Chiloglanis igamba, Friel, John P. & Vigliotta, Thomas R., 2011

Friel, John P. & Vigliotta, Thomas R., 2011, Three new species of African suckermouth catfishes, genus Chiloglanis (Siluriformes: Mochokidae), from the lower Malagarasi and Luiche rivers of western Tanzania, Zootaxa 3063, pp. 1-21 : 4-8

publication ID	https://doi.org/ 10.5281/zenodo.202193
DOI	https://doi.org/10.5281/zenodo.5632905
persistent identifier	https://treatment.plazi.org/id/9A2AC44D-FFAA-FFAF-FF21-FF02FEBAA4EE
treatment provided by	Plazi
scientific name	Chiloglanis igamba
status	sp. nov.

Treatment

Chiloglanis igamba View in CoL sp. nov.

( Figs. 1 View FIGURE 1 A & 3; Table 1 View TABLE 1 )

Chiloglanis aff. lufirae View in CoL — De Vos et al. 2001: 131. Chiloglanis sp. “ igamba ” — Vigliotta 2008: 125.

Holotype. CU 90576, 1 male ALC, 64.6 mm SL; Tanzania, Kigoma Region, Malagarasi River at Lower Igamba Falls, 5.1802° S, 30.503° E; J.P. Friel & S. Loader, 9 October 2004.

Paratypes. AMNH 251401, 40 ALC, 27.2–61.8 mm SL; Tanzania, Kigoma Region, Malagarasi River at Lower Igamba Falls, 5.1800100° S, 30.0508300° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 5 August 2009. — CU 94005, 36 males ALC (8 measured for Table 1 View TABLE 1 ), 27.6–63.5 mm SL, 13 females ALC (6 measured for Table 1 View TABLE 1 ), 29.3– 3.6 mm SL, 2 undetermined gender C&S; same collection data as holotype. — CU 95220, 41 ALC, 26.0– 61.7 mm SL; same collection data as AMNH 251401. — MRAC 2010-006- P- 1-5, 5 ALC, 30.8–56.8 mm SL; same collection data as AMNH 251401. — SAIAB 87163, 5 ALC, 30.9–56.2 mm SL; same collection data as AMNH 251401.

Non-type specimens. AMNH 251402, 10 ALC, 34.4–54.5 mm SL; Tanzania, Kigoma Region, Malagarasi River between Upper Igamba Fall and High Fall, 5.1785800° S, 30.0730600° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 6 August 2009. — AMNH 251403, 4 ALC, 33.7–60.4 mm SL; Tanzania, Kigoma Region, Malagarasi River at rapids ~ 8 km downriver of Igamba Falls, 5.1799300° S, 29.9803500° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 7 August 2009. — AMNH 251404, 4 ALC, 28.0– 36.5 mm SL; Tanzania, Kigoma Region, Malagarasi River upriver ~ 12 km E of Uvinza, near village of Kanzibwe, 5.1398600° S, 30.4893200° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 10 August 2009. — AMNH 251405, 22 ALC, 24.3–47.0 mm SL; Tanzania, Kigoma Region, Malagarasi River downriver ~ 4 km W from Uvinza; near village of Nkwasa, 5.0979300° S, 30.3544900° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 11 August 2009. — AMNH 251406, 3 ALC, 32.3–47.6 mm SL; Tanzania, Kigoma Region, Malagarasi River near fork in road to village of Ngutu, 5.1156300° S, 30.2966800° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 12 August 2009. — AMNH 251407, 34 ALC, 27.6–56.0 mm SL; Tanzania, Kigoma Region, Malagarasi River within gorge, 5.2289500° S, 30.2240300° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 17 August 2009. — AMNH 251408, 3 ALC, 24.8–34.2 mm SL; Tanzania, Kigoma Region, Malagarasi River within gorge, 5.2028300° S, 30.1697500° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 18 August 2009. — CU 90410, 1 male ALC, 34.5 mm SL; Tanzania, Kigoma Region, small side channel of Malagarasi River at Uvinza, 5.1110000° S, 30.3932000° E; J.P. Friel, G. Kazumbe & S. Loader, 18 September 2004. — CU 90428, 1 male ALC, 31.3 mm SL, 1 female ALC, 37.1 mm SL; same collection data as holotype. — CU 90569, 9 male ALC, 22.1– 3.9 mm SL, 8 female ALC, 24.1–30.2 mm SL; same collection data as CU 90410. — CU 90572, 1 male ALC, 32.1 mm SL; Tanzania, Kigoma Region, Malagarasi River at Igamba Falls, 5.1802000° S, 30.0505000° E; J.P. Friel & S. Loader, 17 September 2004. — CU 95221, 10 ALC, 28.9–36.1 mm SL; same collection data as AMNH 251402. — CU 95222, 4 ALC, 33.7–58.1 mm SL; same collection data as AMNH 251403. — CU 95223, 3 ALC, 29.0– 51.8 mm SL; same collection data as AMNH 251404. — CU 95224, 22 ALC, 22.8–47.3 mm SL; same collection data as AMNH 251405. — CU 95225, 4 ALC, 29.5–55.1 mm SL; same collection data as AMNH 251406. — CU 95226, 35 ALC, 25.3–62.7 mm SL; same collection data as AMNH 251407. — CU 95227, 4 ALC, 25.7–36.0 mm SL; same collection data as AMNH 251408. — MRAC P 94068.0002–0006, 1 male ALC, 4 female ALC; Tanzania, Kigoma Region, Malagarasi River at the rapids near Uvinza salt mine, 5° 06' S, 30° 22' E; L. De Vos, 21 October 1994.

