Amphilius ruziziensis Thomson & Page

Thomson, Alfred W., Page, Lawrence M. & Hilber, Samantha A., 2015, Revision of the Amphilius jacksonii complex (Siluriformes: Amphiliidae), with the descriptions of five new species, Zootaxa 3986 (1), pp. 61-87 : 68-70

Amphilius ruziziensis Thomson & Page , new species

( Fig. 4 , Table 3 )

Amphilius platychir (non Günther).— Marlier, 1953: 194, distribution in Ruzizi drainage; Distribution mapped.

Holotype. MRAC 93294, Rwanda, Lufiro River, upper reaches of Matchuza, Ruzizi River drainage, ca. 2°44'00”S, 29°02'99"E (82.8 mm SL)

Paratypes. CU 97332, ex. MRAC 93300, same data as holotype (1: 47.7); MRAC 91529–531, Democratic Republic of the Congo, Kiliba River, ca. 3°14'30”S, 29°09'36”E (3: 31.2–64.9); MRAC 93295–297, same data as holotype, (3: 41.3–45.3); MRAC 93126–128, Burundi, Nyakagunda River, ca. 2°47'S, 29°04'E (3: 37.5–66.5); MRAC 93129–130, Burundi, Nyamagana River, ca. 2°55'S, 29°08'E (2: 116.1–120.6); MRAC 93131, Burundi, Lua River, ca. 2°46'S, 29°02'E (1: 79.5); SAIAB 187262, ex. MRAC 93298, same data as holotype (1:64.2); UF 184236, ex. MRAC 93299, same data as holotype (69.8).

Non-types. Mutimbuzi River drainage: MRAC 91330–389, Burundi, Murago River, ca. 3°17'S, 29°23'E (59: 29.2–71.4); MRAC 93076–096, Burundi, Musazi River [=Muzazi River], ca. 3°17'S, 29°25'E (20: 33.1–91.0); MRAC 126266–267, Burundi, Murago River, ca. 3°17'S, 29°23'E (7: 41.3–82.8). Ruzizi River drainage: MRAC 91034.0153–0159, Burundi, Nyamagana River near town of Mabayi, ca. 2°42'S, 29°15'E (7: 47.7–79.9); MRAC 91390, Burundi, Nyakagunda River, Bugarama, ca. 2°47'S, 29°04'E (1: 25.6); MRAC 93051–054, Democratic Republic of the Congo, Muniowe River, Luvungi, ca. 2°56'S, 28°57'E (4: 43.9–95.2); MRAC 93055–075, Democratic Republic of the Congo, Luvubu River, ca. 2°52'S, 29°02'E (20: 27.3–108.5); MRAC 93121–125, Burundi, Nyamagana River, ca. 2°55'S, 29°08'E (5: 44.1–97.6), MRAC 96031.1571–1576, Burundi, Nyamagana River, 3 km after Mabayi, center Kivogero, ca. 2°42'56”S, 29°14'40”E (5: 46.2–88.0); MRAC 96031.1590–1595, Ikibenga River, 26 km on Cibitoke-Mabayi road, ca. 2°43'03”S, 29°10'05”E (6: 50.5–69.3). Unknown drainage: MRAC 91392–395, Burundi, Kikoma River, ca. 3°20'S, 29°18'E (4: 45.3–86.6).

