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 : 14-17

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

HOLOTYPE: 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 Province, D.R.C., 09°41′37.2″S, 022°51′30″E, J.J. Mbimbi and T. Liyandja, September 2014.

PARATYPES: 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 .

ADDITIONAL NONTYPE MATERIAL: 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 .

DIFFERENTIAL DIAGNOSIS: 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 manasseeae 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-fin 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 vertebrae (vs. 5), a pointed snout with a shallow ethmoid furrow and weakly developed fleshy appendage versus a truncate snout with a deep ethmoid furrow and well-developed fleshy appendage, and a gracile, narrow-necked, shallow-keeled (vs, robust, thick-necked, and deep-keeled) urohyal bone.

DESCRIPTION: Based on the holotype and five paratypes. General appearance as in figure 7, proportional measurements and meristic counts in table 2. Small-bodied species, maximum observed size 121.2 mm SL (holotype), elongate, cylindriform, somewhat dorsoventrally compressed ( BD 16.1 %–19.2% SL). Genital opening situated well in advance of anal-fin origin, vent –

five 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-fin base (DFL) 20.0 22.7 19.6 20.8±1.2

Dorsal-fin length (DRL) 24.2 27.9 23.7 26.2±1.8

Pectoral-fin length (PL) 20.5 21.8 18.9 20.7±1.0

Pelvic-fin length (VL) 17.9 19.1 16.9 18.3±0.8

Anal-fin base (AL) 7.5 8.5 7.3 7.7±0.4

Anal-fin length (ARL) 18.8 19.2 16.9 18.5±0.8

Vent–anal-fin 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-fin rays 4 4 4 4

Branched dorsal-fin rays 10 10 10 10

anal-fin distance 5.0%–6.9% SL. Head moderately large, with slightly convex interorbital space. Snout narrow and pointed, ethmoid furrow shallow, weakly developed fleshy 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 fin, iv10 rays, margin slightly concave, inserted just anterior to midbody (predorsal length 44.8%–48.0% SL), anal fin iii5 rays. Caudal fin strongly emarginate, 8 upper, 6–7 lower procurrent rays, 19 principal rays. Pectoral fins broad, inserted lateroventrally, interpectoral width 94.7%–107.9% BD. Pelvic fins, i8, slightly shorter than pectorals.

Scales cycloid, 30–31 in lateral line to hypural joint; 4 between lateral line and dorsal-fin origin; 3 between lateral line and pelvic-fin 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.

The Weberian apparatus of L. manasseeae is relatively massive (fig. 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 first predorsal centrum. Three 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 in all other specimens). Four predorsal vertebrae. Urohyal (fig. 8B) is gracile, thin necked, with a shallow keel. Infraorbital series (fig. 8C) consists of an elongated first infraorbital (lachrymal) and four additional elements, none of which are ventrally expanded or in contact with the preopercle.

COLORATION: Immediately postmortem (fig. 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 (fig. 7B–D) are dark brown above and brown below, and dark lateral band is visible in most specimens.

DISTRIBUTION: A Lulua River endemic, Labeo manasseeae is known mainly from the middle basin, with single records from the lower and upper basins (fig. 1). However, due to inaccessibility the upper Lulua has been poorly sampled ( Mbimbi et al., 2021) and it is likely that additional collecting efforts will expand the range of this species.

BIOLOGY AND ECOLOGY: 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. The 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/cm 2), and low concentration of dissolved solids (TDS 4–10 ppm).

ETYMOLOGY: Dedicated to Manassée W.E. Liyandja, the daughter of Tobit Liyandja. Manassée 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.