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. 2025 Apr 20;107(2):592–602. doi: 10.1111/jfb.70062

Hidden in plain view: A new Labeo (Cyprinidae: Labeoninae) endemic to the Kouilou‐Niari River basin in the Lower Guinea ichthyological province

Tobit L D Liyandja 1,2,3,✉, Melanie L J Stiassny 4
PMCID: PMC12360146  PMID: 40254807

Abstract

Labeo niariensis sp. nov., a small‐sized Labeo species, is described from the Kouilou‐Niari River system in the Lower Guinean ichthyofaunal province. The species is a member of the newly erected Labeo annectens species group. Morphologically, it is distinguished from all congeners by the presence of a deeply bifurcate posterior process of the kinethmoid. It further differs from all the described Lower Guinean Labeo, except L. annectens and Labeo nunensis, by possessing six (vs. five or fewer) pre‐dorsal vertebrae. The new species is further distinguished from L. annectens and L. nunensis by the presence of a prominent anterior notch and moderately developed posterior process on the first infraorbital (lachrymal) versus absence of an anterior notch and an elongated posterior process, presence of a deeply ovoid second infraorbital versus narrow and elongate, and by meristic and morphometric differences in body shape and proportions. L. niariensis is currently only known from the Kouilou‐Niari River system in the Republic of Congo.

Keywords: CT scan, Kouilou‐Niari River, Labeo, Labeo niariensis, morphometrics, taxonomy

1. INTRODUCTION

The genus Labeo, with about 110 valid species (Fricke et al., 2024; Froese & Pauly, 2024; Liyandja et al., 2022, Liyandja & Stiassny, 2023), is widely distributed throughout Sub‐Saharan Africa and Southeast Asia, with the greatest richness found in Africa (Lavoué, 2019). African Labeo were reviewed by Reid, (1985) who divided them into six species groups based on morphometric and anatomical characters: Labeo gregorii group, Labeo macrostoma group, Labeo umbratus group, Labeo niloticus group, Labeo coubie group and Labeo forskalii group; however, numerous molecular studies have shown these groups to be paraphyletic (Liyandja, 2018; Liyandja et al., 2022; Lowenstein et al., 2011). Most recently, based on a newly reconstructed phylogenomic hypothesis, Liyandja et al. (in review) reclassified African species of Labeo into nine species groups arrayed in three monophyletic subgenera. In that study, Labeo niariensis sp. nov. (designated Labeo sp. 2) was considered a member of the Labeo annectens group, which appears to be endemic to the Lower Guinean (LG) ichthyofaunal province.

The LG ichthyofaunal province constitutes one of the continent's diversity hotspots, characterized by high levels of endemism (Snoeks et al., 2011; Sonet et al., 2019). The province hosts over 580 brackish and freshwater fish species, including about 75 species of Cyprinidae (Mamonekene et al., 2018; Mipounga et al., 2019; Stiassny et al., 2007). However, among the many cyprinids reported from the LG are only six Labeo species: L. annectens Boulenger, 1903; Labeo batesii Boulenger, 1911; Labeo camerunensis Trewavas, 1974; Labeo lukulae Boulenger, 1902; Labeo nunensis Pellegrin, 1929; and Labeo sanagaensis Tshibwabwa, 1997. Such low diversity of Labeo species in the region is likely an underestimation reflecting taxonomic confusion caused by marked morphological similarity, resulting from convergent evolutionary processes that appear particularly widespread in this taxon (Liyandja, 2018; Liyandja et al., 2022).

Species delimitation of Labeo in LG remains problematic despite a morphology‐based revision of Tshibwabwa (1997) and the low number of currently described species. A new revision of these species, employing an integrative molecular and morphological approach, is therefore necessary to address the many outstanding taxonomic issues of Labeo species in the region.

In this paper, we provide a formal description for a population of Labeo from the Kouilou‐Niari River system (KNR), initially reported as potentially new to science by Liyandja et al. (2022). This particularly problematic taxon has variously been identified as L. cf. camerunensis (Liyandja et al., 2022), both L. annectens and L. lukulae (Mamonekene & Stiassny, 2012), L. camerunenis (Walsh et al., 2022) and Labeo sp. 2 (Liyandja et al., in review). Here, informed by a recent phylogenomic analysis (Liyandja et al., in review), we integrate traditional morphometrics, meristic and osteology (from micro‐CT scan images) to provide a formal taxonomic description resolving this long‐standing case of repeated misidentification and taxonomic confusion. We focus on selected features of potential diagnostic utility for future studies aimed at morphology‐based species descriptions of the numerous cryptic/candidate Labeo species revealed by ongoing phylogenomic studies.

2. MATERIALS AND METHODS

2.1. Ethics statement

The present description was based on specimens collected from the KNR basin (Figure 1) by Gina Walsh and Victor Mamonekene (Mamonekene & Stiassny, 2012; Walsh et al., 2014) between 2010 and 2013. All collections were conducted in accordance with the guidelines for the use of fishes in research (AFS/AIFRB/ASIH, 2003). The collection and exportation of these fishes were conducted with permission of the Congolese Ministère du Développement Durable et de l'Economie Forestière, Direction de l'Economie Forestière (permit# 178465 and permit# 1125526, both on file at AMNH).

FIGURE 1.

FIGURE 1

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Map of the Kouilou‐Niari River system showing geographic locations of collection sites for the type series of Labeo niariensis sp. nov. Red star = holotype; yellow star = paratypes.

