja et al., 2022) comprising over a third of the species currently recognized
in the Congo basin (Van Steenberge et al., 2016; Liyandja et al., 2022). However, because of wide-
spread convergent morphological evolution, the taxonomy of many members of the L. forskalii
group is problematical and remains a persistant impediment to sustainable resource management
of these important shes for subsistence sheries (Liyandja et al., 2022).
A recent study (Mbimbi et al., 2021) has highlighted the Lulua River, a large right-bank
tributary of the Kasai River (g. 1), as harboring one of the most species-rich sh communities
within the entire Congo basin. e Lulua basin is characterized by high geomorphological and
hydrological complexity (Roberts et al., 2015) resulting in a wide range of disjunct habitats
including numerous rapids and falls, pools, oodplains, and perennial and permanent swamps
located within a dense river network of some 71,400 km2 (Mbimbi et al., 2021). e Lulua
ichthyofauna is rich in cyprinids, and most notable is the cooccurence in the basin of an esti-
mated 14 Labeo species (Mbimbi et al., 2021: table A2), rendering the river a potential hotspot
of diversity for Labeo within the entire Congo basin. In a study of cryptic diversity within the
L. forskalii group incorporating both morphological and molecular data, Liyandja et al. (2022)
addressed some taxonomic issues highlighted by Mbimbi et al. (2021) but also recognized a
number of undescribed lineages of Labeo represented among specimens from the Lulua basin
and across central Africa. Despite the morphology-based revisionary works of Tshibwabwa
(1997) and Reid (1985), the taxonomy and species limits of many of these Labeo remain prob-
lematical (Van Steenberge et al., 2016), and an integrative approach is necessary for better taxo-
nomic resolution.
Liyandja et al. (2022) provided a necessary phylogenetic framework for taxonomic descrip-
tions for the numerous previously unrecognized L. forskalli group members in central Africa.
Here, in the rst of a series of studies aimed at rectifying this taxonomic impediment, we integrate
the results of the molecular phylogenetic analyses of Liyandja et al. (2022) with 2D geometric
morphometrics, traditional linear measures, meristics, and osteological features to provide formal
taxonomic descriptions for two new Labeo species; L. mbimbii, n. sp., and L. manasseeae, n. sp.
MATERIAL AND METHODS
S P: Fishes were collected and euthanized in accordance with
the guidelines for the use of shes in research (Jenkins et al., 2014) and ethical considerations
for eld research (Bennett et al., 2016). e holotypes and some paratypes of the two new spe-
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 3
cies were collected in the main channel of the Lulua River in September 2014. Topotypes of L.
lukulae were collected during a 2018 expedition to the Lukula River (Lukula, Kongo Central,
D.R.C.). All specimens were collected using gill-, cast-, and dip-netting techniques, and eutha-
nized using MS-222. Samples were provisionally grouped to species using conspicuous mor-
phological features and color patterns, photographed, and preserved in 10% formalin. Prior to
preservation, n clips were taken from 3 to 4 individuals per putative species and preserved in
cryotubes containing 95% ethanol.
Additional voucher specimens and comparative materials were obtained from collections
of the American Museum of Natural History (AMNH), the Academy of Natural Sciences of
Drexel University (ANSP), Auburn University Museum of Natural History (AUM), the Bavar-
ian State Collection of Zoology (ZSM), Cornell University Museum of Vertebrates (CUMV or
CU), and Oregon State University Ichthyology Collection (OS). Other abbreviations are AMCC,
Ambrose Monell Cryo Collection of the American Museum of Natural History; BD, body
depth; CT, micro-CT scanned specimens; HL, head length; SL, standard length.
C M E: A total of 120 specimens were included in our analy-
ses. In addition to 32 specimens of the new species (26 L. mbimbii, n. sp., and 6 L. manasseeae,
n. sp.), 88 other specimens were included (number of individuals examined in parenthesis): L.
annectens (8); OS 20622 (1), OS 21441 (1), OS 21320 (6). L. dhonti (6); AMNH 271056 (4), CU
95264 (2). L. lukulae (16); AMNH 276342 (7 topotypes), AMNH 276343 (6 topotypes), AMNH
FIGURE 1. A. Longitudinal profile of the Lulua River indicating subdivision into three sections based
on channel slope gradient (after Mbimbi et al., 2021). B. Lulua River basin showing collection localities
of the two new species (arrows indicate type localities). C. Location of the Congo basin, Kasai, Lulua,
and adjacent ecoregions.
4 AMERICAN MUSEUM NOVITATES NO. 3999
274961 (1), AMNH 274962 (1), ANSP 38553 (1). L. luluae (27); AMNH 243598 (9), AMNH
243599 (2), AMNH 247860 (3), AMNH 247970 (2), AMNH 247993 (2), AMNH 251177 (3),
AMNH 253469 (1), AMNH 269106 (2), AMNH 269108 (2), ANSP 51740 (holotype). L. parvus
(10); AMNH 276646 (1), AMNH 276647 (1), AMNH 278152 (1), CU 92141 (3 topotypes), CU
92147 (1 topotype), ZSM 42129 (3). L. quadribarbis (7); AMNH 253438 (1), AMNH 276667 (5),
AUM 51572 (1). L. simpsoni (14); AMNH 240995 (2), AMNH 243589 (1), AMNH 247071 (3),
AMNH 276658 (2), AMNH 276660 (1), AMNH 276663 (2), AUM 51572 (3).
