Orthochromis gecki, Schedel & Vreven & Manda & Abwe & Manda & Schliewen, 2018

Schedel, Frederic Dieter Benedikt, Vreven, Emmanuel J. W. M. N., Manda, Bauchet Katemo, Abwe, Emmanuel, Manda, Auguste Chocha & Schliewen, Ulrich Kurt, 2018, Description of five new rheophilic Orthochromis species (Teleostei: Cichlidae) from the Upper Congo drainage in Zambia and the Democratic Republic of the Congo, Zootaxa 4461 (3), pp. 301-349 : 323-328

Orthochromis gecki sp. nov.

Orthochromis sp. “Lubudi”

Holotype. MRAC 2012-031 -P-2097 (73.8 mm SL), Democratic Republic of Congo, Lubudi River downstream of Kendo Rapids, near Tshifuntshi Village (-10.5635/24.6354).

Paratype. MRAC 2012-031 -P- 2098-2116 (19, 52.1–77.7 mm SL), collected with holotype .— ZSM 46851 (5, ex MRAC uncat., 46.3–62.9 mm SL), Democratic Republic of Congo, Lubudi River at Kendo Rapids, near Tshifuntshi Village (-10.5668/24.6373). — MRAC 2012-031 -P- 2117-2126 (10, 45.9–69.8 mm SL), Democratic Republic of Congo, Lubudi River at Kendo Rapids, near Tshifuntshi Village (-10.5670/24.6374). – ZSM 46852 (1, ex MRAC uncat., 67.1 mm SL), collected with holotype .

Differential diagnosis. Orthochromis gecki can be readily distinguished from all all species currently placed in Orthochromis (sensu de Vos & Seegers 1998) except O. torrenticola (which has eggspot-like maculae) by presence of eggspots on anal fin. It is further distinguished from O. kasuluensis by having fewer anal-fin rays (8–9 vs. 10); from O. malagaraziensis by having more scales between upper lateral line and dorsal-fin origin (5–8 vs. 3– 4); from O. mazimeroensis by having more horizontal line scales (29–31 vs. 26–28); from O. rubrolabialis , O. rugufuensis and O. uvinzae by having fewer anal-fin spines (16–17 vs. 18–20) and in position of pterygiophore supporting last dorsal-fin spine (vertebral count: 15–16 vs. 17–19). It is furthermore distinguished from O. uvinzae by having fewer abdominal vertebrae (13–14 vs. 15–16) and by position of pterygiophore supporting last anal-fin spine (vertebral count: 14–15 vs. 16–17). O. gecki is distinguished from O. stormsi by having more horizontal line scales (29–31 vs. 26–28) and fewer total gill rakers (9–12 vs. 13–15); from O. polyacanthus by having fewer dorsal-fin spines (16–17 vs. 18–20), more dorsal-fin rays (10–12 vs. 8–9) and it is distinguished by position of pterygiophore supporting last dorsal-fin spine (vertebral count: 15–16 vs. 17–18); from O. torrenticola by having fewer anal-fin spines (3 vs. 4). Meristic values of O. gecki overlap with those of O. luongoensis , O. kalungwishiensis , and O. machadoi but is distinguished by narrower interorbital width (9.62–12.86 vs. 13.18-21.27 % HL). It is distinguished from S. neodon by having more circumpeduncular scales (16 vs. 12); from H. snoeksi by having more anal-fin rays (8–9 vs. 5–6); from H. bakongo by more horizontal line scales (29–31 vs. 26–28), more dorsal-fin spines (16–17 vs. 15–15) and by position of pterygiophore supporting last dorsal-fin spine (vertebral count: 15–16 vs. 13–14); from H. moeruensis by having more horizontal line scales (29–31 vs. 27–28) and more scales in upper lateral line (21–25 vs. 19–20). Meristic values of O. gecki overlap with those of H. vanheusdeni but is distinguished by having a smaller interorbital width (9.62–12.86 vs. 14.20–20.30 % HL). It is distinguished from herein newly described species O. kimpala by having fewer series of scales on cheek (0–2 vs. 3–4). Meristic values of O. gecki overlap with those of O. mporokoso , O. katumbii , and O. indermauri but is distinguished by having smaller interorbital width (9.6–12.9 vs. 13.0–21.7 % HL).