2.2. Morphometric and meristic data collection and analyses

Institutional abbreviations follow Sabaj (2020). Throughout the text, modal values for meristic counts are underlined. SL and HL refer to standard length and head length, respectively. In total, we included 49 specimens from the LG ichthyofaunal province in the analysis. Twenty‐two morphometric measurements and 19 meristic counts (Tables 1 and 2) were made following Tshibwabwa and Teugels (1995) and slightly modified following Tshibwabwa et al. (2006), Moritz (2007), Moritz and Neumann (2017) and Armbruster (2012). We measured both the least depth (at the narrowest point of the caudal peduncle) and the greatest depth (measured vertically from the posterior insertion of the anal fin) of the caudal peduncle. Measurements were made point‐to‐point, except for the caudal peduncle and postorbital length, which were measured as the horizontal distances, using digital callipers. Body depth (BD) was measured as a vertical distance from the posterior insertion of the dorsal fin to the ventrum. X‐ray images were used to count total (abdominal plus caudal) vertebrae, number of pleural ribs, simple dorsal‐ and anal‐fin rays, caudal‐fin principal and procurrent rays. Contrary to Tshibwabwa et al. (2006) and Tshibwabwa and Teugels (1995), all vertebrae possessing a haemal arch were counted as caudal vertebrae (Aguirre et al., 2014), and Weberian vertebrae and the pleural centrum were excluded from all vertebral counts. Circumpeduncular scales were counted at the narrowest point of the caudal peduncle (Reid, 1985). Morphometric and meristic data were separately analysed using R (R Core Team, 2013). Meristic data are size independent and were analysed using principal component analysis (PCA) as implemented in the package FactoMineR (Lê et al., 2008). Invariant meristic counts (principal caudal‐fin rays, simple pelvic‐fin rays, branched pelvic‐fin rays, simple anal‐fin rays and branched anal‐fin rays) were removed from the analyses. Morphometric data, which are size dependent, were analysed following the multivariate ratio method proposed by Baur and Leuenberger (2011). We used the morphometric PCA and PCA ratio spectrum to identify potentially diagnostic ratios. For the morphometric PCA, raw measurements were standardized by dividing each variable by its geometric population mean. Fin ray measurements were excluded from morphometric analyses due to damaged fins, and two topotypes of L. annectens (BMNH 1902.11.12:138 and BMNH 1904.2.29:31), with bodies strongly deformed by preservation, were also excluded from these analyses.

TABLE 1.

Morphometrics of the holotype and eight paratypes of Labeo niariensis sp. nov.

Morphometric measurements Holotype Holotype + paratypes
Maximum Minimum Mean ± SD
Standard length (SL) (mm) 118.3 128.9 67.8 108.6 ± 18.4
Head length (HL) (mm) 28.9 32.7 17.29 27.1 ± 4.5
Body depth (BD) (mm) 22.5 25.2 12.1 21.2 ± 4
Caudal peduncle length (CPL) (mm) 17.4 18.86 9.72 15.5 ± 2.6
%SL
BD 19 20.6 17.9 19.5 ± 0.9
Caudal peduncle depth (CPD) 12.8 13.3 12.6 12.9 ± 0.3
HL 24.4 26.2 23.8 25.0 ± 0.7
Pre‐dorsal length (PDL) 46.8 51.4 46.8 48.4 ± 1.3
Pre‐anal length (PAL) 79.2 81.8 78 80.0 ± 1.3
Pre‐ventral length (PVL) 55.7 58.7 55.7 57.0 ± 1.1
Pre‐pectoral length (PPL) 24.6 26 23.6 25.1 ± 0.8
Dorsal‐fin base length (DFL) 18.1 19.7 17.1 18.3 ± 0.9
Dorsal‐fin length (DRL) 25.5 26.8 22.6 24.8 ± 1.4
Pectoral‐fin length (PL) 22.4 23.3 19.8 21.7 ± 1.1
Ventral‐fin length (VL) 18.8 19.1 16.9 18.1 ± 0.7
Anal‐fin base length (AL) 7.7 8.9 6.9 7.7 ± 0.6
Anal‐fin length (ARL) 19.5 20.3 18.4 19.2 ± 0.6
Vent–anal‐fin length (GO) 4.1 4.6 3.4 4.2 ± 0.4
CPL 14.7 14.7 13.4 14.3 ± 0.5
%HL
Snout length (SnL) 53.4 59.7 49.2 53.6 ± 3.1
Interorbital width (IOD) 45.2 45.5 40.2 43.1 ± 1.8
Internarial width (IND) 33.5 33.7 28.9 31.4 ± 1.7
Bony eye orbital diameter (ED) 27.6 29 24.3 26.5 ± 1.5
Postorbital length (POL) 26.1 27 15.6 24.0 ± 3.5
Gape width (GD) 38.1 47.5 35.8 41.4 ± 4.2
%BD
Interpectoral width (IPW) 80.6 89 73.3 81.1 ± 4.3
Interventral width (IPVW) 53.6 61.4 50.2 53.8 ± 3.6
%CPL
CPD 115.1 116.4 105.7 110.5 ± 3.6
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TABLE 2.

Meristics of the holotype and eight paratypes of Labeo niariensis sp. nov.

