Bathyaethiops baka, Moritz, Timo & Schliewen, Ulrich K., 2016

Moritz, Timo & Schliewen, Ulrich K., 2016, Description of two new Bathyaethiops species (Teleostei: Alestidae) from the Congo basin, Zootaxa 4117 (4), pp. 476-490 : 477-481

Bathyaethiops baka , new species

Dwarf Moon Tetra

( Figs. 1–2 ; Tables 1–2 )

Type material. Holotype: ZSM 43939, 24.1 mm SL, male; Cameroon, Moloundou province: Ngoko River between Chûte de Cholet and Chûte de Nki (N 02°19’10’’, E 14°28’15’’); coll: J. Schwarzer & T. Moritz, 10.02.2008.

Paratypes (n=15): DMM IE/9789, 2 specimens, 20.5–23.2 mm SL, same data as holotype; ZSM 38450, 1 specimen, 23.0 mm SL, same data as holotype; AMNH 265019, 3 specimens, 19.8–21.2 mm SL, Cameroon, Moloundou province: Ngoko River below Chûte de Nki; coll. J. Schwarzer & T. Moritz, 09.02.2008; ZSM 43940, 3 specimens, 20.3–21.6 mm SL, Cameroon, Moloundou province: Ngoko River below Chûte de Nki; coll. J. Schwarzer & T. Moritz, 09.02.2008; ZSM 38454, 1 specimen, 22.1 mm SL, Cameroon, Moloundou province: Ngoko River at Ndongo (N 02°06’40’’, E 14°52’42’’); coll. J. Schwarzer & T. Moritz, 04.02.2008; MRAC B5-023- P-0004-0006, 3 specimens, 21.5–23.7 mm SL Cameroon, Moloundou province: Ngoko River at Ndongo (N 02°06’40’’, E 14°52’42’’); coll. J. Schwarzer & T. Moritz, 05.02.2008; ZSM 43941, 2 specimens, 23.3–24.4 mm SL, Cameroon, Moloundou province: Ngoko River at Ndongo (N 02°06’40’’, E 14°52’42’’); coll. J. Schwarzer & T. Moritz, 0 5.02.2008.

Additional material. ZSM 38453, 6 specimens, same data as holotype; ZSM 38456, 3 specimens, Cameroon, Moloundou province: Ngoko River at Ndongo; coll. J. Schwarzer & T. Moritz, 0 3.02.2008 ZSM 43942, 6 specimens, Cameroon, Moloundou province: Ngoko River at Ndongo; coll. J. Schwarzer & T. Moritz, 05.02.2008; ZSM 43943, 15 specimens, Cameroon, Moloundou province: Ngoko River at Ndongo; coll. J. Schwarzer & T. Moritz, 08.02.2008; ZSM 43944, 8 specimens, Cameroon, Moloundou province: Ngoko River below Chûte de Nki; coll. J. Schwarzer & T. Moritz, 09.02.2008; DMM IE/9792, 1 c&s, Cameroon, Moloundou province: Ngoko River below Chûte de Nki; coll. J. Schwarzer & T. Moritz, 09.02.2008;

Differential diagnosis. Distinguished from all congeners by an incomplete squamation with the scale cover variably reduced to no pre-dorsal scales, usually no scales on caudal peduncle, and usually a scale-free patch on middle flank at about level of pelvic-fin origin. Furthermore distinguished by a unique color pattern, i.e., a combination of a humeral spot of about pupil-size and the absence of dark vertical bars along midlateral flanks.

Difficult to distinguish from juvenile B. caudomaculatus , from which the new species differs by the (usually) absence of unicuspid teeth in the second row of lower jaws (vs. presence), and (usually) the absent or rudimentary supraneural between two neural spines directly in front of the first dorsal fin pterygiophore (vs. well developed).

Description. Based on holotype and 15 paratypes. For general appearance refer to Figs. 1 and 2 . Measurements and meristics summarized in Tables 1 and 2. A comparatively small species, maximum size 24.4 mm SL. Body laterally compressed, slightly elevated. Dorsal fin originating midway along body; pelvic fins originating slightly in front of dorsal fin; anal fin originating approximately at level of end of dorsal-fin base; adipose fin originating at level of caudal end of anal-fin base, positioned closer to caudal than to dorsal fin. Scale cover variably reduced: no pre-dorsal scales; usually no scales on caudal peduncle; usually a scale free patch on middle of flank at level of pelvic-fin origin. Number of pored scales in lateral line variable (0–9); lateral line never complete.

Premaxilla with two teeth in outer row, each with three major and two minor cusps and four teeth in inner row with four cusps in the first, six cusps in the second and third, and seven cusps in the last tooth ( Fig. 3 ). Dentary with four teeth in outer row, each with six cusps, except the last with only five cusps ( Fig. 3 ); an inner single monocuspid tooth usually absent (where it was possible to check this character without damaging the specimen only 2 out of 12 had inner monocuspid teeth). Anal fin convex in males ( Figs 1 , 2 ), but almost straight in females and juveniles. Pectoral fin with 12 rays with dorsalmost and ventralmost rays unbranched. Pelvic fin with 8 rays, with first and last rays unbranched. 2 hypurals in lower lobe and 4 hypurals in upper lobe; 3 epurals; small cartilage present in front of anterior-most haemal spine. Other fin and vertebrae counts presented in Table 2. Supraneural directly in front of first pterygiophore of dorsal fin reduced in size or absent.

This species seems to be a dwarf species within the genus Bathyaethiops . Juveniles of this species and juvenile sympatric B. caudomaculatus are difficult to differentiate.