M D C A: Genomic DNA was extracted from sev-
eral individuals of Labeo annectens, L. dhonti, L. lukulae, L. luluae, L. manasseeae, n. sp., L.
mbimbii, n. sp., L. parvus, L. polli, L. quadribarbis, and L. simpsoni from the Congo basin and
Lower Guinean ecoregions using the Qiagen Gentra Puregene Tissue Kit following the manu-
facturers protocol. A portion (652 bp) of the cytochrome oxidase subunit 1 (COI) and the
entire (1500 bp) recombination activate gene 1 (RAG1) were amplied and sequenced on a
Sanger sequencing platform following the protocol of Lowenstein et al. (2011). Additional
sequences were obtained from the Barcode of Life Data System (http://www.barcodinglife.org)
and GenBank (www.ncbi.nlm.nih.gov/genbank). Phylogenetic analyses were conducted using
both Bayesian inference (BI) and maximum likelihood (ML) as implemented respectively in
MrBayes 3.2.2 (Ronquist et al., 2012) and IQ-TREE (Nguyen et al., 2015). For full details of
molecular analytical methodology, see Liyandja et al. (2022).
M D C A: Specimens were photographed in
ventral and lateral (le side) views using a mounted Canon EOS 600D digital camera. Digital
images of Geometric Morphometric (GM) landmarks (g. 2), following Armbruster (2012),
were created using TpsUtil 1.70 (Rohlf, 2015) and TpsDig2 (Rohlf, 2015).
Twenty-six morphometric measurements and 18 meristic counts (tables 1 and 2) were
taken following Tshibwabwa and Teugels (1995) and slightly modied aer Tshibwabwa et
al. (2006), Moritz (2007), Moritz and Neumann (2017), and Armbruster (2012). Measure-
ments were made point to point, except for the caudal peduncle and postorbital length which
were measured as horizontal distances, using the linear measurement tool in TpsDig2 and
digital calipers, whereas scale counts were made under a stereomicroscope. Body depth was
measured as the vertical distance from the posterior insertion of the dorsal n to the ven-
trum. Radiograph images were used to count the total number of vertebrae, pleural ribs,
simple and branched dorsal and anal-n rays, procurrent and principal caudal-n rays. In
contrast to Tshibwabwa et al. (2006) and Tshibwabwa and Teugels (1995), all vertebrae pos-
sessing a hemal spine were counted as caudal vertebrae whereas those with ribs and with
hemal arches but lacking hemal spines were counted as abdominal vertebrae (Aguirre et al.,
2014). Circumpeduncular scales were counted at the narrowest point around the caudal
peduncle (Reid, 1985). Weberian vertebrae and the preural centrum were excluded from all
counts. Traditional morphometric and meristic data were analyzed separately in R (R Core
Team, 2013) using principal component analysis as implemented in the package FactoMineR
(Lê et al., 2008). Morphometric data were analyzed as log-transformed proportions of SL
with measurements of n lengths excluded (due to n damage). Invariant meristic counts
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 5
(simple dorsal-n rays, principal caudal-n rays, simple pelvic-n rays, branched pelvic-n
rays, and anal-n rays) were removed from subsequent analyses.
A minimum of ve representatives of each described species were CT-scanned at the
AMNH’s Microscopy and Imaging Facility (MIF), using either the nanofocus (180 kV/20 W)
or the microfocus (240 kV/320 W) tubes of a Phoenix V|tome|XS240 microCT scanner (Gen-
eral Electric, Faireld, CT) depending on specimen size. Specimens were scanned with a dia-
mond target at resolutions varying between 18.1 and 64.02 µm and a beam energy between
120–140 kV and 90–110 µA depending on specimen density. A total of 2500 projections per
specimen were collected for 400 ms each and averaged 3–4 times to improve signal-to-noise
ratios. Image reconstructions were conducted using the Phoenix datosjx (General Electric,
Wunstorf, Germany) soware and imported in Volume Graphics Studio Max 3.5.1 (Volume
Graphics, Heidelberg, Germany) for segmentation and visualization. Segmented anatomical
features were imaged in dierent views, with scale in Volume Graphics Studio Max 3.5.1 and
imported in TpsDig2 for linear measurement.
RESULTS
P R: Details of phylogenetic analyses and the resultant maxi-
mum-likelihood phylogram have been published and discussed in Liyandja et al. (2022). Labeo
mbimbii (as Labeo sp. ‘mbimbii’) and L. manasseeae (as Labeo sp. ‘Lulua’) are resolved as mem-
bers of a large, well-supported subclade of the L. forskalli group (subclade K of Liyandja et al.,
2022: g. 4), restricted almost entirely in geographical distribution to the Congo Basin, but
FIGURE 2. Homologous landmarks used in geometric morphometric analyses (following Armbruster, 2012):
A. lateral and B. ventral views.
6 AMERICAN MUSEUM NOVITATES NO. 3999
FIGURE 3. Simplied phylogram of subclade K modied aer Liyandja et al. (2022) showing placement of L.
mbimbii, n. sp., and L. manasseeae, n. sp. (in bold).
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 7
including two species (L. annectens and L. lukulae) from the southern portion of the adjacent
Lower Guinean ecoregion (Southern West Coastal Equatorial ecoregion of ieme et al., 2005).
Here, for ease of reference, we provide a simplied gure of subclade K indicating the phylo-
genetic placement of the two new species in relation to described species (g. 3). While the
study of Liyandja et al. (2022) was based on a limited molecular dataset (concatenated CO1
and RAG1 loci, 2023 bp), preliminary analysis of a genome-wide marker set (2600+ UCE loci,
>2,200,000 bp) with increased taxon sampling, supports a similar topology and corroborates
the monophyly of each species (Liyandja et al., in prep.).