Meristic counts Holotype Holotype + paratypes
Maximum Minimum Mode
Simple dorsal‐fin rays 4 4 4 4
Branched dorsal‐fin rays 9 9 9 9
Scales in lateral line 34 + 3 34 + 3 34 + 3 34 + 3
Scale rows between lateral line and dorsal fin 4 5 4 4
Scale rows between lateral line and ventral fin 3 3 3 3
Scales around caudal peduncle 12 12 12 12
Pre‐dorsal scales 12 12 11 11
Principal caudal‐fin rays 19 19 19 19
Upper procurrent caudal‐fin rays 10 10 9 10
Lower procurrent caudal‐fin rays 9 9 8 8
Simple ventral‐fin rays 1 1 1 1
Branched ventral‐fin rays 8 8 8 8
Simple anal‐fin rays 3 3 3 3
Branched anal‐fin rays 5 5 5 5
Total vertebrae 31 31 30 31
Abdominal vertebrae 17 17 17 17
Caudal vertebrae 14 14 13 14
Pre‐dorsal vertebrae 6 6 6 6
Pleural ribs 13 13 12 13
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2.3. CT scan image collection

Three representatives of the new species were CT‐scanned at the AMNH Microscopy and Imaging Facility (MIF) using both the nanofocus (180 kV/20 W) and the microfocus (240 kV/320 W) tubes of a Phoenix V|tome|XS240 micro‐CT scanner (General Electric, Fairfield, CT, USA) depending on specimen size. Additionally, one or two representatives of each described Labeo species from LG, except for L. camerunensis for which materials were not available, were CT‐scanned. Specimens were scanned at resolutions varying between 18.1 and 64.02 μm, depending on their size, with a beam energy varying between 110 and 160 kV and 90–180 μA using a diamond target. A total of 2000 to 2500 projections per specimen were collected for 400 ms each and averaged three to four times to improve the signal‐to‐noise ratio. Image reconstructions were performed using the Phoenix datosjx (General Electric, Wunstorf, Germany) reconstruction software and imported into Volume Graphics Studio Max 2024 (Volume Graphics, Heidelberg, Germany) for segmentation and visualization, and edited using Adobe Photoshop 2024.

3. RESULTS

3.1. Meristics

After removing invariant meristic counts, a PCA was performed on the remaining 14 meristic counts. In this analysis, 78.9% of meristic variation was explained by the first four principal components, with PC1 and PC2 accounting for 44.8% and 17% of variation in the data, respectively. Eight of the 14 variables helped explain variation in the first two principal component axes. Differences in vertebral counts contributed most to the factor loadings of PC1, with the number of pre‐dorsal vertebrae (14.2%) and total vertebrae (12.3%) having the greatest influence, whereas differences in abdominal vertebrae (15.9%), circumpeduncular scales (14.8%), pleural ribs (12.5%) and lateral‐line scales (10.5%) contributed most to loadings of PC2. Plotting PC1 against PC2 (Figure 2) separates these species into three groups: L. lukulae with lower pre‐dorsal (4 vs. 5–6), abdominal (14–15 vs. 16–19) and total (28–29 vs. 30–33) vertebral counts; L batesii and L. nunensis with higher abdominal vertebral counts (18–19 vs. 14–17); and L. annectens, L. camerunensis, L. niariensis sp. nov. and L. sanagaensis with intermediate abdominal vertebral counts (16 or 17) and medium‐to‐higher pre‐dorsal vertebral counts (5 or 6). Also, in this biplot, L. niariensis sp. nov. is clearly distinguished from all the remaining LG species, yet it is positioned close to topotypical specimens of L. annectens in morphospace (Figure 2).

FIGURE 2.

FIGURE 2

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Principal component analysis (PCA) biplot of PC1 against PC2 for an analysis of 14 meristic counts for 49 specimens of sampled Lower Guinean Labeo taxa.

3.2. Morphometrics

Morphometric PCA was performed on 19 measurements (excluding fin ray measurements) of 47 specimens. The first four principal components accounted for 82.1% of total variation in the data, with PC1 and PC2 accounting for 49.5% and 18% of the variation, respectively. Differences in vent–anal‐fin distance, greatest caudal peduncle depth (CPD), internarial width, least CPD, interorbital width and postorbital length contributed the most to PC1, whereas differences in orbit length, least and greatest CPD, caudal peduncle length, head length, pre‐pectoral length and dorsal‐fin base length contributed the most to PC2 (see Table S1 in Supporting Information). The biplot of PC1 against PC2 clearly separates L. camerunensis, L. niariensis sp. nov. and L. lukulae from all other species (L. annectens, L. batesii, L. nunensis and L. sanagaensis; Figure 3). Examination of the PCA ratio spectrum suggests that most variation in PC1 is explained by three ratios: vent–anal‐fin distance/greatest CPD, vent–anal‐fin distance/internarial width and vent–anal fin distance/least CPD. On the contrary, most variation in PC2 is explained by three other ratios: orbit length/least CPD, orbit length/greatest CPD and caudal peduncle length/least CPD (see Figures S1 and S2 in Supporting Information). A plot of vent–anal‐fin distance/greatest CPD and orbit length/least CPD ratios (Figure 4a,b) against the natural log of standard length highlights the difference between L. niariensis sp. nov. and the remaining species (see Figures S3 and S4 in Supporting Information for additional comparisons).

FIGURE 3.

FIGURE 3

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Principal component analysis (PCA) biplot of PC1 against PC2 for an analysis of 19 morphometric measurements for 47 specimens of sampled Lower Guinean Labeo taxa.

FIGURE 4.

FIGURE 4

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Major axis regressions of (a) vent–anal‐fin distance to greatest caudal peduncle depth and (b) orbital bony length to least caudal peduncle length ratios, plotted against the natural log of standard length.

3.3. Taxonomic account

L. niariensis, sp. nov.

Figures 5 and 6; Tables 1 and 2.

