Auchenoglanis Günther, 1865

Geerinckx, Tom & Vreven, Emmanuel, 2013, A re-evaluation of the species-level diversity within the catfish genus Auchenoglanis (Siluriformes: Claroteidae), Journal of Natural History 47 (47 - 48), pp. 2979-3010 : 2998-3000

Auchenoglanis Günther, 1865

Pimelodus (partim) La Cepède, 1803

Oxyglanis Vinciguerra, 1898

Replacement name for Auchenaspis Bleeker, 1858 , preoccupied by Auchenaspis Egerton, 1857 ;

type species Pimelodus biscutatus by subsequent designation by Bleeker (1863).

Diagnosis

Auchenoglanis can be easily recognized from the other genera in Auchenoglanidinae using the following straightforward characters: skull roof bones rough and well visible through the skin; supraoccipital process long and (except in small juveniles) almost as broad as the parieto-supraoccipital bone itself, contacting the first nuchal plate that often overlaps it slightly; very well-developed nuchal plates visible as one unit, lying broadly C-shaped around the base of the dorsal fin (except in small specimens, where they are triangular); eyes lateral, with free border and housed in well-defined bony orbits; premaxillary tooth plate composed of two tear-shaped to rectangular patches (premaxillae), each longer than broad, often not touching; minimal caudal peduncle depth 41–58 (63) % of head depth (measured at the level of the supraoccipital process) (larger than 56% in the other genera).

Description

Auchenoglanis is further characterized by: 9–11 branchiostegal rays; branchiostegal membranes not fused; dorsal fin with two spines (the first is short and inconspicuous) and 7 branched rays, pectoral fin with one spine and (8)9–10 branched rays (other genera 5–8), pelvic fin with 6 rays (5 of which are branched), anal fin with 9–13 rays (6–8 branched); edge of caudal fin (slightly) forked. Auchenoglanis shares with the other subfamily members the tube-like anterior nostrils, situated on the upper lip, and presenting the most straightforward diagnostic trait for the subfamily.

Osteology

Anterior bifurcation of mesethmoid rudimentary; minute tips pointing rostrally. Anterior fontanelle spindle-shaped or slightly drop-shaped, with narrower anterior end; mesethmoid bordering only the far anterior end of the fontanelle. No posterior fontanelle. Superficial face of lateral ethmoid very elongated. Nasal bones long and very narrow tubes. Frontals not narrowing at the level of the eyes. Infraorbital canal entering the sphenotic well away from the suture with the frontal. Number of infraorbital bones varying from four to six. Next-to-last infraorbital often, and last infraorbital always medially curved. Orbita round and well demarcated by lateral ethmoid, frontal, sphenotic, and last two infraorbitals. Antorbital large and elongate, with a posterior plate-like portion. Parieto-supraoccipital broadly wedge-shaped anteriorly, deeply projecting between frontals. Supraoccipital process massive: as long as the body of the parieto-supraoccipital bone itself, and almost equally broad at its base.

Dentary with anterior flange near symphysis; coronoid process short, robust, not reclining posteriorly. Posterolateral autopalatine flange long but not deep. Metapterygoid and hyomandibular almost without direct contact, due to long symplectic cartilage. Hyomandibular without dorsal ridge or process.

Dorsoposterior and humeral processes of cleithrum distinct. Well-developed first nuchal plate usually somewhat overlapping the supraoccipital process. Second and (paired) third nuchal plates also well developed, well visible through the skin. Supraneural well developed. Space between anterior and posterior branches of parapophysis of fourth, complex vertebra almost completely filled by a bony sheet. Total number of 47 vertebrae (based on one cleared and stained specimen per species; see Material and methods). This number includes the anterior complex vertebral centrum (counted as 4; Chardon et al. 2003). These characters allow discrimination from other claroteid genera. Refer to Teugels et al. (1991) and Geerinckx et al. (2013) for comparative morphological and osteological data of other auchenoglanidine genera.

The genus already existed at least 7 million years ago, as reports on the fossil Auchenoglanis soye from West Central Chad indicate ( Otero et al. 2007). Fossil pectoral spines dated about 37 million years old ( Murray et al. 2010) were assigned to Auchenoglanis as well ( Gayet & Van Neer 1990). Its recent distribution is quite wide. Auchenoglanis biscutatus is found from West African basins up to the Nile (holotype and recent, confirmed record from the Nile at Kosti, Sudan), with confirmed records as far east as Lake Turkana (personal communication Radim Blažek 2012). Auchenoglanis occidentalis , having a range that covers the A. biscutatus distribution and stretches south to the Congo basin, Lake Tanganyika and isolated Lake Rukwa, ranks among the most widespread African fish species, along with species such as Clarias gariepinus and Micralestes acutidens ( Skelton 1988; Rognon et al. 1998). Cryptic diversity cannot be excluded, and genetic studies like those done by Ozouf-Costaz et al. (1990) for C. gariepinus could help verify the current taxonomic status.

Both Auchenoglanis species appear to be rather resilient, as they are found in a variety of habitats and have been reported to be omnivorous, feeding on arthropods and other invertebrates, fish, detritus and plant material ( Blache et al. 1964; Latif 1974; Lewis 1974). Both species are known as migratory, spawning in flooded areas during the rainy season, often being found more in floodplains and marshy zones than in main river channels ( Copley 1958; Blache et al. 1964), and could therefore possibly quite easily reach new river basins when temporary contacts between basins arise. Migration along river basins in the arid Sub-Saharan region may have been substantially easier in the past. Past connections, like those between the Omo-Turkana and Nile systems, until approximately 7500 years ago ( Greenwood 1976; Beadle 1981), may explain, for example, the presence in the now isolated Lake Turkana basin of both A. occidentalis ( Oxyglanis sacchii holotype) and A. biscutatus (personal communication Radim Blažek 2012), pictures of which show no notable difference from the A. biscutatus records from other basins.

Key to species in Auchenoglanis

1. Horizontal distance between eye and end of supraoccipital process larger (104% or more) than horizontal distance between snout tip and eye ( Figure 1C ); adipose fin rising abruptly; tip of maxillary barbel not darker than head................................................... A. biscutatus Horizontal distance between eye and end of supraoccipital process equal, or smaller (100% or less) than horizontal distance between snout tip and eye; adipose fin rising very gradually; maxillary barbel tip darker than head................................................................. A. occidentalis

Figures

Figure 1. (A) Plot of principal components two and three (with percentage of total variance) of 31 log-transformed biometric data for 168 Auchenoglanis specimens; (B) plot of principal components two and three of 27 log-transformed biometric data for 168 Auchenoglanis specimens (all three barbel lengths, and combined premaxillary tooth plate width omitted); (C) ratio of postorbital to preorbital head length plotted against head length (measured until end of supraoccipital process) for 169 Auchenoglanis specimens. Type specimens are indicated by large symbols. For the A. biscutatus group: black circle: A. biscutatus holotype; grey circles: A. senegali types. For the A. occidentalis group: black triangle: A. occidentalis holotype; white triangles: A. o. tanganicanus types; white inverted triangles: A. acuticeps types; grey triangles: A. o. tchadiensis types; grey inverted triangles: A. wittei types. The Oxyglanis sacchii holotype is not included because its bad, dried state compromised many measurements.