As indicated in gure 3, L. mbimbii, n. sp., is sister to the L. sorex–L. nasus subclade, while
Labeo manasseeae, n. sp., belongs to the L. parvus subclade and, despite supercial resem-
blance, neither taxon is phylogenetically closely related to the poorly known Lulua River
endemic, L. luluae (Liyandja et al., 2022; see Discussion).
M: Aer the removal of invariant counts, two principal component analyses
(PCAs) were performed on the remaining counts. e rst was performed on all species for
13 meristic counts while the second was performed on 12 meristic counts including only those
species that were overlapping with L. manasseeae, n. sp., in the rst PCA. In that analysis,
79.25% of meristic variation is explained by the rst four principal components with PC1 and
PC2 accounting respectively for 33.7% and 22.9% of variation in the data. Dierences in scale
counts contributed most to the factor loadings of PC1, with the number of scales between the
lateral line and the dorsal n having the highest inuence (17.8%), whereas dierences in the
number of abdominal vertebrae (26.9%), pleural ribs (21.2%), total vertebrae (7.2%), and pro-
current dorsal-n rays (17.2%) contributed most to the loadings of PC2. PC1 divides these
species into two groups: L. annectens, L. dhonti, and L. lukulae with higher total lateral-line
scale counts, and higher counts between the lateral line and dorsal-n origin (35 or more and
4.5–5.5) versus L. luluae, L. manasseeae, n. sp., L. mbimbii, n. sp., L. parvus, L. quadribarbis, L.
simpsoni with fewer (35 or less and 4–4.5) (g. 4A). PC2 divides these species in two groups
as well, species (L. annectens, L. dhonti, and L. mbimbii, n. sp.) with higher abdominal vertebrae
counts (16–17) versus those (L. lukulae, L. luluae, L. manasseeae, n. sp., L. parvus, L. quadrib-
arbis, and L. simpsoni) with lower counts (14–15). In the scatter plot of these two principal
components L. mbimbii, n. sp., is clearly distinguished from the remaining species while L.
manasseeae, n. sp., overlaps with L. parvus, L. quadribarbis, L. simpsoni, and L. luluae. In the
second analysis the rst four principal components accounted for 62.7% of the data variation;
however, this analysis failed to separate these species from L. manasseeae, n. sp. (g. 4B), sug-
gesting that meristic features alone are unable to discriminate among these species.
M: A PCA was performed on 17 morphometric measurements aer
removal of n measurements (due to n damage) (g. 4C). e rst ve principal components
account for 71.1% of total variation with PC1, PC2, and PC3 accounting respectively for 26%,
15.1%, and 12.4% of variation. Dierences in the interpectoral width (14.6%), prepelvic length
(12%), vent–anal-n distance (10.3%), predorsal length (9.9%), head length (7.5%), and caudal
peduncle depth (6.8%) contributed the most to the factor loadings of PC1, whereas dierences
in the orbital length (19.5%), prepectoral length (15.4%), head length (14.8%), interorbital
8 AMERICAN MUSEUM NOVITATES NO. 3999
FIGURE 4. A. Scatterplot of PC2 against PC1 (PCA of 13 meristic counts for 120 specimens representative of
9 species). B. Scatterplot of PC2 against PC1 (PCA of 12 meristic counts for 44 specimens representative of
the ve species overlapping with L. manasseeae in A). C. Scatterplot of PC2 against PC1 (log-transformed
matrix, 12 morphometric measurements, for 114 specimens representative of 8 species).
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 9
width (10.2%), postorbital head length (8.1%), and caudal peduncle length (7.8%) contributed
the most in the loadings of PC2. PC1 divided these species into two main groups: L. mbimbii,
n. sp., L. manasseeae, n. sp., and L. luluae with shorter vent–anal-n distance (3.8%–6.9% SL)
versus L. lukulae, L. parvus, L. quadribarbis, and L. simpsoni with longer vent-anal n distance
(7.1%–11.4%SL). Although the scatter plot of PC1 vs PC2 (g. 4C) indicates separation there
is still some overlap.
Labeo mbimbii, new species
Figures 5, 6; table 1
Labeo cf. lukulae: Mbimbi et al., 2021
Labeo sp.‘mbimbii’: Liyandja et al., 2022
H: AMNH 277862 (AMCC 249232, CT), 91.5 mm SL, main channel of the Lulua
River over rocks at Dipumu Rapids, about 47 km downstream of Katende Dam, Kasai Central
Province, D.R. Congo, 05°56′12.4″S, 022°20′22.1″E, J.J. Mbimbi and T. Liyandja, September 2014.
P: AMNH 253456 (2, CT), 94.2–104.2 mm SL, main channel of the Lulua River
over rocks and rapids at Dijiba, about 19 km downstream of Katende dam, Kasai Central Prov-
ince, D.R.C., 06°10′21.8″S, 022°27′07.7″E, J.J. Mbimbi, July 2010; AMNH 269102 (2), 62.3–70.4
mm SL, main channel of the Lulua River over rocks at about 155 km in straight line upstream
of Katende Dam, Kasai Central Province, D.R.C., 07°44′21.7″S, 022°36′39.6″E, J.J. Mbimbi and
T. Liyandja, September 2014; AMNH 277863 (4, 2 CT), 81.5–93.8 mm SL, same locality as
holotype, J.J. Mbimbi and T. Liyandja, September 2014; AMNH 277864 (6, 1 CT), 62.0–71.6
mm SL, main channel of the Lulua River over rocks at Nsanga Nyembo Rapids, about 45.5 km
in a straight line downstream of Katende Dam, Kasai Central Province, D.R.C., 05°56′53.4″S,
022°20′29.4″E, J.J. Mbimbi, July 2008; AMNH 277865 (2), 81.3–84.5 mm SL, main channel of
the Lulua River over rocks downstream Nsanga Nyembo, about 47 km in a straight line down-
stream of Katende Dam, Kasai Central Province, D.R.C., 05°55′55.8″S, 022°20′27.6″E, J.J.