FIGURE 5.

FIGURE 5

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Photographs of the holotype of Labeo niariensis sp. nov. (AMNH 264174, 118.3 mm SL): (a) postmortem and (b–d) ethanol preserved, shown in lateral, dorsal and ventral views, respectively.

FIGURE 6.

FIGURE 6

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Osteological comparison of Lower Guinean Labeo: (a) Labeo niariensis (holotype AMNH 264174): posterior neurocranium and anterior axial elements, isolated kinethmoid, left infraorbital series, urohyal, left fifth ceratobranchial; (b) Labeo annectens (topotype ANSP 92427): posterior neurocranium and anterior axial elements, isolated kinethmoid, left infraorbital series; (c) Labeo lukulae (topotype AMNH 276343, tag LKL25): posterior neurocranium and anterior axial elements, isolated kinethmoid, left infraorbital series; (d) Labeo nunensis (AMNH 249816): isolated kinethmoid, left infraorbital series. Not to scale.

Labeo sp. 2 (Liyandja et al., in review).

L. cf. camerunensis (Liyandja et al., 2022).

L. annectens, L. lukulae (Mamonekene & Stiassny, 2012).

L. camerunenis (Walsh et al., 2022).

ZooBank accession numbers: urn:lsid:zoobank.org:act:EC9EC9E3‐F3EF‐4871‐ADEF‐EAB1A99A3BCE and urn:lsid:zoobank.org:pub:48CE05B6‐0512‐4E3A‐B7F9‐C38CF90E44AE.

3.3.1. Holotype

AMNH 264174 [tissue AMCC 235701, GenBank accession: ON751960 (COX1) and ON778509 (RAG1)], 118.3 mm SL, main channel of the Léala River, a subtributary of the Niari River (Kouilou‐Niari basin), at the bridge with the road P1, about 1.62 km in a straight line upstream of its confluence with the Louessé River, Niari Department, Republic of Congo, −2.224389°, 12.819389°, G. Walsh et al., October 2013.

3.3.2. Paratypes

AMNH 264150, one individual, 128.9 mm SL, main channel of the Louessé River, a tributary of the Niari River (Kouilou‐Niari basin), at Mayoko village, about 72 km in a straight line north of Massendjo, Niari Department, Republic of Congo, −2.290861°, 12.792333°, G. Walsh et al., October 2013; AMNH 256425 (tissue AMCC 221811), one, 97.0 mm SL, same locality as holotype, V. Mamonekene, April 2012; AMNH 256506, one, 121.9 mm SL, same locality as holotype, V. Mamonekene, April 2012; AMNH 256526, two, 67.8–109.1 mm SL, same locality as AMNH 264150, V. Mamonekene, April 2012; AMNH 253942, one, 113.46 mm SL, main channel of the Niari River at Loudima, Niari Department, Republic of Congo, −4.100278°, 13.060556°, V. Mamonekene, December 2010. ROM 116816, one, 100.61 mm SL, same locality as holotype, V. Mamonekene, April 2012. SAIAB 246351, one, 120.19 mm SL, same locality as holotype, V. Mamonekene, April 2012.

3.3.3. Diagnosis

L. niariensis is unique among congeners in the possession of a deeply bifurcate posterior process of the kinethmoid bone (Figure 6a). Additionally, it is readily differentiated from all LG congeners, except L. annectens and L. nunensis, by possessing six (vs. five or fewer) pre‐dorsal vertebrae (Figure 6). It is further distinguished from L. annectens and L. nunensis by the presence of a prominent anterior notch and only moderately developed posterior process on the first infraorbital (lachrymal) versus absence of an anterior notch and an elongated posterior process, and the presence of a deeply ovoid second infraorbital versus narrow and elongated (Figure 6).

L. niariensis differs from L. annectens by a lower (30 or 31 vs. 31 or 32) total vertebral count with 13 or 14 (vs. 15 or 16) caudal vertebrae, and 34 (vs. 35) pored lateral‐line scales (to the end of the hypural plate), by a longer head (23.8%–26.2% vs. 19.6%–22.6% SL), shorter (3.4%–4.6% vs. 4.7%–7.7% SL) vent–anal‐fin distance, lower (25.9%–35.4% vs. 36.2%–59.3%) vent–anal‐fin distance to greatest CPD ratio and higher (45.8%–56.8% vs. 31.3%–45.7%) orbital length to least CPD ratio. L. niariensis can be distinguished from L. batesii, L. lukulae, L. nunensis and L. sanagaensis by having 9 (vs. 10 or 11) branched dorsal‐fin rays, and from L. camerunensis (and L. batesii) by having 12 (vs. 16) circumpeduncular scales. Further, the new species is distinguished from L. batesii and L. nunensis by a shallower body (BD 17.9%–20.6% vs. 20.9%–27.5% SL) and caudal peduncle (CPD 12.6%–13.3% vs. 15.2%–18.3% SL); from L. batesii, L. nunensis and L. sanagaensis by a shorter (17.1–19.7 vs. 19.8–23.7% SL) dorsal‐fin base and longer caudal peduncle (CPL 105.7%–116.4% vs. < 93% CPD); from L. camerunensis, L. lukulae and L. sanagaensis by a shorter (3.4%–4.6% vs. 5.1%–8.5% SL) vent–anal‐fin distance; from L. lukulae by higher (30–31 vs. 28–29) vertebrae counts, a longer (55.7%–58.7% vs. 49.9%–55.6% SL) pre‐pelvic distance and lower (22.8%–32.7% vs. 51.9%–66.9%) vent–anal‐fin distance to greatest CPD ratio; from L. camerunensis by a smaller (35.8%–47.5% vs. 49.8%–54.2% HL) mouth gape; and from L. nunensis by lower (30–31 vs. 32–33) total vertebrae counts with 17 (vs. 18 or 19) abdominal vertebrae.