Description. Morphometric measurements and meristic characters are based on 36 type specimens. Values and their ranges are presented in Table 5. For general appearance see figure 6. Maximum length of wild caught specimens 77.7 mm SL. Rather slender and elongated species with maximum body depth (20.2–27.4 % SL) slightly before or at level of first dorsal-fin spine, decreasing rather gradually towards caudal peduncle. Caudal peduncle moderately elongated and deep (ratio of caudal peduncle length to depth: 1.5–2.0). Head length about one third of standard length. Dorsal-head profile moderately curved, from anterior eye region to dorsal-fin origin only slightly curved. No prominent nuchal gibbosity present. Eye diameter larger than interorbital width. Jaws isognathous. Posterior tip of maxilla almost reaching to slightly beyond anterior orbit margin. Lips well developed. Two separate lateral lines.

Squamation. Flank above and below lateral lines covered with comparatively large ctenoid scales. Anterior dorsal and ventral flank covered by cycloid scales. Margin of belly with deeply embedded minute to small sized scales; central belly region scaleless. Chest completely scaleless, except for deeply embedded cycloid scales ventro-anteriorly of pectoral fin. Chest to flank transition relatively abrupt with small, embedded cycloid scales. Snout scaleless. Interorbital region scaleless or with minute, deeply embedded cycloid scales. Nape region covered with minute to small, embedded cycloid scales becoming slightly larger towards occipital region. Occipital region with small to medium sized cycloid scales. Cheek covered with small, partly deeply embedded cycloid scales sometimes almost appearing scaleless; 0-2 scale rows on cheek. Cycloid scales on operculum of variable size (small to medium) and variable shape (ovoid to circular); opercular blotch only on anterior margin covered with medium sized scales, main area of opercular blotch scaleless. 1–3 scales in column from edge of postero-dorsal angle of operculum to anterior edge of operculum.

Upper lateral line scales 21–25 and lower lateral line 8–12. Horizontal line scales 29–31. Caudal fin with 0–1 pored scale. Upper and lower lateral lines separated by two scales. 5–8 scales between upper lateral line and dorsalfin origin. Anterior part of caudal fin covered with 2–3 columns of small cycloid scales; with median scales being slightly larger; scaled area of caudal fin extended posteriorly, especially at upper and lower end, with minute, interradial scales (approximately up to one half of caudal fin). Sixteen scales around caudal peduncle.

Jaws and dentition. Anterior teeth of outer row of upper and lower jaw bicuspid to subequally bicuspid, large and closely set; towards corner of mouth, teeth smaller and more widely set and becoming unicuspid (rarely tricuspid or subequally bicuspid teeth present in posterior upper jaw). Individual bicuspid teeth without or minimally expanded brownish crown, cusps (tips roundish) uncompressed and moderately narrowly set, neck moderately stout. Outer row of upper jaw with 33–49 teeth and outer row of lower jaw with 26–42 teeth (specimens: 46.3–77.7 mm SL); larger specimens generally with more teeth. Upper and lower jaw with 2–4 inner tooth rows with small tricuspid teeth (rarely 5 rows in upper jaw and 1 or 5 in lower jaw); larger specimens generally with more inner tooth rows. Lower pharyngeal bone ( Fig. 6 ) of single dissected paratype (MRAC 2012- 031-P- 2098-2116, 69.1 mm SL) about 1.1 times wider than long with anterior keel about 0.6 times length of dentigerous area. Dentigerous area of lower pharyngeal bone about 1.4 times wider than long, with 10+9 teeth along posterior margin and 6 teeth along midline. Anterior pharyngeal teeth (towards keel) bevelled to pronounced and slender; those of posterior row larger than anterior ones, bevelled (minor cusp not well developed). Largest teeth medially in posterior tooth row. Teeth along midline slightly larger than more lateral ones.

Gill rakers. Total gill raker count 9–12, with 1–2 epibranchial, one angle, and 7–9 ceratobranchial gill rakers. Anteriormost ceratobranchial gill rakers smallest, increasing in size towards cartilaginous plug (angle). Anterior gill rakers on ceratobranchial unifid, towards cartilaginous plug sometimes bifid or trifid. Raker on cartilaginous plug largest in size and in most cases trifid, sometimes bifid. Epibranchial gill rakers then decreasing in size.