Mbimbi, July 2008; AMNH 277866 (3), 78.09–83.37 mm SL, same locality as AMNH 277864,
J.J. Mbimbi, July 2008; ANSP 208760 (1), 90.05 mm SL, main channel of Lulua River in rocky
habitat at about 2 km upstream of Dipumu Rapids, Kasai Central Province, D.R.C., 05°57′17.8″S,
022°20′43.3″E, J.J. Mbimbi and T. Liyandja, September 2014; ANSP 208761 (1), 80.6 mm SL,
main channel of the Lulua River over rocks at Katende Rapids, Kasai Central Province, D.R.C.,
06°20′37.2″S, 022°27′1.3″E, J.J. Mbimbi, January 2009; MRAC 2023.001.P.0001–0002 (2),
85.69– 92.68 mm SL, same locality as holotype, J.J. Mbimbi and T. Liyandja, September 2014;
ZSM 48369 (2), 94.67–103.6 mm SL, same locality as holotype, J.J. Mbimbi and T. Liyandja,
September 2014.
A N M: AMNH 269104 (11), 53.48–82.13 mm SL, same locality
as holotype, J.J. Mbimbi and T. Liyandja, September 2014.
D D: While no unambiguous morphological autapomorphies have
been located to diagnose Labeo mbimbii, the species is distinguished from all central African
10 AMERICAN MUSEUM NOVITATES NO. 3999
TABLE 1. Labeo mbimbii, n. sp., Morphometric measurements and meristic data for the holotype and 25
paratypes.
Holotype Holotype + Paratypes
Max Min Mean±SD
Morphometric measurements
Standard length (SL) (mm) 91.5 104.2 62.0
Body depth (mm) 16.4 19.3 11.1 15.5±2.2
Head length (mm) 24.2 27.8 16.1 21.8±3.0
Caudal peduncle length (mm) 10.2 13.4 7.3 10.3±1.4
% SL
Body depth (BD) 18 19.8 17.8 18.8±0.5
Caudal peduncle depth (CPD) 14.6 14.9 13.0 14.4±0.5
Head length (HL) 26.4 28.7 25.1 26.4±0.8
Predorsal length (PDL) 47.1 50.2 46.2 47.9±1.0
Preanal length (PAL) 82.4 84.7 78.4 81.4±1.8
Prepelvic length (PVL) 56.5 58.3 53.8 56.4±1.2
Prepectoral length (PPL) 27 28 24.3 26.2±1.1
Dorsal-n base (DFL) 21.1 26.5 19.2 22.0±1.4
Dorsal-n length (DRL) 24.9 26.9 22.6 24.8±1.2
Pectoral-n length (PL) 22 23.5 20.0 22.3±0.9
Pelvic-n length (VL) 20 21.4 18.1 19.8±0.8
Anal-n base (AL) 8.6 8.6 7.1 7.8±0.3
Anal-n length (ARL) 18.8 21.4 18.4 19.7±1.0
Vent–anal-n length (VAL) 5.6 6.7 4.1 5.7±0.7
Caudal peduncle length (CPL) 11.1 13.9 11.1 12.5±0.6
% HL
Snout length (SnL) 52.3 54.7 45.9 51.1±2.2
Interorbital width (IOW) 38.4 43.6 32.5 39.0±2.3
Internarial width (INW) 31.1 31.6 25.1 28.9±1.6
Bony orbital diameter (ED) 25.5 28.3 21.5 24.6±1.4
Postorbital length (POL) 25.6 33.8 24.9 27.8±2.0
%BD
Interpectoral width (IPW) 111.1 117.8 100.2 106.1±4.7
%CPL
Caudal peduncle depth (CPD) 131.3 131.3 101.0 115.9±7.3
Meristic counts Max Min Mode
Simple dorsal-n rays 3 3 3 3
Branched dorsal-n rays 9 10 9 10
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 11
Holotype Holotype + Paratypes
Max Min Mean±SD
Scales in lateral line 31+3 32+3 31+3 31+3
Scale rows between lateral line and dorsal n 4 4.5 4 4
Scale rows between lateral line and pelvic n 3 3.5 3 3
Circumpeduncular scales 12 12 12 12
Predorsal scales 9 10 9 9
Principal caudal-n rays 19 19 19 19
Upper procurrent caudal-n rays 9 9 8 8
Lower procurrent caudal-n rays 7 8 7 7
Simple pelvic-n rays 1 1 1 1
Branched pelvic-n rays 8 8 8 8
Simple anal-n rays 3 3 3 3
Branched anal-n rays 5 5 5 5
Total vertebrae 29 29 28 29
Abdominal vertebra 16 17 16 16
Caudal vertebra 13 13 12 13
Pleural ribs 13 14 12 13
L. forskalii group congeners except L. dhonti, L. lukulae, L. luluae, L. manasseeae, n. sp., L.
parvus, L. quadribarbis, and L. simpsoni in the possession of 28–29 vertebrae (vs. 30 or
more), and from all of these species in the possession of 5 (vs. 4) predorsal vertebrae, 4 (vs.