3.3.4. Description

Based on the holotype and eight paratypes. General appearance as in Figure 5; proportional measurements and meristic counts are presented in Tables 1 and 2, respectively. Small‐bodied species, maximum observed size 128.9 mm SL (AMNH 264150), with elongated cylindrical body form. Genital opening well in advance of anal‐fin origin, vent–anal‐fin distance 3.4%–4.6% SL. Head moderately large, length 23.8%–26.2% SL, interorbital space slightly convex. Snout prominent, length 49.2%–59.7% HL, more‐or‐less rounded, often with shallow ethmoid furrow, poorly developed fleshy appendage with numerous minute tubercles. Eyes large, orbital diameter 24.3%–29% HL, dorsolateral not visible in ventral view. Mouth inferior, relatively large with plicate lips; anterior barbels absent, posterior barbels small, deeply embedded in lip fold, rarely visible.

Dorsal fin concave, inserted at mid body, four simple and nine branched rays. Anal fin, with three simple and five branched rays. Caudal fin deeply forked, 9 or 10 upper procurrent, 8 or 9 lower procurrent and 19 (2 unbranched and 17 branched) principal rays. Pectoral fin lateroventral, longest ray 19.8%–23.3% SL. Ventral fin slightly shorter than pectoral fin, longest ray 16.9%–19.1% SL, one procurrent, one simple, eight branched rays. Anal fin relatively short (base 6.9%–8.9% SL), not reaching caudal‐fin base, longest ray 18.4–20.3% SL.

Scales cycloid, 34 pored scales in lateral line; 4 or 5 rows between lateral line and dorsal‐fin origin; 3 rows between lateral line and ventral‐fin origin, 12 circumpeduncular scale rows.

3.3.5. Osteology

Presence of a deeply bifurcate (bi‐lobed) posterior process of the kinethmoid bone (Figure 6a), absent in congeners (e.g., Figure 6b,c) and interpreted here as a diagnostic for the species. Infraorbital series includes a broad first infraorbital (lachrymal) with a prominent deep, anterior notch but only a moderately developed posterior process (compare Figure 6a with b,c), second infraorbital deeply ovoid and followed by three additional elements. Pharyngeal bones (fifth ceratobranchial) triangular in overall shape and bear long‐necked teeth with ovoid, bevelled cusps inserted in three rows, from outer to inner, with two, four and five teeth, respectively (Figure 6a). Urohyal robust, lacking a collum, slightly longer than deep with a somewhat fenestrated lamellar body (Figure 6a). Axial skeleton, exclusive of modified Weberian vertebrae, comprises 30–31 vertebrae with 17 abdominal (6 of which are pre‐dorsal) and 13–14 caudal vertebrae (exclusive of terminal pleural centrum). Number of pre‐dorsal vertebrae (6) is constant, but unusually for Labeo species, the number of supraneurals varies from four to six among specimens examined.

3.3.6. Colouration

Immediately postmortem (Figure 5a) colouration varies from dark brown to dark grey above and light grey to whitish below. Prominent patterns of black pigmentation encircling flank scales present in postmortem specimens, barely visible in preservation. Preserved specimens (Figure 5b), dark brown above and brown to beige below, with faint lateral stripe and ovoid black spot on caudal peduncle extending to scaly caudal‐fin base.

3.3.7. Distribution

Known only from the KNR system, Niari Department, Republic of Congo. Figure 1 shows the distribution of L. niariensis in the KNR system.

3.3.8. Biology and ecology

All specimens of L. niariensis have been collected in the upper and middle Niari River basin. According to Walsh et al. (2022), the upper basin of the KNR, where most L. niariensis were collected, is characterized by high gradient habitats. Mamonekene and Stiassny (2012) reported that at Loudima, where additional L. niariensis specimens were collected, the Niari flows with a strong current. These observations, combined with dorso‐ventral body compression and an inferior mouth placement, suggest that L. niariensis is likely associated with fast‐flowing benthic habitats. Nevertheless, little is known about the ecology and habitat requirements of this species, and further ecological studies are needed.

3.3.9. Etymology

L. niariensis refers to the Department of Niari in the Republic of Congo (Central Africa), where the entire type series was collected. Species name to be treated as an adjective derived from the toponym Niari (Department of Niari).

3.3.10. Comparative material

A total of 46 specimens from the LG ichthyofaunal province were included in our analyses. Apart from the 9 specimens of the new species, 37 other specimens comprise the following:

7 L. annectens [lectotype: BMNH 1902.11.12.137; paralectotype: BMNH 1902.11.12.138: one individual; topotype: ANSP 92427, one (CT‐scanned), BMNH 1906.5.28.57: one, BMNH 1904.2.29.29–31: two of three examined]; 3 L. batesii [holotype: BMNH 1912.6.23.3; AMNH249817: one (CT‐scanned); AMNH 249818: one]; 3 L. camerunensis (holotype: BMNH 1973.5.14.324; paratypes: BMNH 1973.5.14.322–323: two); 16 L. lukulae [topotype: AMNH 276342: seven, AMNH 276343: six; ANSP 38553: one, AMNH 274961: one (CT‐scanned), AMNH 274962: one]; 3 L. nunensis Pellegrin, 1929 [syntype: MNHN‐1928‐0303: one; AMNH 249816: one (CT‐scanned), AMNH 251713: one individual]; and 6 L. sanagaensis [AMNH 249854: two, AMNH 249853: one (CT‐scanned), CU 93456: four].