Diagnosis. Chiloglanis igamba is a sexually dimorphic species in which the caudal fin of adult males is relatively truncate, but with the middlemost rays moderately elongated ( Figs. 2 View FIGURE 2 & 3 View FIGURE 3 ). Females and juvenile males of this species in contrast exhibit a gently forked caudal fin. Sexual dimorphism of the caudal fin is also apparent in several species of Chiloglanis , including the following from various tributaries flowing into Lake Tanganyika: C. trilobatus , C. kalambo , C. productus and C. asymetricaudalis . However, the particular shape of the caudal fin in C. igamba is unique among all congeners ( Figs. 2 View FIGURE 2 & 3 View FIGURE 3 ; see also Fig. 5 View FIGURE 5 in Ng & Bailey 2006 or Fig. 155 in Seegers 1996).

The most similar sexually dimorphic caudal fins are found in males of C. trilobatus and C. kalambo , where the middle most rays form a third lobe ( Fig. 2 View FIGURE 2 ). The trilobate caudal-fin shape in these species can be distinguished from the shape in C. igamba by the areas between upper, middle and lower lobes, which are notably recessed. In C. igamba these recessed areas are absent and a clearly trilobate shape is not evident. Chiloglanis igamba is further distinguished from C. trilobatus and C. kalambo by a shorter adipose-fin base length (10.3–16.3% SL vs. 16.4– 22.3% SL in C. trilobatus and 16.5–23.4% SL in C. kalambo ); a shorter depth at dorsal fin insertion (14.5–18.4% SL vs. 20.0–24.0% SL in C. trilobatus and 18.2–23.5% SL in C. kalambo ; taken to be equivalent to Seegers (1996) “body depth”); a shorter caudal peduncle depth (8.7–12.6% SL vs. 11.9–14.5% SL in C. trilobatus and 11.3–15.4% SL in C. kalambo ); a longer snout length (20.3–26.2% SL, mean 23.0% SL vs. mean of 19.9% SL in C. trilobatus and mean of 18.4% SL in C. kalambo ); a shorter maxillary barbel (5.0–7.5% SL, mean 6.1% SL vs. mean of 10.6% SL in C. trilobatus and mean of 9.3% SL in C. kalambo ); a wider oral disc (20.4–26.8% SL, mean 24.5% SL vs. mean of 19.0% SL in C. trilobatus and mean of 19.7% SL in C. kalambo ); a wider set of premaxillary tooth plates (15.6–19.8% SL, mean 17.9% SL vs. mean of 14.0% SL in C. trilobatus and mean of 13.7% SL in C. kalambo ); 27–45 primary teeth on each premaxilla (vs. 18–31 in C. trilobatus and 7–21 in C. kalambo ); 6 soft rays in the dorsal fin, rarely 5 (vs. 5 rays in C. trilobatus and C. kalambo ).

Caudal-fin shape in males of C. igamba is also fairly similar to the shape found in males of C. productus . However, in C. productus all caudal-fin rays, especially the middle rays, are elongated and the fin is diamond shaped. ( Fig. 2 View FIGURE 2 ). Chiloglanis igamba is also easily distinguished from C. productus by its pigmentation, which consists of cream-colored splotches on a light brown background. In contrast, the pigmentation of C. productus is medium to dark brown with a pale midlateral stripe along the lateral line. Chiloglanis igamba is further distinguished from C. productus by a shorter pectoral spine (9.9–15.1% SL vs. 15.2–18.5% SL); a shorter pectoral-fin longest ray (15.2– 18.8% SL vs. 19.1–23.9% SL); and a shorter adipose-fin base (10.3–16.3% SL vs. 22.5–26.2% SL).