3) well-developed supraneural bones between the neural spines of the predorsal vertebrae,
and generally 3 (vs. 4) unbranched dorsal-n rays. It is further distinguished from L. manas-
seeae, n. sp., in the possession of a snout with a deep ethmoid furrow and well-developed
eshy appendage vs. a snout with a shallow ethmoid furrow and weakly developed eshy
appendage, and a robust, deep-keeled, thick-necked urohyal bone (vs. gracile, shallow keeled
with narrow neck).
D: Based on holotype and 25 paratypes. General appearance as in gure 5,
proportional measurements and meristic counts in table 1. Small-bodied species, maximum
observed size 104.2 mm SL (AMNH 253456), elongate, cylindriform, somewhat dorsoventrally
compressed (BD 17.8%–19.8% SL). Genital opening situated well in advance of anal-n origin,
vent–anal-n distance 4.1%–6.7% SL. Head moderately large, with slightly convex or attened
interorbital space. Snout broad and truncate, ethmoid furrow deep, well-developed eshy
appendage with few (ve to eight, generally ve) large tubercles. Eyes large, dorsolaterally
positioned, not visible in ventral view. Mouth large, inferior, lips plicate, anterior barbels absent,
posterior barbels small, deeply embedded in lip fold, not externally visible.
Dorsal n, iii 9 or 10 rays, margin slightly concave, inserted a little in front of midbody
(predorsal length 46.2%–50.2% SL), anal n, iii 5 rays. Caudal n emarginate, 8–9 upper, 7–8
TABLE 1 continued
Mode
12 AMERICAN MUSEUM NOVITATES NO. 3999
lower procurrent rays, 19 principal rays. Pectoral ns broad, inserted lateroventrally, interpec-
toral width 100.2%–117.8% BD. Pelvic ns, i8, slightly shorter than pectorals.
Scales cycloid, 31(21)–32(5) in lateral line to hypural joint; 4–4.5 between lateral line and
dorsal-n origin; 3–3.5 between lateral line and pelvic-n origin; 12 circumpeduncular. Total
vertebral count (exclusive of 4 Weberian centra and terminal preural centrum), 28–29 (mode
29), comprised of 16–17 (mode 16) abdominal and 12–13 (mode 13) caudal centra.
Some additional osteological features variable among African Labeo are presented in gure
6. e Weberian apparatus of L. mbimbii is relatively massive (g. 6A), with the anterior Webe-
rian supraneural (supraneural 3 following the nomenclature of Bird and Hernandez, 2007)
robust, 1.2× longer than tall, and in direct contact with the supraoccipital. No supraneural
between the neural spine of the fourth Weberian centrum and the neural spine of the rst
predorsal centrum. Four supraneural bones anterior to the neural spines of predorsal centra
2–5. Five predorsal vertebrae. Urohyal (g. 6B) robust, thick-necked, with a deep keel. Infra-
orbital series (g. 6C) consists of an elongate rst infraorbital (lachrymal) and four additional
elements, none of which are ventrally expanded or in contact with the preopercle.
C: Immediately postmortem (g. 5A) coloration varies from black to dark gray
or brown above, pale brown to whitish below, no dark lateral band visible either in adults or
juveniles. Preserved specimens (g. 5B–D) are dark brown above and paler brown below. A
dark lateral band is visible in preserved juveniles.
D: A Lulua River endemic, known from the main channel of the lower and
middle Lulua basin (g. 1).
B E: All specimens of L. mbimbii have been collected in rapids along the
Lulua River main channel over rocky substrates. ese observations, combined with a dorsoven-
trally compressed body shape, suggest that L. mbimbii is adapted to rapid, rocky main-channel
habitats. e waters where specimens have been collected are slightly acidic (pH 5.5–6.5), with
low conductivity (2–5 µS/cm2) and low concentrations of dissolved solids (TDS 4–10 ppm).
E: Labeo mbimbii is named for Prof. José Justin Mbimbi Mayi Munene (JJMMM)
of the Biology Department, College of Sciences, University of Kinshasa. JJMMM is the lead
FIGURE 5. Labeo mbimbii, n. sp. Holotype (AMNH 277862, AMCC 249232) in A. lateral view, immediately
postmortem; B. in preservation, lateral view; C. ventral view; and D. dorsal view. Scale bar = 1 cm.
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 13
FIGURE 6. Labeo mbimbii, n. sp. Holotype (AMNH 277862): CT scan renderings of A. posterior neurocra-
nium, Weberian apparatus and proximal axial elements; B. isolated urohyal bone; and C. infraorbital series.
Scale bars = 1 mm
14 AMERICAN MUSEUM NOVITATES NO. 3999
investigator and PI of the Lulua Project that has resulted in the deposition at the AMNH and
the University of Kinshasa, of more than 5000 specimens representing over 200 species, includ-
ing those described in the present paper. We dedicate this species to his outstanding work and
commitment to biodiscovery and conservation in the Kasai basin.
Labeo manasseeae, new species
Figures 7, 8; table 2
Labeo sp. nov.: Mbimbi et al., 2021
Labeo sp.‘Lulua’: Liyandja et al., 2022
H: AMNH 269110 (AMCC 249240, CT), 121.2 mm SL, main channel of the Lulua
River over rocks at Sandoa (Sanduwa), 0.05 km downstream of Sandoa Bridge, Lualaba Prov-
ince, D.R.C., 09°41′37.2″S, 022°51′30″E, J.J. Mbimbi and T. Liyandja, September 2014.