4. DISCUSSION

Despite Tshibwabwa's (1997) revision of the LG Labeo, identification and delimitation of the species within the region remain extremely challenging. A study conducted on Labeo of the Congo Basin (Van Steenberge et al., 2016) suggested that many of the features used in traditional species delimitation (Tshibwabwa, 1997; Tshibwabwa & Teugels, 1995), such as the shape and size of the dorsal fin, exhibit considerable allometric and geographic variation. Recent studies (Liyandja, 2018; Liyandja et al., 2022) concluded that in addition to these character problems, convergent evolution in body shape has resulted in similar ecomorphs in distantly related species, making it extremely difficult to distinguish species using traditional techniques alone. Compounding these problems is a combination of confusion about type localities and typological species concepts that has exacerbated systematic problems within the group (Liyandja & Stiassny, 2023). An outstanding example of type locality confusion in the region is the case of L. annectens Boulenger (1903).

Boulenger (1903) reported the type locality of L. annectens as near Efulen (Efoulan) in southern Cameroon, and that the type specimens were collected in a small tributary of the Campo River (Ntem River). However, in a subsequent publication, Boulenger (1909) reported that the type series were from the Kribi River (Kienke River) at Efulen and expanded the species range to include both the Ogooué (Ogowe) and the Congo (Dja River) river systems. Based on Boulenger (1909), Reid (1985) reported the Campo River as a tributary of the Kribi River but did not recognize L. annectens as a valid species. Later, Tshibwabwa (1997), based on Boulenger's original description of L. annectens, reported the Campo River as type locality for this species. When revalidating the species status of L. annectens, Tshibwabwa (1997) expanded its distribution to the Sanaga, Kouiloui‐Niari and the rest of the Congo River system. However, Tshibwabwa's redescription of L. annectens included several specimens of distantly related species, including specimens of the new species described here. The inclusion of several species in Tshibwabwa's redescription of L. annectens, the main reference for the identification of Labeo species in LG, explains why the diagnostic features he provided for L. annectens are shared by several different species. Even in the recently published study of Liyandja et al. (2022), specimens identified as L. annectens (from the Ogooué River) were in fact misidentified, as the authors were unable to access the type specimens or topotypic tissue samples. This long‐standing situation of problematic identification keys and lack of diagnostic features has hindered the discovery and description of numerous Labeo species. Recently, however, deep phylogenomic coverage, coupled with osteological (based on CT imagery) and morphometric analyses, has made possible the identification of several previously unrecognized lineages within the L. annectens complex of LG (Liyandja et al., in review), and this description is the first of a series of taxonomic works aimed at improving understanding of taxonomic diversity in the LG ichthyofaunal province.

About 17 major river systems, with differing levels of biogeographic isolation, are known in LG (Stiassny et al., 2007). Each with extensive habitat heterogeneity, including numerous rapids, steep‐sloped forested riverbanks, flooded savannahs and plains, swamp forests and different‐sized tributaries (Aimé et al., 1960; Mamonekene & Stiassny, 2012; Walsh et al., 2022), promotes speciation by habitat isolation. It is likely that each of these river systems has different endemic Labeo species, and the discovery of L. niariensis, after several years of exploration of the KNR system, emphasizes the importance of further integrative taxonomic studies in this and other LG river systems to improve our understanding of the true diversity of the region.

This description of L. niariensis is part of our ongoing efforts to resolve taxonomic problems within the African Labeo radiation. The description brings the total number of recognized Labeo species to over 110 of which over 70 live in Afrotropical freshwater systems. However, phylogenomic studies (Liyandja et al., in review) suggest that numerous other species and species complexes of Labeo across the continent need taxonomic revision, and many undescribed species are yet to be morphologically diagnosed.

AUTHOR CONTRIBUTIONS

Tobit L. D. Liyandja and Melanie L. J. Stiassny conceived and designed the study. Tobit L. D. Liyandja collected and analysed the data. Tobit L. D. Liyandja wrote the paper with input from Melanie L. J. Stiassny.

FUNDING INFORMATION

This research was funded by a grant from the Axelrod Research Curatorship (Melanie L.J. Stiassny), the Richard Gilder Graduate School, and the University of Toronto provost’s postdoctoral fellowship program.

CONFLICT OF INTEREST STATEMENT

We declare that this study was conducted in the absence of any commercial or financial relationships that could be considered as a potential conflict of interest.

Supporting information

Data S1.

JFB-107-592-s001.docx (219KB, docx)

Table S1.

JFB-107-592-s002.xlsx (11.5KB, xlsx)

ACKNOWLEDGEMENTS

The authors would like to thank the Natural History Museum (London) for providing X‐ray images and photographs of type series of L. annectens, L. batesii and L. camerunensis, and the National Museum of Natural History (Paris) for providing X‐ray and photographs of the holotype of L. nunensis. We are especially grateful to Gina Walsh for providing postmortem pictures of the holotype of the new species, Chrissy Williams NHM (London) for facilitating image transfers, Thomas Vigliotta, Radford Arrindell, Chloe Lewis, Ryan Thoni and Morgan Chase of the AMNH for technical assistance to Tobit L. D. Liyandja. We also gratefully acknowledge Don Stacey and Mary Burridge from the Royal Ontario Museum (ROM) for loan processing and technical assistance provided to Tobit L. D. Liyandja; Nathan Lujan for reviewing an earlier draft of this manuscript; and Nathan Lujan and Nathan Lovejoy for hosting Tobit L. D. Liyandja. We thank Casey Dillman, from the Cornell University Museum of Vertebrates, Brian Sidlauskas, from Fisheries, Wildlife and Conservation Sciences Department at the Oregon State University, and Mark H. Sabaj, from the Academy of Natural Sciences of Drexel University, for specimen loans, tissues gifts and sharing pictures of additional type specimens.

