Auchenoglanis tchadiensis Pellegrin, 1909

Retzer, Michael E., 2010, Taxonomy of Auchenoglanis Günther 1865 (Siluriformes: Auchenoglanididae), Zootaxa 2655 (1), pp. 25-51 : 38-39

Auchenoglanis tchadiensis Pellegrin, 1909

( Figs. 4 , 7a ; Table 2)

Auchenoglanis occidentalis tchadiensis Pellegrin, 1909: 244 . Type locality: Lac Chad Bol. Syntypes: MNHN 1909–0425 (3), MNHN 1909–0426 (4). Teugels, et al. 1991, 511: junior synonym of Auchenoglanis occidentalis (Valenciennes, 1840) .

Material examined: Cameroon, Extreme North: Logone River, Yagoua , MRAC P–73016.5489, 1, (209 mm SL) . Central African Republic, Bamingui-Bangoram: Koumbala River, AMNH 228630 , 1 , (175 mm SL); Vakaga River , AMNH 228740 , 4 , (96.2–120.7 mm SL), Ouaudja and Vakaga Rivers ; AMNH 230612 , 1 , (126.1 mm SL), Bamingui River , AMNH 230726 , 1 , (310 mm SL); Gounda River , MRAC P–82021.0738- 040, 3, (89.3–145.8 mm SL) . Chad, Hadjer-Lamis: Lake Chad at Bol, MNHN 1909-0425 - 0426 , 8 , (photos, SL not measured, syntypes); Salamat: Tinga River or Lake, MRAC P–154047, 1, (205 mm SL) .

Diagnosis: Auchenoglanis tchadiensis can be distinguished from all other Auchenoglanis except A. sacchii (the pigmentation of A. sacchii is only vaguely known from its original description) and A. occidentalis by adults having uniformly pigmented bodies. Other species of Auchenoglanis do not have uniformly pigmented adult bodies.

Adult A. tchadiensis can be further distinguished from A. biscutatus by having the anterior margins of the nuchal plates straight to slightly curved rather than strongly curved ( Fig. 1a ). Auchenoglanis tchadiensis can be further distinguished from A. wittei by having a shorter maxillary-barbel length relative to the head length (MxBL to HL ratio 0.31–0.49 in A. tchadiensis versus greater than 0.53 in A. wittei ).

Adults of A. tchadiensis can be further distinguished from adult A. biscutatus and A. senegali by having the anterior edge of the adipose fin that rises gradually to its maximum height at the posterior end of the fin, well behind the mid-point of the adipose fin versus the anterior edge of the fin that rises steeply and reaches its maximum height at a point approximately one half of the length of the adipose fin. The origin of the adipose fin is before the anal-fin origin in A. tchadiensis versus over it in A. sacchii . Auchenoglanis tchadiensis can be further distinguished from all other Auchenoglanis except A. sacchii , A. occidentalis , and A. senegali by its black or brown maxillary barbels and white external and internal mandibular barbels versus all black or brown barbels. The triangular premaxillary tooth patches ( Fig. 2e ) of A. tchadiensis separate it from the oblong-oval, round, square, or tear-shaped tooth patches of all the other species of Auchenoglanis .

Description: Morphometrics are presented in Table 2. The fin ray counts are as follows: dorsal fin II,6 (1), II,7 (11); pectoral fin I,8 (7), I,9 (5); pelvic fin i,5(8), i,6 (1). The head is large with the dorsal edge in the lateral profile rising steeply from the tip of the snout to the dorsal-fin origin; the ventral edge is straight from the tip of snout to the lower posterior margin of the opercle. Body depth is greatest at the dorsal-fin origin. The dorsal-lateral profile descends less steeply from the dorsal-fin origin to the caudal peduncle with a slight rise and descent under the adipose fin. The minimum caudal-peduncle height is at the posterior edge of the base of the adipose fin. The ventral-lateral profile from the rear of the head to the anal fin is flat and concave at the caudal peduncle. In adults the leading lateral edges of the nuchal plates are straight or slightly curved ( Fig. 1a ). The leading lateral edges converge to form a point at the anterior end of the first nuchal plate and that plate does not notch the rear margin of the supraoccipital.

The middle rays of the dorsal fin extend somewhat beyond the spine and the first and last rays. The dorsal spine is stout and nonserrated on the posterior edge. The distal edge of the pectoral fin is straight to slightly convex. The pectoral spine is stout and serrated on the posterior edge. The distal edge of the pelvic fin is convex with the second branched ray being the longest ray. The rays of the anal fin are much longer than the base, and the second or third branched ray is longest. The distal edge of the caudal fin is round to weakly emarginated.

The pectoral fin is placed approximately on the anterior one-quarter of the body, well ahead of the dorsalfin origin. The pelvic fin is placed behind the dorsal-fin origin. The anal fin is placed approximately on the posterior one-third of the body.

The maxillary barbel is approximately three-quarters of, to equal to, the length of the external mandibular barbel. The internal mandibular barbel is much shorter than the other barbels. The maxillary and external mandibular barbels are slender, but the internal mandibular barbel is thicker particularly at the base. The lower lip is thick.

The mouth is subterminal and narrow relative to the head width. The premaxillary tooth patches are triangular in shape.

The color is based on examination of specimens preserved in alcohol. The adult body is uniformly brown on the sides of the body and dorsally and white ventrally. Some vague mottling may be present. The mottling is more apparent in juveniles. The dorsal, adipose, and caudal fins have indistinct spots that sometimes fuse to form indistinct bands. The other fins are plain or with very faint mottling. The maxillary barbel is darkly pigmented and the mandibular barbels are white or slightly brown. The sides and top of the head are brown and without spots. The lower side of the head is white.

Range: Auchenoglanis tchadiensis is restricted to the Lake Chad basin ( Fig. 4 ).

Figures

FIGURE 1. Diagrams of nuchal plate patterns of Auchenoglanis. a) leading edge straight, b) leading edge curved. The arrow indicates the anterior end of the plates. The numbers indicate individual plates.

FIGURE 2. Diagrams of the five types of premaxillary tooth patches of Auchenoglanis. a) oblong-oval, b) round, c) square, d) tear, and e) triangle. The arrow indicates the direction of the anterior end of the patches.

FIGURE 4. Collection localities of Auchenoglanis acuticeps (black squares), A. biscutatus (black triangles), A. sacchii (open circle), and A. tchadiensis (black circles). Symbols may represent multiple collections.

FIGURE 7. Lateral views of a) Auchenoglanis tchadiensis MRAC P–154047, 205 mm SL, b) A. biscutatus modified from Boulenger (1907), and c) A. occidentalis MRAC P–73005.2810, 262.0 mm SL.