The giraffe catfishes are more diverse than previously thought, with a revisionary study published in the most recent issue of the journal Zootaxa recognising eight valid species of Auchenoglanis, one of which is described as new.
The study by Michael Retzer revalidates five species previously considered junior synonyms of either Auchenoglanis biscutatus or A. occidentalis in an older revisionary study published in 1991.
The species are largely distinguished from each other by their colour pattern, proportions of the head and barbels, the shape of the nuchal plates (these are bony plates located in front of the dorsal fin), adipose fin and tooth patches on the upper jaw, and the colour of the barbels.
One new species (A. senegali) is described in this study.
Auchenoglanis acuticeps
This species has small round spots in a regular pattern on the body, adipose fin, caudal and dorsal fins. Previously considered a synonym of A. occidentalis, this species is known from Lake Albert to the lower Nile.
Auchenoglanis biscutatus
This species is distinguished from congeners in having the body and adipose fin in adults light brown or grey and with small, distinct spots on the rayed fins that do not coalesce to form bands. The shape of the nuchal plate is also very distinctive for this species and separates it from all other congeners. This species is restricted to the Nile River drainage.
Auchenoglanis occidentalis
This species is distinguished from congeners except A. tchadiensis in having a uniformly-coloured body. It differs from A. tchadiensis in having oval-shaped (vs. triangular) tooth patches on the upper jaw. This species is restricted to the Senegal, Casamange, and Gambia river drainages in western Africa.
Auchenoglanis sacchii
In this species the origin of the adipose fin is at the same vertical level as the origin of the anal fin (all other species have the origin of the adipose fin in front of the origin of the anal fin). Previously considered a synonym of A. occidentalis, this species is known only from the Omo River drainage in Ethiopia.
Auchenoglanis senegali
This new species is distinguished from congeners in having three horizontal series of dark spots on the body and intense dark spots on the fins, and tear-shaped tooth patches on the upper jaw. This species is known only from the Senegal and Gambia river drainages in western Africa.
Auchenoglanis tanganicanus
This species is distinguished in having small, irregularly shaped spots of various sizes and intensity on the body and the adipose fin of adults. Furthermore, very large adults larger than 30cm/12" standard length possess six small but evenly-spaced prominent spots beginning under the dorsal fin and ending on the caudal peduncle just above the lateral line. Previously considered a synonym of A. occidentalis, this species is known only from Lake Tanganyika.
Auchenoglanis tchadiensis
Distinguished from congeners except A. occidentalis in having a uniformly-coloured body. It differs from A. occidentalis in having triangular (vs. oval-shaped) tooth patches on the upper jaw. Previously considered a synonym of A. occidentalis, this species is known only from the Lake Chad drainage.
Auchenoglanis wittei
This species has medium, irregular-shaped spots in a reticulated pattern on the body of adults. Previously considered a synonym of A. occidentalis, this species is known from the central Congo River drainage.
The study also recognises further diversity in the genus (in the form of more unnamed species in the genus), with populations from western Africa and Lake Rukwa (in Tanzania) identified as unnamed species.
For more information, see the paper: Retzer, ME (2010) Taxonomy of Auchenoglanis Günther 1865 (Siluriformes: Auchenoglanididae). Zootaxa 2655, pp. 25–51.