Liyandja, T. L. D. , & Stiassny, M. L. J. (2025). Hidden in plain view: A new Labeo (Cyprinidae: Labeoninae) endemic to the Kouilou‐Niari River basin in the Lower Guinea ichthyological province. Journal of Fish Biology, 107(2), 592–602. 10.1111/jfb.70062

REFERENCES

  1. Aguirre, W. E. , Walker, K. , & Gideon, S. (2014). Tinkering with the axial skeleton: Vertebral number variation in ecologically divergent three‐ spine stickleback populations. Biological Journal of the Linnean Society, 113, 204–219. [Google Scholar]
  2. Aimé, J. , Roche, M. , & Rodier, J. (1960). Monographie hydrologique du Kouilou Niari (Vol. 358). ORSTOM. [Google Scholar]
  3. Armbruster, J. W. (2012). Standardized measurements, landmarks, and meristic counts for Cypriniform fishes. Zootaxa, 3586, 8–16. [Google Scholar]
  4. Baur, H. , & Leuenberger, C. (2011). Analysis of ratios in multivariate morphometry. Systematic Biology, 60, 813–825. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Boulenger, G. A. (1902). Contributions to the ichthyology of The Congo. On some new fishes from the French Congo. Proceedings of the Zoological Society of London, 1, 234–237. [Google Scholar]
  6. Boulenger, G. A. (1903). On the fishes collected by Mr. G. L. bates in southern Cameroon. Proceedings of the Zoological Society of London, 1, 21–29. [Google Scholar]
  7. Boulenger, G. A. (1909). Catalogue of the fresh‐water fishes of Africa in the British museum (natural history) (Vol. 1, pp. 1–377). Taylor & Francis. [Google Scholar]
  8. Boulenger, G. A. (1911). Descriptions of three new freshwater fishes discovered by Mr. G. L. bates in South Cameroon. Annals and Magazine of Natural History (Series 8), 8, 372–373. [Google Scholar]
  9. Fricke, R. , Eschmeyer, W. N. , & Van der Laan, R. (2024). Eschmeyer's catalog of fishes: Genera, species, references . California Academy pf sciences. Available at http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp
  10. Froese, R. , & Pauly, D. (2024). FishBase. http://www.fishbase.org
  11. Lavoué, S. (2019). Origins of Afrotropical freshwater fishes. Zoological Journal of the Linnean Society, 20, 1–67 zlz039. 10.1093/zoolinnean/zlz039 [DOI] [Google Scholar]
  12. Lê, S. , Josse, J. , & Husson, F. (2008). FactoMineR: An R package for multivariate analysis. Journal of Statistical Software, 25, 1–18. [Google Scholar]
  13. Liyandja, T. D. L. (2018). Body shape evolution of African/Asian minnows of the genus Labeo cuvier 1817 (Cyprinidae, Labeonini) and variations in Labeo parvus. Master's thesis, Biological Sciences, Auburn University, Auburn, AL, 94 pp. https://etd.auburn.edu//handle/10415/6398
  14. Liyandja, T. L. D. , Armbruster, J. W. , Poopola, M. O. , & Stiassny, M. L. J. (2022). Evolutionary convergence in body shape obscures taxonomic diversity in species of the African Labeo forskalii group: Case study of L. parvus Boulenger 1902 and L. ogunensis Boulenger 1910. Journal of Fish Biology, 101, 898–913. [DOI] [PubMed] [Google Scholar]
  15. Liyandja, T. L. D. , Smith, B. T. , Alter, S. E. , Sidlauskas, B. L. , & Stiassny, M. L. J. (2025). Phylogenomics of African Labeo (Cypriniformes: Cyprinidae) emphasizing central African species. Molecular Phylogenetics and Evolution. in review 10.2139/ssrn.5147387. [DOI] [PubMed] [Google Scholar]
  16. Liyandja, T. L. D. , & Stiassny, M. L. J. (2023). Description of two new Labeo (Labeoninae; Cyprinidae) endemic to the Lulua River in the Democratic Republic of Congo (Kasai ecoregion); a hotspot of fish diversity in The Congo basin. Novitates, 2023(3999), 1–24. [Google Scholar]
  17. Lowenstein, J. H. , Osmundson, T. W. , Becker, S. , Hanner, R. , & Stiassny, M. L. J. (2011). Incorporating DNA barcodes into a multi‐year inventory of the fishes of the hyperdiverse lower Congo river, with a multi‐gene performance assessment of the genus Labeo as a case study. Mitochondrial DNA, 22, 52–70. [DOI] [PubMed] [Google Scholar]
  18. Mamonekene, V. , Ibala, A. Z. , & Stiassny, M. L. J. (2018). A new small bard (Cyprininae: Smiliogastrini) from the Louesse, Lekoumou (upper Niari basin), and Djoulou (upper Ogowe basin) rivers in the republic of Congo, west‐central Africa. Novitates, 2018(3917), 1–16. [Google Scholar]
  19. Mamonekene, V. , & Stiassny, M. L. J. (2012). Fishes of the Du Chaillu Massif, Niari depression, and Mayombe massif (republic of Congo, west‐central Africa): A list of species collected in tributaries of the upper Ogowe and middle and upper Kouilou‐Niari River basins. Check List, 8, 1172–1183. [Google Scholar]