Coloration. In life ( Fig. 2 ) body pale translucent; dorsal, adipose and caudal fin bright red; pelvic and anal fin light orange to yellow; pectoral fin yellowish; upper quarter of iris orange; caudal peduncle on its dorsal and ventral margin slightly red. A prominent humeral spot the size of the pupil or larger, and a slightly larger dark spot on the caudal peduncle; the latter is bisected by a dark line along the midlateral line starting slightly in front of dorsal-fin origin and terminating just distal to the caudal peduncle spot; never any vertical stripes or barring along the midlateral line. Few melanophores in mid-dorsal line along the back starting on lower jaw and reaching caudal peduncle; thin line of melanophores along anal-fin base; often an elevated line of melanophores proximal to the anal-fin base; a dark bar at the end of the caudal peduncle. Melanophores densely set on posterior dorsal half of head. In general, contrast and coloration more pronounced in mature males.

In preservative ( Fig. 1 ) pale whitish to light brown; red, orange and yellow coloration absent. Melanophore pattern as in preserved specimens, but spot on the caudal peduncle less pronounced and smaller, i.e. not reaching the anal fin base; humeral spot more intensively colored but of same size.

Etymology. Named after the Baka people, the native hunter-gatherer tribe in Southeastern Cameroon, where the species was found. A noun in aposition.

Distribution and habitat. The species is so far known from several localities along the Ngoko River, from below the Nki falls to the village of Ndongo ( Fig. 4–5 ). The Ngoko, called Dja River above the Nki falls, is a tributary to the Sangha River, a major northern tributary of the Congo River. All specimens were caught in the main river channel, usually in or close to riparian vegetation over a substrate of fine particles and organic material. Water parameters from the Ngoko River at Ndongo taken on 0 4.02.2008 were: pH 7.08; conductivity 23 µS; temperature 27.5°C.

Meristic character Holotype Paratypes (N=15) Simple dorsal fin rays 3 2 (15)

Branched dorsal fin rays 8 8 (15)

Simple anal fin rays 3 3 (15)

Branched anal fin rays 21 18 (1); 19 (5); 20 (7); 21 (1); - (1) Upper procurrent caudal fin rays 9 5 (1); 6 (5); 7 (5); 8 (4) Upper principal caudal fin rays 10 10 (13); 11 (2)

Lower principal caudal fin rays 9 9 (14); 10 (1)

Lower procurrent caudal fin rays 7 5 (4); 6 (10); 7 (1) Vertebrae 37 35 (1); 36 (11); 37 (3) Abdominal vertebrae 16 16 (4); 17 (10); 18 (1) Caudal vertebrae 21 19 (10); 20 (5)

Dorsal fin inserting after vertebra 10 10 (10); 11 (5)

Anal fin inserting after vertebra 17 17 (10); 18 (5)

Supraneurals 6 6 (7); 7 (7); 8 (1); Pored scales in LL* 5 0 (1); 5 (6); 6 (5); 7 (2); 9 (1)

Figures

FIGURE 1. Bathyaethiops baka sp. nov., holotype, ZSM 43939; 24.1 mm SL; Ngoko River below Nki falls; Cameroon.

FIGURE 2. Bathyaethiops baka sp. nov., live male directly after capture (08. February 2008) at Ngoko River below Nki falls; Cameroon.

FIGURE 3. Dentition of Bathyaethiops baka sp. nov., non-type material, DMM IE / 9792, 21.1 mm SL. A—single teeth in distal view. B—jaws in occlusal view.

FIGURE 4. Records of Bathyaethiops species; filled symbols—localities where specimens where checked by Mamoneke & Stiassny (2012) or in the present study; symbol outlines—other records from MRAC database; T—type localities; star— B. atercrinis, cross— B. baka, circle— B. caudomaculatus, inverse triangle— B. flammeus, triangle— B. greeni,, square— B. breuseghemi.

FIGURE 5. Ngoko River between Nki falls and Ndongo (approx. N 02 ° 04 ’ 23 ’’, E 14 ° 49 ’ 52 ’’); Cameroon.

Tables

TABLE 1. Morphometric characters for Bathyaethiops baka n. sp. from Ngoko River. Range, mean and SD (= standard deviation) include paratypes (N = 15) and holotype.

Morphometric characters	Holotype	Range	Mean	SD
Standard length (SL) in mm	24.1	19.8–24.4	24.4	-
in %SL
Body depth in front of dorsal fin	32.8	29.0–33.5	33.5	1.34
Head length (HL)	27.4	24.6–31.5	26.9	1.49
Pre-dorsal length	53.2	50.9–56.2	54.4	1.44
Pre-anal length	65.3	63.9–69.6	66.0	1.39
Pre-pectoral length	26.7	23.3–34.3	26.3	2.37
Pre-ventral length	47.9	43.3–50.7	47.6	2.14
Pre-adipose length	87.9	85.9–91.3	87.6	1.14
Distance dorsal fin to adipose fin	22.3	19.6–23.0	21.6	0.87
Dorsal fin base	13.5	11.4–13.6	12.4	0.53
Longest dorsal fin ray	29.2	24.2–32.0	29.4	1.92
Anal fin base	28.5	22.8–28.5	25.9	1.44
Longest anal fin ray	12.2	7.6–14.3	11.5	2.08
Caudal peduncle length (CPL)	9.9	6.4–10.2	8.6	1.09
Caudal peduncle depth (CPD)	9.2	7.6–11.1	9.25	0.95
in %HL
Snout length	19.1	15.0–24.7	19.0	2.18
Eye diameter	45.7	38.6–48.1	44.5	2.55
Postorbital length	29.5	28.6–36.0	31.8	2.20
Interorbital distance	31.8	27.7–38.7	32.1	2.78
Head width	48.7	41.2–53.7	48.4	3.13
Head height at eye	72.5	57.5–72.5	67.7	3.33
CPD in %CPD	107.2	58.2–126.1	94.4	17.45