Diagnosis. Diagnostic characters are summarized in Table 2 . A. ruziziensis is diagnosed from A. pedunculus , A. frieli , and A. crassus by its more slender caudal peduncle (caudal peduncle depth 8.6–9.5% SL vs. 9.7–12.3% SL) and from A. jacksonii , A. pedunculus , A. crassus , and A. lujani by its narrower interorbital width (23.4–25.1% HL vs. 26.7–35.8% HL). It is further diagnosed from A. frieli , A. crassus , and A. lujani by its more slender body (body depth at anus 11.1–12.9% SL vs. 13.5–17.4% SL). A. ruziziensis is further diagnosed from A. frieli by having fewer branchiostegal rays (6–7 vs. 8–9), fewer total gill rakers on the first gill arch (6–8, rarely 5 or 9 vs. 10–11, rarely 9 or 12), and a longer caudal peduncle (caudal peduncle length 18.7–20.3% SL vs. 14.4–16.4% SL). It is further diagnosed from A. crassus by a longer caudal peduncle (caudal peduncle length 18.7–20.3% SL vs. 13.3– 15.5% SL) and shorter dorsal-fin insertion to adipose-fin insertion length (38.2–41.5% SL vs. 42.2–44.6% SL). It is further diagnosed from A. jacksonii by its deeper caudal peduncle (caudal peduncle depth 8.6–9.5% SL vs. 4.8– 7.9% SL).

Description. Morphometric data are in Table 3 . Body elongate, ventral profile flattened ventrally to anal-fin base, then tapered dorsally to end of caudal peduncle. Dorsal profile rising gently from tip of snout to dorsal-fin origin, then nearly horizontal to end of caudal peduncle. Greatest body depth at dorsal-fin origin. Caudal peduncle laterally compressed, with crenellated epidermal fold. Anus and urogenital openings located at midpoint of adpressed pelvic fin, much closer to pelvic-fin insertion than to origin of anal fin. Skin smooth. Lateral line complete, extending from dorsal edge of opercular cavity to caudal-fin base.

Head and anterior part of body depressed and broad. Head wedge-shaped in lateral view. Snout broad, blunt to rounder when viewed from above. Head becoming wider from tip of snout to pectoral-fin base. Branchiostegal membranes moderately to broadly joined at isthmus forming a U -shaped connection.

Mouth broad, gently curved, subterminal. Lips moderately fleshy, slightly papillate. Rictal lobe large and slightly papillate. Anterior portion of premaxillary tooth band exposed with mouth closed. Premaxillary tooth patches joined, forming crescent shaped band. Premaxillary and dentary teeth short, conical. Dentary tooth patches forming U -shaped band, separated medially.

Three pairs of simple, tapered circumoral barbels. Maxillary barbel large, fleshy and flattened with pointed tip; barbel extending posterolaterally from corner of mouth, not reaching pectoral-fin base. Outer mandibular barbel thin with pointed tip, origin at posterior corner of lower jaw, extending to just short of origin of pectoral-fin. Inner mandibular barbel originates anterolaterally of inner mandibular barbel, extending to about two-thirds of distance to edge of branchiostegal membrane. Branchiostegal membrane with 6 (7), or 7 (8) rays. Gill rakers on first epibranchial 2 (15) or 3 (1); rakers on first ceratobranchial 3 (1), 4 (8), 5(2), 6 (4), or 7 (1); total gill rakers on first arch 5 (1), 6 (8), 7 (1), 8 (5), or 9 (1).

Eye small, positioned dorsolaterally approximately midway between tip of snout and posterior margin of operculum. Horizontal diameter of eye slightly wider than vertical diameter. Eye without free orbit; covered with skin confluent with dorsal surface of head. Anterior and posterior nares with prominent tubular rims; nares separate but relatively close to each other. Posterior nare located about midway between eye and tip of snout.

Dorsal-fin origin at point over or just posterior to tip of pectoral fin. Dorsal fin with i,6 (16) rays, and fin margin straight. Pectoral fin with i,8 (2), or i,9 (14) rays; unbranched ray greatly thickened. Pectoral fin with four or five innermost rays progressively shorter making posterior fin margin rounded. Origin of pelvic fin posterior of dorsal-fin insertion. Pelvic fin with i,5 (16) rays with first ray unbranched and greatly thickened. Pelvic fin with straight posterior margin.

