Nannocharax zebra, 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 : 5-10

Nannocharax zebra , new species

( Figure 3 a & b; Table 3)

Holotype. ZSM 35730 (29.1 mm SL); Cameroon, Cross River at Mamfé, collected by U. Schliewen, February 2002.

Paratypes. ZSM 35731 (4, 28.5–32.5 mm SL); collection data as for holotype. MRAC 88-53- P- 129-153 (25, 25.0– 39.3 mm SL); Cross River 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 non-type material: MRAC 87-24- P- 87 (1, 40.7 mm SL); Nigeria, Sombreiro River at Odieke (5°8’ N, 6°41’ E), collected by C.B. Powell, 7 January 1986.

Diagnosis. Nannocharax zebra is distinguished from all other described Nannocharax species except N. schoutedeni , N. latifasciatus , N. ansorgii and N. procatopus , by its shorter distance between posterior border of anus and articulation of first anal-fin ray (2.2–3.8 vs. 4.2–14.2% of SL). It differs from N. schoutedeni by having 39–43 vs. 36 or 37 lateral line scales, from N. latifasciatus by its major depth of caudal peduncle (55.9–63.8% vs. 48.1–50.8% of SL), from N. ansorgii by having 12–13 rather than 9 anal-fin rays, and from N. procatopus by having a lower caudal peduncle length (11.3–15.2% versus 18.0%), by having 39–43 rather than 36 lateral line scales.

Description. Morphometric and meristic data of the holotype and 29 paratypes are presented in Table 3. See Figures 3 a & b for general appearance. Nannocharax zebra is a medium-sized species (maximum size observed 39.3 mm SL). Body elongate, sides slightly compressed, greatest body depth at anterior dorsal-fin region. Predorsal body profile slightly convex. Body profile at base of dorsal fin slightly posteroventrally sloped. Dorsal body profile posterior to dorsal fin 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 straight to caudale peduncle. Caudal peduncle length more than 10% of SL. Body depth at anal-fin end is 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 the operculum. Eye diameter always greater than interorbital width. Snout length equals interorbital width. Nostrils closer to anterior border of eye than to tip of snout. Mouth small and subterminal. Body covered with ctenoid scales. Lateral line complete and originating midlaterally behind operculum. Two Fins. Origin of dorsal fin on level with origin of pelvic fin. Length of dorsal-fin base short and first ray usually unbranched and very short. Dorsal rays 12 in holotype and 12–14 in paratypes. Length of adipose-fin base very short and located approximately on the vertical through posterior end of anal-fin base. Caudal fin deeply forked with equal-sized lobes. Length of anal-fin base nearly equals length of dorsal-fin base. Anal rays 12 in holotype and 12 or 13 in paratypes, sometimes first ray very small. Pelvic-fin rays 8 in holotype and 7–9 in paratypes, third pelvic ray always longest. First, second and third ray slightly thicker than all other pelvic rays. Tip of longest pelvic-fin ray not reaching anus. Pectoral-fin rays 13 in holotype and 12–14 in paratypes, tip of longest pectoral-fin ray does not reach insertion of pelvic fin.

Dentition. Upper jaw with a single row of 12 bicuspid, acute teeth in holotype and 10–16 in paratypes. Upper jaw teeth limited to the premaxilla.

Coloration in alcohol. Ground coloration pale yellow, with few scattered dark melanophores in holotype and paratypes ( Fig. 3 a). Melanophore concentration higher on the dorsal region. Melanophores located mainly on borders of scales, numerous on upper lip, fewer on lower lip. Region around nostrils unpigmented. A thin line of melanophores extending middorsally from tip of snout to interorbital area. Another thin horizontal line of melanophores between tip of snout and eye. Operculum ventrally unpigmented and dorsally slightly pigmented, similar to infraorbitals. Dorsal surface of head strongly pigmented at nape. Ventral surface of head ranging from unpigmented to having scattered, small, dark melanophores. Body covered with 9–12 vertical, dark bars largely under lateral line and 12–15 small, dark blotches along dorsum. Usually wide bars in the predorsal region not ventrally connected. Lateral flank bars in caudal region ventrally connected with each other. Small saddle blotches on dorsum may be faintly connected with flank bars. Caudal peduncle with a large blotch, extending onto caudal fin. Dorsal fin coloration ranging from unpigmented to 1–4 small spots on the first rays. Some young specimens with completely hyaline fins. Adipose fin without coloration. Caudal fin with narrow dark band in each lobe a basally situated, both bands are at the same level, but are not connected to each other. First two rays of anal fin coloured in center with a small spot. Pelvic fin with a dark band in the center, well visible on first three rays. Pectoral fin almost without coloration. Anterior region of the pectoralfin base with a small mark.

