Nannocharax usongo, Dunz, Andreas R. & Schliewen, Ulrich K., 2009

Dunz, Andreas R. & Schliewen, Ulrich K., 2009, Description of two new species of Nannocharax Günther, 1867 (Teleostei: Characiformes: Distichodontidae) from the Cross River, Cameroon, Zootaxa 2028, pp. 1-19 : 10-13

Nannocharax usongo , new species

( Figure 5 a–c, Table 4)

Holotype. ZSM 35732 (1, 44.2 mm SL); Cameroon, Cross River at Mamfé, collected by U. Schliewen, February 2002.

Paratypes. ZSM 35733 (8, 25.0– 40.4 mm SL); same collection data as holotype. MRAC 88-53- P- 116- 128 (13, 20.6–29.6 mm SL); Cross Basin, riffles in outlet of Badi River into Cross River and Cross River at Mamfé, (5°46’ N, 9°17’ E), collected by T.R. Roberts, 1-5 March 1980.

Additional material: MRAC 87-24- P- 88, (1, 34.0 mm SL); Nigeria, Sombreiro River at Ihuaba, Niger delta (5°1’ N, 6°40’ E), collected by C.B. Powell, 24 March 1987.

Diagnosis. Nannocharax usongo is distinguished from all other described Nannocharax species by its very small distance between the posterior border of the anus and the articulation of first anal-fin ray (0.9–1.9 vs. 2.2–14.2% of SL), its body coloration, which consist of 7–11 mostly big blotches along the lateral line often coalesced to one wide black band, and 7–12 small blotches along the dorsum.

Description. Morphometric and meristic data of holotype and 21 paratypes are presented in Table 4. See Figures 5 a & b for general appearance. Nannocharax usongo is a medium-sized species (maximum size observed 44.2 mm SL). Body elongate, sides slightly compressed, greatest body depth at anterior dorsal-fin region. Predorsal body profile slightly convex to snout. Body profile at base of dorsal fin slightly posteroventrally sloped. Dorsal body profile posterior to dorsal fin convex to adipose fin, from there straight to caudal peduncle. Ventral body profile straight or very slightly posterodorsally sloped from tip of lower jaw to base of pectoral-fin and from pectoral fin insertion nearly straight to insertion of anal fin. Body profile at base of anal-fin base slightly posterodorsally inclined. Ventral body profile posterior to anal fin slightly posterodorsally sloped to caudal peduncle. Caudal peduncle length about 15% of SL. Body depth at anal-fin end located at the vertical distance between posterior base of anal fin and adipose fin. Head pointed in dorsal view. Eyes large and situated closer to the tip of the snout than to the posterior end of operculum. Eye diameter always smaller than interorbital width. Snout length smaller than interorbital width. Nostrils closer to the anterior border of the eye than to the tip of snout. Mouth small and subterminal. Body covered with ctenoid scales. Lateral line complete and originating midlaterally behind operculum. Two or three lateral line scales extending of on caudal fin.

Fins. Origin of dorsal fin located approximately on vertical through posterior end of pelvic-fin base. Length of dorsal-fin base short, first ray unbranched and sometimes very short. Dorsal rays 10 in holotype and 10–13 in paratypes. Length of adipose-fin base very small (2.7–3.9% of SL) and located approximately on the vertical through posterior end of anal-fin base. Caudal fin forked with equal-sized lobes. Length of anal-fin base nearly equal in length as dorsal-fin base (10.5–13.4% of SL). Anal rays 11 in holotype, 10–12 in paratypes, sometimes first ray very small. Pelvic-fin rays 8 in holotype, 8 or 9 in paratypes, third pelvic ray always longest. First, second and third ray very thick in comparison with all other pelvic rays. Pelvic-fin rays well developed. Tip of longest pelvic-fin ray not reaching anus. Anus clearly visible. Pectoral-fin rays 15 in holotype (13–16 in paratypes). Tip of longest pectoral-fin ray reaching posterior pelvic-fin base.