P: AMNH 269103 (AMCC 249230, CT), 97.3 mm SL, main channel of the Lulua
River in rocky and rapids habitat about 0.35 km downstream of crossing point on road to
Kapanga, Lualaba Province, D.R.C., 08º16′04.3″S, 022º35′50.2″E, J.J. Mbimbi and T. Liyandja,
September 2014; AMNH 277861 (AMCC 249238–9, 2, 2 CT), 52.88–70.46 mm SL, collected
with AMNH 269103; ZSM 48370 (2, 1 CT), 50.23–74.47 mm SL, Lukushi River (tributary of
Lulua) at Mukanda rapids, Lualaba Province, D.R.C., 10°30′25.4″S, 23°23′ 33.8″E, E. Vreven et
al., August 2012.
A N M: AMNH 247858, 1, 116.4 mm SL, main channel of the
Lulua River over rocks at Ntumba Shambuyi Rapids located 2.23 km downstream of Dipumu
Rapids, Kasai Central Province, D.R.C., J.J. Mbimbi, July 2008.
D D: While no unambiguous morphological autapomorphies have
been located to diagnose Labeo manasseeae the species is distinguished from all central African
L. forskalii group congeners except L. dhonti, L. lukulae, L. luluae, L. mbimbii, L. parvus, L.
quadribabrbis, and L. simpsoni in the possession of 28 vertebrae (vs. 30 or more). Labeo manas-
seeae is distinguished from L. lukulae, L. luluae, and L. quadribarbis by a larger interpectoral
width (94.7%–107.9% vs. 66.7%–92.8% BD), from L. parvus, L. quadribarbis, and L. simpsoni
by a shorter vent–anal-n distance (5.0%–6.9% vs. 11.4%–7.1% SL), and from L. dhonti and L.
lukulae in the possession of 30–31 (vs. 35–36) pored lateral-line scales. It is distinguished from
L. mbimbii in the possession of 3 fully developed supraneural bones (vs. 4), 4 predorsal verte-
brae (vs. 5), a pointed snout with a shallow ethmoid furrow and weakly developed eshy
appendage versus a truncate snout with a deep ethmoid furrow and well-developed eshy
appendage, and a gracile, narrow-necked, shallow-keeled (vs, robust, thick-necked, and deep-
keeled) urohyal bone.
D: Based on the holotype and ve paratypes. General appearance as in gure 7,
proportional measurements and meristic counts in table 2. Small-bodied species, maximum
observed size 121.2 mm SL (holotype), elongate, cylindriform, somewhat dorsoventrally com-
pressed (BD 16.1%–19.2% SL). Genital opening situated well in advance of anal-n origin, vent–
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 15
TABLE 2. Labeo manasseeae, n. sp., morphometric measurements and meristic data for the holotype and
ve paratypes.
Holotype Holotype + Paratypes
Max Min Mean±SD
Morphometric measurements
Standard length (mm) 121.2 121.2 50.2
Head length (mm) 31.5 31.5 14.3 22.3±6.8
Body depth (mm) 22.2 22.2 8.9 15.0±5.4
Caudal peduncle length (mm) 15.9 15.9 6.2 10.4±4.9
% SL
Body depth (BD) 18.3 19.2 16.1 17.5±1.2
Caudal peduncle depth (CPD) 13.7 14.7 12.1 13.2±1.0
Head length (HL) 26.0 28.9 26,0 26.7±1.0
Predorsal length (PDL) 44.8 48 44.8 46.5±1.1
Preanal length (PAL) 81.6 81.7 79.8 81.2±0.7
Prepelvic length (PVL) 56.2 59.6 56.2 57.2±1.2
Prepectoral length (PPL) 25.7 29.5 25.7 27.3±1.3
Dorsal-n base (DFL) 20.0 22.7 19.6 20.8±1.2
Dorsal-n length (DRL) 24.2 27.9 23.7 26.2±1.8
Pectoral-n length (PL) 20.5 21.8 18.9 20.7±1.0
Pelvic-n length (VL) 17.9 19.1 16.9 18.3±0.8
Anal-n base (AL) 7.5 8.5 7.3 7.7±0.4
Anal-n length (ARL) 18.8 19.2 16.9 18.5±0.8
Vent–anal-n length (VAL) 6.4 6.9 5.0 6.2±0.6
Caudal peduncle length (CPL) 13.1 13.4 11.7 12.5±0.6
% HL
Snout length (SnL) 52.1 51.5 45.5 48.5±2.4
Interorbital width (IOW) 36.2 39.1 33.3 35.6±2.5
Internarial width (INW) 27.5 30.1 23.7 26.4±2.7
Bony orbital diameter (ED) 24.3 28.2 19.8 24.2±2.9
Postorbital length (POL) 27.7 33.9 28.0 30.8±1.9
%BD
Interpectoral width (IPW) 101.3 107.9 94.7 101.3±4.3
%CPL
Caudal peduncle depth (CPD) 104.8 121.4 98.5 106.6±8.8
Meristic counts Max Min Mode
Simple dorsal-n rays 4 4 4 4
Branched dorsal-n rays 10 10 10 10
16 AMERICAN MUSEUM NOVITATES NO. 3999
Holotype Holotype + Paratypes
Max Min Mean±SD
Scales in lateral line 31+3 31+3 30+3 31+3
Scale rows between lateral line and
dorsal-n origin 4 4 4 4
Scale rows between lateral line and
pelvic-n origin 3 3 3 3
Circumpeduncular scales 12 13 12 12
Predorsal scales 9 10 8 9
Principal caudal-n rays 19 19 19 19
Upper procurrent caudal-n rays 8 8 8 8
Lower procurrent caudal-n rays 7 7 6 6
Simple pelvic-n rays 1 1 1 1
branched pelvic-n rays 8 8 8 8
Simple anal-n rays 3 3 3 3
Branched anal-n rays 5 5 5 5
Total vertebrae 28 28 28 28
Abdominal vertebra 15 16 15 15
Caudal vertebra 13 13 12 13
Pleural ribs 12 13 12 12
anal-n distance 5.0%–6.9% SL. Head moderately large, with slightly convex interorbital space.
