Arnoldichthys
Arnoldichthys is characterised by having scales of different sizes, and more teeth than any other member of the Petersiini.
Arnoldichthys is monospecific.
Synonyms
Petersius Boulenger, 1899 (partim)
Type species Arnoldichthys spilopterus
Petersius spilopterus Boulenger, 1909 by original designation of Myers, 1926.
Currently, one species is assigned to the genus Arnoldichthys.
Arnoldichthys spilopterus (Boulenger, 1909)
Type and type locality
Petersius spilopterus Boulenger, 1909: 239, fig. 182. Type locality: “Mouths of Niger, Creek at Atijéré, 80 miles E. of Lagos”. Syntypes: BMNH 1909.7.16.40-41, 1908.12.9.53.
Synonyms
Petersius spilopterus Boulenger, 1909
Arnoldichthys spilopterus Myers, 1926
Common names
Danish: Arnolds tetra/Guinea-karpelaks
English: African red-eyed characin/Arnold's Red-eyed Characin/Arnold's tetra/Niger tetra/Redeye characin (USA), Niger tetra (Global)
Estonian: Aafrika arnoldikala/Arnoldikala
Finnish: Guineantetra/Palettitetra
German: Afrikanischer Großschuppensalmler/Afrikanischer Rotaugensalmler/Arnolds Großschuppensalmler
Polish: Swiecik wielkoluski
Description
Diagnosis: body depth 3.45-3.8 (3.35) and head length 3.5-3.65 (3.35) in the standard length. Prominent upper jaw. Parietal fontanel absent. Dental formula: [8/12-13 (upper jaw), 10-11+6-10 (lower jaw)], [type: 8/10 (upper jaw), 10 (lower jaw)], without any lower internal teeth and non-alternating external premaxillary teeth and numerous teeth in existing rows (see figure below). Diminishing teeth along from the symphysis on both jaws. Cuspids number: upper jaw, external row: 3 to 4; internal row: 3 to 5; lower jaw, external row: 1 to 5. Lower median teeth (10-11) are bigger and with darkened cuspids to their tip, posterior lateral teeth much smaller and non-darkenend. Unpaired fins non-filamentous. Dorsal fin: II,10 (II,10). Anal fin: Ill,11 (III,11). Gill rakers on the lower limb of the first gill arch: 10-11 (10). Predorsal scales larger than the other ones, longitudinal line scales: 30-31+2 (28-30); transversal line scales: 4½ (above lateral line)/ 4½ (below lateral line) (4½/ 3½); 10 scales around the caudal peduncle. Complete lateral line: 30-32 tubes.
Arnoldicthys spilopterus: mouth open in lingual view.
Maximum reported size: 98 mm SL.
Colour: a mid-lateral black band with a light margin over it, continuing on median caudal rays. Lower body surface darkened, dorsal surface darker, the base of the scales is dark too. Dorsal fin with black blotch at the top and in front of the fin. Male with three-coloured anal fin (red, yellow and black margin). Female with a single blotch in the middle of the posterior rays of the anal fin. Greyish caudal fin.
Ecology
A pelagic riverine fish that feeds on worms, insects and crustaceans. In aquaria, female lays up to 1000 eggs, after vigorous driving by the male, which hatch in 30 to 34 hours.
Distribution
Lower Niger and Ogun Rivers, Nigeria (see also Faunafri).
This species is found fewer than 10 locations in Nigeria mainly in a region affected by oil exploration and the other by deforestation. The extent of occurrence and area of occupancy thresholds are estimated at less than 20,000 km² and less than 2,000 km², respectively. As the quality of habitat is also declining it qualifies as Vu B1ab(iii)+2ab(iii). Sub criterion c is not applicable because there is no evidence of extreme fluctuation in EOO or AOO.
Major threats: since there is an extensive aquaria trade in this fish, mainly by wild capture, it can be inferred that the stock may be on a downward trend. This is coupled with deforestation and pollution in it ranges resulting in habitat loss and decline in quality.
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