Dentition. Upper jaw with a single row of 10 bicuspid, acute teeth in holotype, 8–10 in paratypes. Upper jaw teeth limited to the premaxilla.

Coloration in alcohol. Ground coloration pale brownish, with several scattered dark melanophores in holotype and paratypes. Melanophore concentration higher on dorsal region and flanks than on ventral side. Melanophores mainly located on borders of scales. Region around nostrils and lips unpigmented. Ventral surface of head ranging from unpigmented to having scattered, small, dark melanophores. Dorsal surface of head strongly pigmented up to the minimum interorbital distance. Surface of snout greyish. Infraorbital area irregularly pigmented. Anterior part of operculum with a many melanophores. Area around anus unpigmented. Body covered with usually 7–11 mostly big round blotches along lateral line, often coalesced to one wide black band. 7–12 small blotches along dorsum often coalesced to a dark band. This band terminates mostly at the level of insertion of pelvic fin. Some paratypes with narrow vertical bars along lateral line at predorsal body region. In some specimens blotches embedded in a wide dark band. At level of anus a semicircular area with only a few melanophores interrupts the wide band. A large blotch embedded in band always well visible on caudal peduncle. A small dark round blotch at the insertion of pelvic fin as well as at the insertion of pectoral fin. Dorsal fin coloration ranging from a dark blotch at the insertion of the first rays to a dark band on all rays at their base. Band posteroventrally sloped. Tip of the first dorsal rays coloured with small spots. Adipose fin without coloration. Caudal fin on each lobe with a distally situated narrow dark band, the two bands are at the same level. Ventral lobe always with a lenticular blotch often connected with the blotch at caudal peduncle. Dorsal caudal-fin lobe with a weakly visible band at the same level of as the blotch on the lower lobe. Anal fin coloration similar to dorsal-fin coloration, but not distinct. Small marks at the tips of the first rays usually absent. Pelvic fin coloration ranging from unpigmented to narrow dark band mainly at the thicker rays. Pectoral fin without coloration, only a few melanophores present.

Coloration in life. All areas except the dorsum reported as dark or black in the description of coloration in alcohol are emerald-green, mainly the operculum ( Fig. 5 c).

Distribution. All examined samples of Nannocharax usongo were collected in the Cross River basin, riffles in outlet of the Badi River into the Cross River and the Cross River at Mamfé in Cameroon at a distance of less than one mile north of outlet of the Badi River. One additional albeit slighty aberrant specimen (see below) was collected in the Sombreiro River at Ihuaba, Niger River delta Nigeria.

Etymology. Named in honor of Dr. Leonard Usongo , highly successful conservation biologist and supporter of numerous fish inventories in Cameroon. A noun in apposition.

Ecological notes. Type specimens were collected on logs in areas of relatively rapid water movement while snorkeling. These had a very rugged surface due to being partially decomposed by wood eating Povilla (Ephemeroptera) larvae. Individuals were spaced singly and moved very rapidly around the log surface, but always with close contact to it and never reaching out into the free water column.

Remarks on special specimen. Possibly specimen MRAC 87-24-P-88 ( Fig. 6 & Table 4) from the Sombreiro River at Ihuaba, Niger River delta is conspecific with Nannocharax usongo . There are only few differences in body shape and coloration.

Figures

FIGURE 5. Holotype of Nannocharax usongo sp. nov. (ZSM 35732), 44.2 mm SL, Cameroon, Cross River at Mamfé, a. Photograph of holotype showing preserved coloration in alcohol, b. Illustration of, drawing by R. Kühbandner, c. Photograph of live specimen of N. usongo (Photo F. Herder).

FIGURE 6 Nannocharax usongo, MRAC 87 - 24 - P- 88, 34.0 mm SL, Nigeria, Sombreiro River at Ihuaba, Niger delta, preserved coloration in alcohol.