  20. Mipounga, H. K. , Cutler, J. , Mve Beh, J. H. , Adam, B. , & Sidlauskas, B. L. (2019). Enteromius pinnimaculatus sp. nov. (Cypriniformes: Cyprinidae) from southern Gabon. Journal of Fish Biology, 96, 1218–1233. [DOI] [PubMed] [Google Scholar]
  21. Moritz, T. (2007). Description of a new cyprinid species, Labeo meroensis n. sp. (Teleostei: Cyprinidae), from the river Nile. Zootaxa, 1612(1), 55–62. 10.11646/zootaxa.1612.1.4 [DOI] [Google Scholar]
  22. Moritz, T. , & Neumann, D. (2017). Description of Labeo latebra (Cyprinidae) from the Nile river in Sudan. Cybium, 41, 25–33. [Google Scholar]
  23. Pellegrin, J. (1929). Description d'une variété nouvelle du Labeo chariensis Pellegrin, recueillie au Cameroun par M. Th. Monod. Bulletin de la Société Zoologique de France, 54, 288–290. [Google Scholar]
  24. R Core Team . (2013). R: A language and environment for statistical computing. R foundation for statistical computing. Retrieved from http://www.r-project.org/ [Google Scholar]
  25. Reid, G. M. (1985). A revision of the African species of Labeo (Pisces: Cyprinidae) and a re‐definition of the genus. Verlag van J. Crammer. [Google Scholar]
  26. Sabaj, M. H. (2020). Codes for natural history collections in ichthyology and herpetology. Copeia, 108(3), 593–669. 10.1643/asihcodons2020 [DOI] [Google Scholar]
  27. Snoeks, J. , Harrison, I. J. , & Stiassny, M. L. J. (2011). The status and distribution of freshwater fishes. In Darwall W., Smith K., Allen D., Holland R., Harrison I., & Brooks E. (Eds.), The diversity of fife in Africa freshwaters: Under threat. An analysis of the status and distribution of freshwater species throughout mainland Africa (pp. 42–87). IUCN. [Google Scholar]
  28. Sonet, G. , Snoeks, J. , Nagy, Z. T. , Vreven, E. , Boden, G. , Breman, F. C. , Decru, E. , Hanssens, M. , Ibala Zamba, A. , Jordaens, K. , Mamonekene, V. , Musschoot, T. , Van Houdt, J. , Van Steenberge, M. , Wamuini, L. S. , & Verheyen, E. (2019). DNA barcoding fishes from The Congo and the lower Guinean provinces: Assembling a reference library for poorly inventoried fauna. Molecular Ecology Resources, 19, 723–743. [DOI] [PubMed] [Google Scholar]
  29. Stiassny, M. L. J. , Teugels, G. G. , & Hopkins, C. D. (2007). The fresh and brackish water fishes of lower Guinea, west‐Central Africa (Vol. I and II, p. 800). IRD Editions. [Google Scholar]
  30. Trewavas, E. (1974). The freshwater fishes of rivers Mungo and meme and lakes Kotto, Mboandong and Soden, west Cameroon. Bulletin of the British museum (natural history): Zoology, 26, 331–419. 10.5962/bhl.part.208 [DOI] [Google Scholar]
  31. Tshibwabwa, S. M. (1997). Systématique des espèces africaines du genre Labeo (Teleostei; Cyprinidé) dans les régions ichtyogéographiques de basse‐Guinée et du Congo. Presses Univ. de Namur. [Google Scholar]
  32. Tshibwabwa, S. M. , Stiassny, M. L. J. , & Schelly, R. C. (2006). Description of a new species of Labeo (Telostei: Cyprinidae) from the lower Congo river. Zootaxa, 1224, 33–44. [Google Scholar]
  33. Tshibwabwa, S. M. , & Teugels, G. G. (1995). Contribution to the systematic revision of the african cyprinid fish genus Labeo: Species from the lower Zaire river system. Journal of Natural History, 29(6), 1543–1579. 10.1080/00222939500770661 [DOI] [Google Scholar]
  34. Van Steenberge, M. , Gajdzik, L. , Chilala, A. , Snoeks, J. , & Vreven, E. (2016). Don't judge a fish by its fins: Species delineation of Congolese Labeo (Cyprinidae). Zoologica Scripta, 46(3), 264–274. 10.1111/zsc.12203 [DOI] [Google Scholar]
  35. Walsh, G. , Jonker, M. N. , & Mamonekene, V. (2014). A collection of fishes from tributaries of the lower Kouilou, Noumbi and smaller coastal basin systems, Republic of the Congo, lower Guinea, west‐central Africa. Check List, 10, 900–912. [Google Scholar]
  36. Walsh, G. , Pease, A. A. , Woodford, D. J. , Stiassny, M. L. J. , Gaugris, J. Y. , & South, J. (2022). Functional diversity of Afrotropical fish communities across river gradients in the republic of Congo, west central Africa. Frontiers in Environmental Science, 10, 981960. 10.3389/fenvs.2022.981960 [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Data S1.

JFB-107-592-s001.docx (219KB, docx)

Table S1.

JFB-107-592-s002.xlsx (11.5KB, xlsx)

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