Finally, in Chiloglanis asymetricaudalis the caudal fin of adult males is forked, but with an elongate upper lobe ( Figs. 2 View FIGURE 2 & 6 View FIGURE 6 ). In addition to caudal fin shape, Chiloglanis igamba is easily distinguished from C. asymetricaudalis by a shorter pectoral spine (9.9–15.1% SL vs. 16.4–19.7% SL); a shorter dorsal spine (8.2–12.7% SL vs. 13.0– 15.7% SL); a shorter anal fin (11.7–15.9% SL vs. 22.6–28.0% SL); a shorter caudal peduncle (15.0–17.7% SL vs. 18.4–20.9% SL); and a markedly different pigment pattern ( Fig. 3 View FIGURE 3 vs. Fig. 6 View FIGURE 6 ).

Description. Dorsal, lateral and ventral views in Figure 3 View FIGURE 3 illustrate body shape, form and position of fins and barbels. Morphometric and meristic data for holotype and 14 syntopic paratypes are summarized in Table 1 View TABLE 1 .

continued next page MERISTICS

Mandibular tooth rows 1 or 2* Mandibular tooth count (total) 8–16* Mandibular tooth count (functional anterior row) 7–8*

Mandibular tooth count (posterior replacement row) 0–8*

Primary premaxillary teeth (total) 57–89; 63* Secondary premaxillary teeth (total) 20–40 Tertiary premaxillary teeth (total) 8–16

Pectoral-fin count I, 8*(11); I, 9(4) Pelvic-fin count i, 6*(15) Dorsal-fin count II, 5 (2); II, 6*(13) Anal-fin count iii, 6(1); iii, 7*(12); iii, 8(2) Caudal-fin count i, 7, 8, i*(15) Pleural rib count (pairs) 7*(11); 8(4) Total vertebral count 33*(15)

Moderately sized Chiloglanis species, maximum standard length <70 mm. Body roughly cylindrical, depressed anteriorly and compressed posteriorly. Predorsal profile convex; postdorsal body sloping gently ventrally. Preanal profile horizontal. Anus and urogenital opening located at vertical though origin of adipose fin. Skin with numerous small unculiferous tubercles, especially towards head and along dorsal midline. Lateral line complete and midlateral along side of body.

Head depressed and broad, snout margin rounded when viewed dorsally. Gill opening restricted to lateral aspect of head from level of base of pectoral spine to level of middle of eye. Gill membranes broadly united to, and attached across isthmus, supported by 5 or 6 branchiostegal rays. Bony elements of skull roof lack any superficial ornamentation. Skin covering skull roof with numerous small, round unculiferous tubercles. Occipital-nuchal shield small, not visible through skin dorsally.

Mouth inferior, lips form ventrally-directed oral disc. Oral disc quite large, nearly as wide as head and covered by numerous papillae. Posterior margin of oral disc with well-developed cleft present at midline. Barbels in three pairs. Maxillary barbel short, thick and unbranched, about as long as diameter of eye; emanating from posterolateral region of oral disc. Mandibular barbels incorporated into lower lip and visible as trifurcate structures in cleared and stained specimens. Medial mandibular barbels on each side of midline; primary and auxiliary barbels visible as three small bumps in lower lip margin. Lateral mandibular barbels just lateral to medial mandibular barbels, somewhat more pronounced; primary and auxiliary barbels visible as three small bumps in lower lip margin; middle of tips presenting as short pointed barbel, one half length of maxillary barbel.

Premaxillae formed as claw-shaped plates supporting 57–89‚“S”-shaped (in lateral view), pointed primary teeth distrubuted in oval patches on ventral surface; 20–40 smaller secondary teeth on posterior surface of premaxillae; 8–16 needle-like teeth inserting above and behind secondary teeth towards roof of mouth and gathered at midline. Number of premaxillary teeth increases with overall body size. Dentary with well-formed tooth cup along anterior margin supporting one or two rows of 7 or 8 robust, “S”-shaped (in lateral view) teeth with pointed tips; when present, posterior row represents replacement teeth. Mandibular teeth bunched at midline ( Fig. 1 View FIGURE 1 A & Fig. 3 View FIGURE 3 ).

Eyes small and ovoid, horizontal axis slightly longer than vertical axis; less than one third of orbital interspace. Orbit without free margin. Anterior nares and posterior nares equidistant. Anterior nares tubular with short, raised rim. Posterior nares with elevated flaps along anterior margin.