Adipose-fin base longer than anal-fin base, origin anterior to origin of anal-fin base, fin extending past anal-fin insertion. Margin strongly convex with sharply rounded edge, deeply incised posteriorly. Caudal fin moderately forked with tips of lobes rounded; fin with i,5,6,i (15) principal rays. Anal fin with short base, origin posterior to origin of adipose-fin base, with ii,5 (3), ii,6 (2), iii5 (1), iii,6 (7), or iii,7 (3) rays. Anal-fin margin almost straight.

Coloration. Body variably mottled with dark saddles. First saddle posterior of head, second saddle at dorsal fin, third saddle between dorsal and adipose fins, fourth saddle under anterior part of adipose fin, and fifth saddle on caudal peduncle. All saddle connected laterally by broad stripe. Venter light brown with fourth saddle meeting that of opposite side Dorsal, and anal fins brown with dark medial band (band on anal fin often indistinct on small specimens). Adipose fin dark brown, cream-colored anteriorly, posteriorly and on distal edge. Pectoral and pelvic fins positioned horizontally with upper surfaces brown with cream-colored distal edge. Lower surfaces light yellow. Caudal fin cream-colored with medial dark band.

Distribution. Ruzizi River drainage, eastern Rwanda and Burundi; western Democratic Republic of the Congo; northeastern tributaries of Lake Tanganyika in Burundi ( Fig. 3 ).

Etymology. Named for the Ruzizi River drainage in eastern Rwanda and Burundi, where type specimens of this species were collected and the species is primarily distributed.

Figures

FIGURE 3. Distributions of Amphilius jacksonii (dots) and A. ruziziensis (triangles).

FIGURE 4. Amphilius ruziziensis, MRAC 93294 82.8 mm SL, holotype; lateral, dorsal and ventral views.

Tables

TABLE 3. Morphometric data for Amphilius ruziziensis. Range and mean include the holotype.

	Holotype	Range (n=7)	Mean±SD
%SL
Head length	21.6	21.6–26.9	24.5±2.1
Head width	17.9	17.9–20.3	19.2±1.1
Head height	11.5	11.5–13.7	12.5±0.8
Body depth	14.0	12.9–14.2	13.6±0.5
Body depth at anus	11.1	11.1–12.9	12.1±0.8
Predorsal length	37.8	35.2–40.1	37.6±1.7
Prepectoral length	16.6	15.1–22.4	18.9±2.7
Preanal length	69.2	68.8–72.4	70.1±1.2
Dorsal-fin base length	8.6	8.6–10.7	9.7±0.7
Adipose-fin base length	15.0	15.0–18.9	16.4±1.3
Anal-fin base length	8.1	8.1–10.5	8.9±0.9
Pelvic-fin length	17.9	16.6–21.3	19.2±1.7
Pectoral-fin length	20.9	19.9–24.9	22.5±2.1
Anal-fin length	15.7	15.7–19.3	17.7±1.8
Caudal-peduncle length	20.3	18.7–20.3	19.4±0.6
Caudal-peduncle depth	8.6	8.6–9.5	9.1±0.3
Anus to anal fin length	17.9	13.8–17.9	15.0±1.5
Prepelvic length	47.4	46.5–50.3	48.2±1.3
Postpelvic length	51.4	51.4–53.6	52.5±0.9
Dorsal-fin insertion to adipose	40.6	38.2–41.5	39.9±1.3
Dorsal-fin origin to caudal	64.5	62.2–66.2	64.1±1.5
Preanus length	53.7	53.7–58.9	56.3±1.8
%HL
Snout length	51.5	45.6–51.5	48.1±2.3
Interorbital distance	23.7	23.4–25.1	24.2±0.7
Maxillary barbel length	59.5	43.2–59.5	53.0±6.2
Inner mandibular barbel length	26.2	25.6–33.3	29.2±2.8
Outer mandibular barbel length	42.3	40.3–47.3	44.2±2.7
Eye diameter	12.7	11.6–14.3	12.8±0.8