holotype holotype + paratypes MRAC 87-24-P-87 Measurements min max mean SD n Total length (mm) 43.5 31.5 48.3 48.3 31 Standard length (SL) (mm) 29.1 25.0 40.7 40.7 31 In percents of standard length

Head length 27.2 25.4 28.3 27.1 0.7 26.7 31 Dorsal-fin length 23.9 18.9 25.7 24.3 1.3 22.6 31 Length of dorsal-fin base 13.5 12.2 14.7 13.2 0.6 12.7 31 Length of anal-fin base 13.3 12.2 13.9 13.1 0.4 11.6 31 Length of adipose-fin base 2.1 1.5 3.1 2.2 0.4 1.8 31 Pelvic-fin length 20.6 19.0 22.0 20.6 0.7 18.8 31 Pectoral-fin length 18.3 15.2 20.5 19.0 1.2 17.9 31 Body depth 18.6 17.0 19.4 17.9 0.6 16.9 31 Body width 10.0 9.6 11.1 10.4 0.3 10.3 31 Caudal peduncle length 13.6 11.3 15.2 13.1 0.8 13.7 31 Preanal distance 72.9 68.7 72.9 70.7 1.1 72.5 31 Prepelvic distance 46.6 42.5 46.6 44.5 0.9 46.1 31 Distance of anus to base of anal fin 3.3 2.2 3.8 2.8 0.4 3.1 31 Dorsal-adipose-distance 25.9 23.0 26.2 24.2 0.8 26.2 31 In percents of head length

Interorbital width 28.9 25.5 29.5 27.9 0.9 23.3 31 Eye diameter 33.1 29.9 34.6 32.6 1.1 28.6 31 Internostril distance 20.3 16.5 20.3 18.2 1.0 16.2 31 Minimal distance between nostril - eye 4.3 4.3 6.9 5.8 0.6 4.5 31 Snout length 26.4 25.1 29.7 27.0 0.9 29.7 31 Upper jaw length 20.6 17.7 23.3 21.4 1.2 16.1 31 In percents of head width

Lower jaw width 36.6 31.7 40.9 36.4 1.9 36.1 31 In percents of body width

Head width 124.7 111.5 128.7 121.9 4.1 121.9 31 Width of pelvic-fin base 63.6 40.9 63.6 52.6 5.9 52.6 31 In percents of body depth

Caudal peduncle depth 63.7 55.9 64.5 63.3 1.9 63.3 31 Body depth at anal-fin end 68.8 57.2 71.1 72.4 3.3 72.4 31 Coloration in life. Field observations show that the species is an overall transparent fish, with a thin reddish band above the clearly visible backbone.

Distribution. Almost all samples of Nannocharax zebra were collected in the Cameroonian portion of the Cross basin, i.e., riffles in the outlet of the Badi River into the Cross River and in the Cross River directly at Mamfé 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 Odieke, Nigeria.

Etymology. The species name zebra is an allusion to the striped pattern of preserved specimens. A noun in apposition.

Ecological notes. Type specimens were collected inshore in areas of relatively calm water among fine twigs of a fallen tree. These twigs were not reaching soil, but remained attached to the crown of the fallen tree and reaching into the free water column. At the peak of the dry season (February), water level is very low in the Cross River at Mamfé and visibility is high resulting in clear water. Specimens sometimes rested on the fine twigs, but mostly were seen moving or hovering in the free water column in a water depth of approx. 50–100 cm (between the twigs), well above the bottom which consisted of leaflitter, sand and fine detritus.

Remarks on special specimen. The single specimen MRAC 87-24-P-87 from Sombreiro River in Nigeria ( Fig. 4 , Table 3) is similar but slightly different from the type series of N. zebra . Unfortunately, this is the only specimen. It is considered conspecific with N. zebra , but not included in the type series.

Figures

FIGURE 3. Holotype of Nannocharax zebra (ZSM 35730), 29.1 mm SL, Cameroon, Cross River at Mamfé, a. Photograph of holotype showing preserved coloration in alcohol, b. Illustration of holotype, drawing by R. Kühbandner.

FIGURE 4. Nannocharax zebra, MRAC 87 - 24 - P- 87, 40.7 mm SL, Nigeria, Sombreiro River at Odieke, showing preserved coloration in alcohol.