Snout narrow and pointed, ethmoid furrow shallow, weakly developed eshy appendage bearing
8 or more small tubercles. Eyes large, dorsolaterally positioned, not visible in ventral view. Mouth
relatively small, inferior, lips plicate, anterior barbels small (absent in large specimens), posterior
barbels small, deeply embedded in lip fold, externally visible in small specimens.
Dorsal n, iv10 rays, margin slightly concave, inserted just anterior to midbody (predorsal
length 44.8%–48.0% SL), anal n iii5 rays. Caudal n strongly emarginate, 8 upper, 6–7 lower
procurrent rays, 19 principal rays. Pectoral ns broad, inserted lateroventrally, interpectoral
width 94.7%–107.9% BD. Pelvic ns, i8, slightly shorter than pectorals.
Scales cycloid, 30–31 in lateral line to hypural joint; 4 between lateral line and dorsal-n
origin; 3 between lateral line and pelvic-n origin; 12 circumpeduncular. Total vertebral count
(exclusive of 4 Weberian centra and the terminal preural centrum), 28, comprised of 15–16
(mode 15) abdominal and 12–13 (mode 13) caudal centra.
e Weberian apparatus of L. manasseeae is relatively massive (g. 8A), with anterior Weberian
supraneural 3 relatively gracile, 1.3× longer than tall, and in direct contact with the supraoccipital.
No supraneural between the neural spine of the fourth Weberian centrum and the neural spine of
the rst predorsal centrum. ree fully developed supraneural bones anterior to the neural spines
of predorsal centra 2–4 (a vestigial fourth supraneural bone is present in the holotype, but absent
TABLE 2 continued
Mode
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 17
in all other specimens). Four predorsal vertebrae. Urohyal (g. 8B) is gracile, thin necked, with a
shallow keel. Infraorbital series (g. 8C) consists of an elongated rst infraorbital (lachrymal) and
four additional elements, none of which are ventrally expanded or in contact with the preopercle.
C: Immediately postmortem (g. 7A) coloration varies from brown to dark
brown or black above, pale brown to cream below, a dark lateral band is barely visible at any
size. Preserved specimens (g. 7B–D) are dark brown above and brown below, and dark lateral
band is visible in most specimens.
D: A Lulua River endemic, Labeo manasseeae is known mainly from the mid-
dle basin, with single records from the lower and upper basins (g. 1). However, due to inac-
cessibility the upper Lulua has been poorly sampled (Mbimbi et al., 2021) and it is likely that
additional collecting eorts will expand the range of this species.
B E: Labeo manasseeae has been collected in rocky, rapids habitats in
the main channel of the middle Lulua, with one occurrence in a tributary of the upper basin.
As for L. mbimbii, L. manasseeae appears to be adapted to rocky, rapids habitats of both the
main channel and tributaries. e water in the main channel sites where L. manasseeae was
collected is slightly acidic (pH 5.5–6.5), has low conductivity (2–5 µS/cm2), and low concentra-
tion of dissolved solids (TDS 4–10 ppm).
E: Dedicated to Manassée W.E. Liyandja, the daughter of Tobit Liyandja. Manas-
sée was born a few months prior to the expedition that led to the discovery of this new species
and is an ongoing source of motivation for T.L.
DISCUSSION
Despite the extensive revisional work of Tshibwabwa (1997), species delimitation and
identication among African Labeo remains challenging. Van Steenberge et al. (2016) sug-
gested that one reason for the diculty in correctly identifying species of Labeo, particularly
in the Congo basin, is that many of the morphological characters traditionally used for spe-
cies identication are subject to considerable allometric and geographic variation. Liyandja
et al. (2022) concluded that in addition to these problems, pervasive convergent evolution
in body form and pigmentation patterning among L. forskalii group species has resulted in
FIGURE 7. Labeo manasseeae, n. sp. Holotype (AMNH 269110, AMCC 249240): A. immediately postmortem;
B. in preservation, lateral view; C. ventral view; and D. dorsal view. Scale bar = 1 cm
18 AMERICAN MUSEUM NOVITATES NO. 3999
FIGURE 8. Labeo manasseeae, n. sp. Holotype (AMNH 269110): CT scan renderings of A. posterior neuro-
cranium, Weberian apparatus and proximal axial elements; B. isolated urohyal bone; and C. infraorbital series.
Scale bars = 1 mm.