Dorsal fin located at anterior third of body. Dorsal fin with spinelet, spine and 5 or 6 rays; fin membrane not adnate with body. Dorsal-fin spine short and straight, between 2 to 3 times as long as diameter of eye; smooth along anterior and posterior margins. Adipose fin short, base up to one sixth of SL, originating near posterior third of body; margin convex and deeply incised posteriorly. Caudal fin sexually dimorphic; shallowly forked in females and trilobate in males (middle rays elongated); count i, 7, 8, i. Procurrent caudal-fin rays symmetrical and extending only slightly anterior to fin base. Anal-fin base located ventral to adipose-fin base; margin convex. Anal-fin count iii, 6–8. Pelvic-fin origin at vertical between bases of adipose and dorsal fin. Pelvic-fin margins convex, tip of appressed fin just reaching anal-fin origin. Pelvic-fin count i, 6. Pectoral fin with slightly curved, short, stout spine; anterior and posterior spine margins smooth. Pectoral fin count I, 8 or 9. Cleithral processes short and obtusely pointed, largely buried in skin. Very small axillary pore present, but may be difficult to see or obscured by cleithral process in some specimens.

In addition to dimorphism in shape of caudal fin, dimorphism in body size is present: largest specimens in all samples examined are males.

Coloration. In 70% ethanol: The general pigmentation of this species is shown in Figure 3 View FIGURE 3 . In dorsal view, specimens appear medium brown, with indistinct lighter bands or rows of spots posterior to head. Most wellformed bands between dorsal and adipose fins and at terminus of adipose fin. Head uniformly light to medium brown.

In lateral view, specimens appear mostly medium brown with lighter abdomen and numerous lighter spots. Above lateral line, small spots in 6 or 7 evenly spaced vertical rows, corresponding to free neuromasts; spots slightly enlarged between bases of dorsal and adipose fin bases and at terminus of adipose fin. Lateral line with tiny lighter spots corresponding to pores. Below lateral line, large light spots at anal fin origin and below terminus of adipose fin.

Ventral surface cream colored with some spots of dark pigment from origin of pelvic fins to end of anal-fin base. Oral disc, all barbels, anus and urogenital opening cream colored.

Dorsal and pectoral spines and rays light brown; base of dorsal and pectoral-fin rays generally darker; fin membranes nearly translucent. Pelvic and anal fins milky-white; base of anal-fin rays darker or cream colored. Adipose fin with medium brown base and translucent milky-white posterodorsal margin. Base of caudal-fin rays dark; wide band of darker pigment along middle of rays separated from dark basal color by cream-colored patch; tips generally cream colored.

Etymology. The specific name refers to the type locality of this species, Igamba Falls on the Malagarasi River. This is the first major series of waterfalls encountered while navigating upriver from Lake Tanganyika, and is a potential site for a hydroelectric dam. Used as a noun in apposition.

Distribution. This species is known from two general localities in the lower Malagarasi River (the type locality at Igamba Falls ( Fig. 2 View FIGURE 2 ) and upriver near Uvinza), and is probably endemic to the basin. This species is most abundant within the Igamba Falls area and associated large rapids, and is much less common in smaller rapids both above and below these falls.

References

Figures

Tables

TABLE 1. Summary of morphometric measurements and meristic counts for Chiloglanis igamba sp. nov. (N = 15; holotype and 14 paratypes). Standard length expressed in mm. All other measurements expressed as % SL. Meristic data for holotype is identified by an asterisk, and the number of specimens with a particular value for fin rays, ribs and vertebrae is shown in parentheses.

MORPHOMETRICS	Holotype	Range	Mean±%SD
Standard length (mm)	64.6	30.0–64.6
Head length	36.7	31.3–37.5	35.3±1.79
Head depth (maximum)	17.8	13.8–17.8	16.1±1.20
Body depth at anus	13.9	12.2–14.7	13.3±0.71
Occipital shield width (minimum)	4.0	2.8–4.9	3.7±0.59
Prepectoral length	33.9	27.3–34.4	31.6±2.01
Predorsal length	42.3	39.7–44.5	41.8±1.57
Prepelvic length	58.7	55.8–60.3	57.8±1.28
Preanal length	70.3	67.8–72.6	70.1±1.64
Eye diameter (horizontal)	3.9	3.9–5.5	4.9±0.46
Orbital interspace	10.1	7.9–11.4	9.3±0.92
Snout length	25.4	20.3–26.2	23.0±2.02
Premaxillary tooth-patch width	16.6	15.6–19.8	17.9±1.18
Premaxillary tooth-patch length	4.2	3.3–4.4	3.8±0.35
Mandibular tooth row width	3.3	1.8–4.4	2.7±0.67
Anterior nares interspace	5.1	4.4–5.7	5.1±0.40
Posterior nares interspace	5.3	4.5–5.5	5.0±0.29