Auchenoglanis occidentalis (Valenciennes, 1840)

Retzer, Michael E., 2010, Taxonomy of Auchenoglanis Günther 1865 (Siluriformes: Auchenoglanididae), Zootaxa 2655 (1), pp. 25-51 : 44-46

Auchenoglanis occidentalis (Valenciennes, 1840)

( Figs. 7c , 9 , Table 3)

Pimelodus occidentalis Valenciennes, 1840 : in Cuvier & Valenciennes 1840: 203. Type locality: Sénégal. Holotype: MNHN A–8971.

Material examined: Gambia, McCarthy Island : locality unknown, BMNH 1901.12.28.47–48, 2, (209.2– 248.5 mm SL) ; Gambia River, Georgetown, MRAC P–73005.2818, 1, (289.0 mm SL) . Senegal, province and locality unknown, MNHN A–8971, 1, (SL not measured, holotype), Kolda : Casamance River , MRAC P– 73005.2815–16, 2, (148.0–177.0 mm SL) and MRAC P–73005.2817, 1, (261.0 mm SL); Saint-Louis : Doue River, MRAC P–73005.2810, 1, (262.0 mm SL) and MRAC P–73005.2811, 1, (133.7 mm SL); Taoue River, MRAC P–73005.2812-13, 2, (114.6–145.0 mm SL); Gorom River , MRAC P–79002.0211, 1, (141.0 mm SL), Tambacounda : Gambia River, MRAC P–79002.217, 1, (153.0 mm SL), MRAC P–8001.0100, 1, (327.0 mm SL), and MRAC P–89001.0098, 1, (134.1 mm SL) .

Diagnosis: Auchenoglanis occidentalis 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. tchadiensis by adults having uniformly pigmented bodies and fins. Other species of Auchenoglanis lack uniformly pigmented bodies and fins.

Auchenoglanis occidentalis can be distinguished from A. sacchii and A. biscutatus by having a longer preorbital-head length relative to the interorbital distance (PrOL to IOD ratio 1.7–2.0 in A. occidentalis versus 1.3 in A. sacchii and 1.4 in A. biscutatus ). Auchenoglanis occidentalis can be further distinguished from A. biscutatus and A. wittei by having a shorter maxillary-barbel length relative to the head length (MxBL to HL ratio 0.31–0.50 in A. occidentalis versus greater than 0.50 in A. biscutatus and A. wittei ) and by a shorter preorbital-head length relative to the external mandibular-barbel length (PrOL to EMdBL ratio less than 0.9 in A. occidentalis versus greater than 0.9 in A. biscutatus and A. wittei ).

Adults of A. occidentalis can be further distinguished from 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. occidentalis versus over it in A. sacchii . Auchenoglanis occidentalis can be further distinguished from all other Auchenoglanis except A. sacchii (the pigmentation of A. sacchii is only vaguely known from its original description), A. tchadiensis , and A. senegali by its black maxillary barbels and white external and internal mandibular barbels versus all black or brown barbels in A. acuticeps , A. biscutatus , A. tanganicanus , and A. wittei . The oblong-oval premaxillary tooth patches of A. occidentalis separate it from all of the other Auchenoglanis species (except A. acuticeps ) which have either round, square, triangular, or tear-shaped tooth patches ( Fig. 2 ). Adult A. occidentalis can be distinguished from A. biscutatus by having the anterior margins of the nuchal plates straight to slightly curved rather than strongly curved ( Fig. 1a ).

Description: Morphometrics are presented in Table 3. The fins ray counts are as follows: dorsal fin II,6 (1), II,7 (12), II,8 (1); pectoral fin I,7 (1), I,8 (4), I,9 (8), I,10 (1); pelvic fin i,5 (6). The head is large with the dorsal edge in the lateral profile rising steeply from the tip of the snout to the orbit then less steeply to the dorsal-fin origin; the ventral edge is concave or straight from tip of snout to the lower posterior edge 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 noticable 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 slightly concave under the caudal peduncle. In adults the leading lateral edges of the nuchal plates are straight. The leading lateral edges converge to form a blunt point at the anterior end of the first nuchal plate and that plate does not form a notch in the rear edge of the supraoccipital.

The middle rays of the dorsal fin extend 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. The pectoral spine is very stout and serrated on the posterior edge. The distal edge of the pelvic fin is straight with the first 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 of the anal fin is longest. The distal edge of the caudal fin is emarginate.

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 length of the maxillary barbel is shorter than the external mandibular barbel. The length of the internal mandibular barbel is 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 long oblong-ovals.

The color is based on examination of specimens preserved in alcohol. The adult body is uniformly dark brown on the sides of the body and dorsally and light brown ventrally. Juveniles are heavily spotted. The fins of adults are mostly dark but may have vague mottling. The maxillary barbels are very dark but the mandibular barbels are less dark but not white. The sides and top of the head are brown and without spots. The lower side of the head is white or light brown. The upper lip is dark but the the lower lip is less pigmented.

Range: Auchenoglanis occidentalis is restricted to the Senegal, Casamange, and Gambia River Basins of western Africa ( Fig. 9 ).

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 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.

FIGURE 9. Collection localities of Auchenoglanis senegali (black circles) and A. occidentalis (black squares). The triangle denotes the type locality of A. senegali. Symbols may represent multiple collections.