Fins. Dorsal fin with 16–17 spines and with 10–12 rays. First dorsal-fin spine always shortest. Dorsal-fin base length between 52.1–61.0 % SL. Posterior tip of dorsal-fin rays reaching slightly beyond caudal fin base; posterior tip of anal fin reaching slightly before or at caudal-fin base. Caudal fin outline subtruncate and composed of 27–29 rays (16 principal caudal-fin rays and 11–13 procurrent caudal-fin rays). Anal fin with 3 spines (3rd spine longest) and 8–9 rays. Anal-fin base length between 15.6–20.7 % SL. Pectoral fin with 15–16 rays. Pectoral-fin length between 19.6–25.0 % SL; longest pectoral ray not reaching level of anus; first upper and lower pectoral-fin rays very short to short. Pelvic fin with 1 st spine thickly covered with skin and 5 rays. Pelvic-fin base at level or slightly anterior of pectoral-fin base. Pelvic fin ending at same level as pectoral fin; longest pelvic-fin ray not reaching anus (ending approximately 2-3 flank scale widths before).

Vertebrae and caudal fin skeleton. 29–31 total vertebrae (excluding urostyle element), with 13–14 abdominal and 16–18 caudal vertebrae. Pterygiophore supporting last dorsal-fin spine inserted between neural spines of 15th and 16th or 16th and 17th vertebra (counted from anterior to posterior). Pterygiophore supporting last anal-fin spine is inserted between haemal spines of 15th and 16th vertebra or between rips of 14th and haemal spine of 15th vertebra. Single predorsal bone (=supraneural) present. Hypurals 1 and 2 in most types fused into either single, seamless unit or separated by clearly distinct seam. Hypurals 3 and 4 always fused into single seamless unit, except for one paratype which has clearly separated hypurals.

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Colouration in life (based on field photographs of adult specimens). Body ground colouration brownish to greyish; dorsum, flanks and caudal peduncle greyish, beneath lower lateral line becoming yellowish; belly yellow; chest anteriorly whitish and remaining area yellow. Dark grey interrupted midlateral band from eye (anteriorly extended midlateral band) to just behind caudal-fin base ending in well pigmented vertically elongated blotch. Midlateral band crossed by 7–9 greyish vertical bars; at level of upper lateral line they sometimes fuse with each other forming dorso-lateral band sometimes interrupted and ending at posterior end of dorsal fin. On ventral flank at level of pectoral fin vertical bars sometimes fuse to ventro-lateral band (less intensive then previous mentioned ones) that ends well before level of anus. Iris dorsally yellow remaining greyish. Dorsal head surface, ethmoidal area, preorbital area greyish; cheek greyish near eyes, yellowish below and with vertical stripe-like pattern centrally (less distinct than other stripes of face mask). Preoperculum light greyish-yellow; operculum greyish, black opercular spot outlined with yellow. Branchiostegal membrane brownish to orange. Dark grey lachrymal stripe ending slightly anterior of caudal end upper lip. Greyish nostril stripe caudally fused with lachrymal stripe (beneath eye); interorbital stripe greyish. No clearly defined supraorbital stripe or nape band but recognizable to some extent by darker (grey) colouration than remaining dorsal head surface. Upper lip and lower lip yelloworange; upper and lower margin of upper lip greyish. Dorsal-fin membrane brownish (especially spinous part) to yellowish (soft rayed part); margin orange; brownish to dark greyish maculae from about posterior half of spiny part to end soft-rayed part arranged in several almost vertical columns. Anal-fin membrane transparent proximally becoming yellowish distally (soft rayed part), margin of spiny and soft-rayed part black becoming yellow to brownish towards posterior tip; 3–6 orange eggspots (large orange centre surrounded by yellow concentring ring and outlined by more or less ill-defined transparent margin) on anal fin in both sexes. Eggspots arranged into 1–2 rows, first eggspot located centrally on fin just behind last anal spine. Caudal fin yellowish, orangey distally, margin outlined in grey-black; caudal with brownish maculae arranged into 3–4 vertical columns. Pectoral fin transparent, rays greyish. Pelvic fin deep black (especially skin around spine) except for small yellow central portion of rayed area.

