Labeo sp.

Liyandja, Tobit L. D. & Stiassny, Melanie 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, American Museum Novitates 2023 (3999), pp. 1-24 : 9-12

Labeo sp. ‘mbimbii’: Liyandja et al., 2022

HOLOTYPE: 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.

PARATYPES: 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 Province , 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 downstream 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 .

ADDITIONAL NONTYPE MATERIAL: AMNH 269104 (11), 53.48–82.13 mm SL, same locality as holotype, J.J. Mbimbi and T. Liyandja, September 2014 .

DIFFERENTIAL DIAGNOSIS: While no unambiguous morphological autapomorphies have been located to diagnose Labeo mbimbii , the species is distinguished from all central African

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-fin base (DFL) 21.1 26.5 19.2 22.0±1.4

Dorsal-fin length (DRL) 24.9 26.9 22.6 24.8±1.2

Pectoral-fin length (PL) 22 23.5 20.0 22.3±0.9

Pelvic-fin length (VL) 20 21.4 18.1 19.8±0.8

Anal-fin base (AL) 8.6 8.6 7.1 7.8±0.3

Anal-fin length (ARL) 18.8 21.4 18.4 19.7±1.0

Vent–anal-fin 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-fin rays 3 3 3 3

Branched dorsal-fin rays 9 10 9 10

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-fin rays. It is further distinguished from L. manasseeae , n. sp., in the possession of a snout with a deep ethmoid furrow and well-developed fleshy appendage vs. a snout with a shallow ethmoid furrow and weakly developed fleshy appendage, and a robust, deep-keeled, thick-necked urohyal bone (vs. gracile, shallow keeled with narrow neck).

DESCRIPTION: Based on holotype and 25 paratypes. General appearance as in figure 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-fin origin, vent–anal-fin distance 4.1%–6.7% SL. Head moderately large, with slightly convex or flattened interorbital space. Snout broad and truncate, ethmoid furrow deep, well-developed fleshy appendage with few (five to eight, generally five) 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 fin, iii 9 or 10 rays, margin slightly concave, inserted a little in front of midbody (predorsal length 46.2%–50.2% SL), anal fin, iii 5 rays. Caudal fin emarginate, 8–9 upper, 7–8 lower procurrent rays, 19 principal rays. Pectoral fins broad, inserted lateroventrally, interpectoral width 100.2%–117.8% BD. Pelvic fins, 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-fin origin; 3–3.5 between lateral line and pelvic-fin 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 figure 6. The Weberian apparatus of L. mbimbii is relatively massive (fig. 6A), with the anterior Weberian 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 first predorsal centrum. Four supraneural bones anterior to the neural spines of predorsal centra 2–5. Five predorsal vertebrae. Urohyal (fig. 6B) robust, thick-necked, with a deep keel. Infraorbital series (fig. 6C) consists of an elongate first infraorbital (lachrymal) and four additional elements, none of which are ventrally expanded or in contact with the preopercle.

COLORATION: Immediately postmortem (fig. 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 (fig. 5B–D) are dark brown above and paler brown below. A dark lateral band is visible in preserved juveniles.

DISTRIBUTION: A Lulua River endemic, known from the main channel of the lower and middle Lulua basin (fig. 1).

BIOLOGY AND ECOLOGY: All specimens of L. mbimbii have been collected in rapids along the Lulua River main channel over rocky substrates. These observations, combined with a dorsoventrally compressed body shape, suggest that L. mbimbii is adapted to rapid, rocky main-channel habitats. The waters where specimens have been collected are slightly acidic (pH 5.5–6.5), with low conductivity (2–5 µS/cm 2) and low concentrations of dissolved solids (TDS 4–10 ppm).

ETYMOLOGY: 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 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, including those described in the present paper. We dedicate this species to his outstanding work and commitment to biodiscovery and conservation in the Kasai basin .