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 19
similar ecomorphs exhibited by distantly related species that overlap in most traditionally
employed meristic and morphometric measures. Recent genetic investigations have identi-
ed well-supported monophyletic species and species groups, but also have revealed high
levels of cryptic diversity with numerous previously unrecognized lineages and putative new
species (Lowenstein et al., 2011; Liyandja et al., 2022). Despite strong molecular support for
the recognition of many of these entities as distinct species (Liyandja et al., 2022; e.g., g. 4),
diagnostic morphological features are frustratingly elusive. Yet formal taxonomic and
nomenclatural recognition of such morphologically cryptic species is of central importance
for accurate biodiversity assessments, sustainable sheries management, and regional con-
servation eorts. Here we provide dierential diagnoses for two new species relying on com-
binations of meristic, morphometric measures, and osteological features, with the latter
unfortunately not visible from external examination. While we acknowledge the problematic
nature of such dierential diagnoses for eld identication, we believe that these diagnoses
will at least aid in the correct identication of museum-held specimens, and facilitate a more
accurate assessment of biological diversity in future studies.
Recently, Mbimbi et al. (2021) highlighted the exceptionally high diversity of the Lulua
River ichthyofauna, suggesting that this large tributary in the Kasai ecoregion harbors one of
the most species-rich sh communities in the entire Congo basin. Certainly, with the cooc-
curence of an estimated 14 species, the Lulua basin is outstanding in terms of Labeo diversity,
and unmatched as far as we can determine by any other region in the Congo basin or indeed
elsewhere across the continent. Despite these high species numbers, prior to the present study,
a single Labeo species was considered endemic to the Lulua River. at species is Labeo luluae,
a taxon described by Fowler (1930) based on a single juvenile, now in poor preservation (ANSP
51740, 30.4 mm SL, g. 9A) collected from the rapids of Katende (the site of a present-day
hydroelectric plant) in the lower portion of the Lulua Basin. Tshibwabwa (1997) reported a
second specimen that he identied as L. luluae from the Aruwimi River, at a site over 1000 km
northwest of Katende in the Uele ecoregion. Although, we have been unable to examine that
FIGURE 9. A. Labeo luluae, holotype (ANSP 51740). B. Labeo lugubris, holotype (AMNH 12334). Scale bars
= 1 cm.
20 AMERICAN MUSEUM NOVITATES NO. 3999
specimen, from Tshibabwa’s description and our own investigation of the holotype we conclude
that the Aruwimi specimen is not conspecic with L. luluae and its asignment remains uncer-
tain. However, based on detailed examination of the holotype and subsequent comparison of
CO1 sequences we tentitively identify numerous additional specimens from the lower Lulua
as L. luluae (see Comparative Materials Examined). However, as the preliminary phylogenetic
analyses of Liyandja et al. (2022) recovered two divergent groups among these putative L. luluae
samples, additional investigation of this potential complex will be necessary to determine
whether these specimens represent a single or multiple Lulua River endemics; a neccesary
prerequisite for a formal taxonomic redescription of L. luluae (Liyandja et al., in prep.). Paren-
thetically, we note that L. lugubris described by Nichols and LaMonte (1933) for a single speci-
men from Luluabourg (Kananga) in the lower Lulua basin has been synonymized with L.
chariensis (Reid, 1985; Tshibwabwa, 1997) a species originally described from the Chari River
not the Congo. However, examination of the holotype (AMNH 12334, g. 9B) suggests that L.
lugubris is morphologically closely related to specimens assigned here to the L. luluae complex.
We therefore consider the synonomy of L. lugubris with L. chariensis in error, however, nal
resolution of its correct placement must await further investigation of the L. luluae complex as
a whole. Regardless, the holotype of L. lugubris can readily be distiguished from both of the
new species described here by a longer vent–anal-n distance (10.4 vs. 6.9–4.1% SL). Addition-
ally, it diers from L. mbimbii by having fewer predorsal vertebrae (4 vs. 5), more small tuber-
cles over the eshy snout appendage, and the lack of a deep ethmoid furrow. Labeo lugubris is
further distinguished from L. manasseeae by total vertebral number (29 vs. 28), urohyal shape
(robust vs. gracile), number of upper procurent caudal-n rays (9 vs. 8), longer snout (65.6%
vs. 45.5–51.5% HL), deeper caudal peduncle (140.0% vs. 98.5%–121.4% CPL), and smaller
orbital diameter (15.1 vs. 19.8%–28.2% HL).
Regardless of the nal resolution of the species composition of L. luluae and subsequent
synonomy of L. lugubris, the current study brings the number of Labeo species endemic to this
single basin minimally to three, and strengthens the proposal of Mbimbi et al. (2021) that the
Lulua River may merit consideration as a separate ecoregion within the Kasai basin, and is one
in urgent need of renewed conservation attention.
ACKNOWLEDGMENTS
is research was funded by the Axelrod Research Curatorship (MLJS) and a graduate
fellowship from the Richard Gilder Graduate School of the American Museum of Natural His-
tory (TLDL). We are especially grateful to omas Vigliotta, Radford Arrindell, Chloe Lewis,
Morgan Chase, and Lauren Audi for technical assistance to TLDL during the realization of this
research. We also gratefully acknowledge Maxwell Bernt, Bruno Melo, and Naoko Kurata for
their companionship and advice, with especial thanks to Bruno Melo for insightful input on
an earlier version of this paper. We thank David Werneke and Jonathan W. Armbruster (AUM),
Casey Dillman (CUMV), Brian Sidlauskas (OS), Dirk Neumann (ZSM), and Mark H. Sabaj
(ANSP) for specimen loans, tissues gis, and sharing pictures of type specimens.
2023 LIYANDJA & STIASSNY: TWO NEW LABEO LABEONINAE; CYPRINIDAE 21
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