Auchenoglanis tanganicanus Boulenger, 1906

Retzer, Michael E., 2010, Taxonomy of Auchenoglanis Günther 1865 (Siluriformes: Auchenoglanididae), Zootaxa 2655 (1), pp. 25-51 : 37-38

Auchenoglanis tanganicanus Boulenger, 1906

( Figs. 3c , 6 ; Table 2)

Auchenoglanis occidentalis var. tanganicanus Boulenger, 1906: 553 . Type locality: Kalambo , middle of lake, and Mtondwe Bay [Lake Tanganyika]. Syntypes (4): BMNH 1906.9.6.37–38 (2), BMNH 1906.9 .6.39 (1), BMNH 1906.9 .8.69 (1). Teugels, et al. 1991, 511: junior synonym of Auchenoglanis occidentalis (Valenciennes, 1840) .

Material examined: Country unknown: Lake Tanganyika, Kalambo, BMNH 1906.9 .8.37, 1, (301.8 mm SL, syntype) and BMNH 1906.9 .8.38, 1, (325.3 mm SL, syntype); Lake Tanganyika, middle of lake, BMNH 1906.9 .6.39, 1, (293.4 mm SL, syntype); Lake Tanganyika , Mtondwe Bay , BMNH 1906.9 .8.69, 1, (221.0 mm SL, syntype). Burundi: Lake Tanganyika , AMNH 217349 , 1 , (115.0 mm SL); Lake Tanganyika , Usumbura , MRAC P–43821, 1, (243.0 mm SL), MRAC P–90239, 1, (82.8 mm SL), and MRAC P–90240, 1, (180.2 mm SL). Democratic Republic of Congo, Katanga: Lake Tanganyika , Albertville (now Kalemie), BMNH 1955.12 .20.1820, 1, (131.0 mm SL), MRAC P–63768, 1, (304 mm SL), and MRAC P–90244, 1, (175.0 mm SL); Bay of Moba , MRAC P–90237, 1, (500.5 mm SL). Tanzania, Kigoma: Lake Tanganyika , Kanyasa , MRAC P–92081.1887, 1, (198.0 mm SL); Lake Tanganyika , Kigoma Bay , SAIAB 56691 , 1 , (388.2 mm SL); Lake Tanganyika , between Kigoma and Ujiji , SAIAB 56692 , 5 , (182.6–237.7 mm SL) .

Diagnosis: Auchenoglanis tanganicanus can be distinguished from all other Auchenoglanis except A. sacchii (the pigmentation of A. sacchii is only vaguely known from its original description) by its small irregularly shaped spots of various sizes and intensity on the body and the adipose fin of adults. In very large adults (> 300 mm SL), six small but evenly spaced prominent spots occur beginning under the dorsal fin and end on the caudal peduncle just above the lateral line. Each spot is usually paired with a similar spot just above it. The other species of Auchenoglanis lack the small irregularly shaped spots of various sizes and intensity on the body and the adipose fin of adults and in very large adults, the six-paired spots above the lateral line.

Auchenoglanis tanganicanus 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 ) and from A. sacchii , A. biscutatus and A. senegali by having a longer preorbital-head length relative to the interorbital distance (PrOL to IO ratio 1.9–2.3 in A. tanganicanus versus less than 1.3 in A. sacchii and 1.8 in A. biscutatus and A. senegali ). Auchenoglanis tanganicanus can be further distinguished from Auchenoglanis senegali by having a lower minimum caudal-peduncle height relative to the interpelvic distance (MnCPH to IpvD ratio 0.6–0.8 for A. tanganicanus versus greater than 0.8 in A. senegali ).

Adults of A. tanganicanus can be 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. tanganicanus versus over it in A. sacchii . Auchenoglanis tanganicanus can be distinguished from the other Auchenoglanis species except A. biscutatus and A. wittei by its black maxillary barbels and external and internal mandibular barbels versus not all barbels being black. The square premaxillary tooth patches ( Fig. 2c ) of A. tanganicanus further separates it from the oblong-oval, round, triangular, or tear-shaped tooth patches of A. occidentalis , A. acuticeps , A. biscutatus , A. tchadiensis , and A. senegali .

Description: Morphometrics are presented in Table 2. The fin ray counts are as follows: dorsal fin II,6 (1), II,7 (16), II,8 (2); pectoral fin I,8 (2), I,9 (10), I,10 (6), I,11 (1); pelvic fin i,5 (12). 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 to straight from 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 slightly concave at the caudal peduncle. In adults the leading lateral edges of the nuchal plates are straight or slightly curved. The leading lateral edges converge to form a point at the anterior end of the first nuchal plate and that plate notches the rear margin of the supraoccipital.

The middle rays of the dorsal fin extend well beyond the spine and the first and last rays. The dorsal spine is stout and nonserrated on the posterior edge. The pectoral fin is pointed with the first rays much longer than the last rays. 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 its base, and the second or third branched ray of the anal fin is longest. The distal edge of the caudal fin is straight to weakly 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 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 square in shape.

The color is based on examination of specimens preserved in alcohol. The adult body is dark dorsally and laterally but light ventrally. The adults have irregularly shaped brown spots of varying intensity on the body and the adipose fin. In very large adults, six small but evenly spaced prominent spots occur beginning under the dorsal fin and end on the caudal peduncle just above the lateral line. Each of these spots may be paired with a similar spot just above it. The brown spots are present on all of the fins but are less visible in the anal fin and paired fins especially in large specimens. The brown spots on the rayed fins are in an irregular pattern but occasionally form short bands. The barbels and upper lip are dark but the lower lip is lightly pigmented. The proximal end of the barbels is less dark. The sides and top of the head are brown and without spots. The lower side of the head is white.

Range: Auchenoglanis tanganicanus is restricted to Lake Tanganyika ( Fig. 6 ).

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 3. Lateral views of a) Auchenoglanis acuticeps CU 94645, 237.0 mm SL, b) A. wittei MRAC P–57745, 218.0 mm SL, and c) A. tanganicanus SAIAB 56692, 237.7 mm SL.

FIGURE 6. Collection localities of Auchenoglanis tanganicanus (black circles) and A. wittei (black squares). Symbols may represent multiple collections.