Juvenile colouration in live. (based on wild caught juveniles of approximately 25 mm SL; Fig. 9 ). Ground colouration beige, belly whitish. Patterns and head mask as described for adults but less prominent. Brown to greyish vertical bars on flank appear wider than in adults, dorso-lateral band and ventro-lateral band not visible. Last vertical bar on caudal fin base roundish blotch extending onto caudal fin (not a vertical bar as in adults). Dorsal fin brownish with several hyaline patches, margin not orange. Anal fin light brownish-orange; no eggspots on anal fin present. Caudal fin brownish-orange, no maculae present. Pectoral fin hyaline. Pelvic fin white to yellowish.

Colouration in alcohol. Colouration and melanin patterns similar to live specimens, due the preservation procedure of specimens, i.e., first formalin fixation, transfer to 75 % EtOH etc., specimens tend to lose original colouration (especially melanin patterns more intense than in live specimens). Overall body ground colouration brownish; dorsum and flank brownish becoming brighter ventrally. Chest and belly light brown to beige. Branchiostegal membrane dark greyish. Dorsal head surface brownish; ethmoidal area greyish brown. Upper and lower lip beige; upper and lower margin of upper lip greyish brown. Cheek light brown to brownish; cheek stripe dark brown. Operculum dark brown becoming somewhat darker ventrally; with opercular spot as described above. Head mask dark grey. Midlateral band, vertical bars, dorso-lateral band and ventro-lateral band dark brown. Dorsal fin greyish brown becoming greyish beige caudally, margin blackish with very fine black seam; maculae on spiny and soft-rayed part dark grey. Anal fin beige with blackish distal margin and dark grey at posterior margin; eggspots on anal fin faded and not visible in preserved specimens. Caudal fin beige to light greyish with dark greyish margin; maculae dark grey. Pectoral fin beige to light grey. Pelvic fin deep black except small central portion of rayed part greyish.

Distribution and biology. Orthochromis gecki is known from the Lubudi River a left-hand tributary of the Lualaba River in the Katanga region, Democratic Republic of the Congo ( Fig. 1 ). It was also found to be present in the Mukuleshi River. At the type locality the Lubudi River has a rocky bottom with patches of gravel and sand, and is about 15 meters wide and about 50 cm deep; upstream the river is much deeper with 3 meters or more ( Fig. 9 ).

O. gecki seems to be a maternal mouthbrooder. One of the female paratypes (MRAC 2012-031-P- 2117-2126; 57.0 mm SL), was found mouthbrooding when preserved and carried around 12 comparatively large eggs. Fixed eggs are brownish and oval and ca. 3.8 mm long and 2.5 mm wide.

Etymology. The species is named in honour of Mr. Jakob Geck who is a passionate, German fish naturalist, thanking him for his dedicated volunteer work and untiring support for the ichthyology section of the ZSM. His great experience in keeping rheophilic cichlids contributed to the knowledge of behaviour and ecology of many cichlid taxa, including O. katumbii and O. indermauri .

Figures

FIGURE 1. Map of south-eastern DRC and Northern Zambia, with indications of the type localities of the known Orthochromis species of the Upper Congo drainage system and new Orthochromis species. Star = type locality, circle = either paratype locality or sample locality of comparative specimens. Species indicated by colour: O. mporokoso sp. nov. (light blue); O. katumbii sp. nov. (purple); O. kimpala sp. nov. (orange); O. gecki sp. nov. (deep orange); O. indermauri sp. nov. (deep blue); O. kalungwishiensis (dark red); O. luongoensis (green). O polyacanthus (brown) and O. torrenticola (yellow). Major citys are depicted in black. Map is based on shapefiles obtained from DIVA-GIS (http://www.diva-gis.org/Data).

FIGURE 6. Orthochromis gecki sp. nov. A. probably the holotype, alive B. Holotype (MRAC 2012-031-P-2097), 73.8 mm SL; Democratic Republic of the Congo, Lubudi River C. radiograph of holotype D. lower pharyngeal bone (specimen with 69.1 mm SL; MRAC 2012-031-P-2098-2116) E. Overview of arrangement and morphology of oral jaw teeth (specimen with 75.0 mm SL; MRAC 2012-031-P-2098-2116).

FIGURE 9. Live Pictures of juveniles. A. captive raised F1 juvenile of Orthochromis katumbii about 25 mm SL (Photo J. Geck). B. wild caught juvenile of Orthochromis gecki C. captive raised F1 juvenile of Orthochromis indermauri.