Synodontis polli Gosse, 1982

Englmaier, Gernot K., Blažek, Radim, Zimmermann, Holger, Bartáková, Veronika, Polačik, Matej, Žák, Jakub, Mulokozi, Deogratias P., Katongo, Cyprian, Büscher, Heinz H., Mabo, Lwabanya, Koblmüller, Stephan, Palandačić, Anja & Reichard, Martin, 2024, Revised taxonomy of Synodontis catfishes (Siluriformes: Mochokidae) from the Lake Tanganyika basin reveals lower species diversity than expected, Zoological Journal of the Linnean Society 202 (3) : -

Synodontis polli Gosse, 1982

( Fig. 11; Supporting Information, Video S5) Synodontis eurystomus Matthes, 1959: 77 (type locality: Luhanga , Lake Tanganyika, Democratic Republic of the Congo).

Synodontis polli Gosse, 1982: 48 , replacement name for Synodontis eurystomus Matthes, 1959 , preoccupied by Synodontis eurystomus Pfeffer, 1889 .

Synodontis ilebrevis Wright and Page, 2006: 117 (type locality: Chaitika , Lake Tanganyika, Zambia).

Material examined: Type material: MRAC130440 , holotype, S.polli , 123.7 mm SL, Luhanga , Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes, 1959 . MRAC 130441 , paratype, S. polli , 85.9 mm SL, Luhanga , Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes, 1959 . MRAC 130444–130446 , three, paratypes, S. polli , 78.7–119.0 mm SL, Makobola , Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes , 1958. MRAC 130464 , paratype, S.polli , 96.9 mm SL, Bemba , Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes , 1958. MRAC 130447–130451 , five, paratypes, S. polli , 57.6– 81.6 mm SL, Makobola , Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes, 1959 . MRAC 1978.025 .P.0020–0024, five, paratypes, S. ilebrevis , 77.9–112.4 mm SL, Cape Chaitika , Lake Tanganyika, coll. Brichard , 1978. UF 160942 , holotype, S. ilebrevis , 116.0 mm SL, Chaitika , Lake Tanganyika, Zambia, coll. Pete Hauschner, Tropical Fish Collector , 2005 (photographs and radiographs examined). UF 162562 , eight, paratypes, S. ilebrevis , 108.0–121.0 mm SL, Chaitika , Lake Tanganyika, Zambia, coll. Pete Hauschner, Tropical Fish Collector , 2005 (photographs and radiographs examined).

Non-type material: MRAC 2004.044 .P.0007, one, 97.0 mm SL, Jakobsen’s Beach, aka Mwamahunga, Kigoma, Lake Tanganyika , Tanzania, coll. Kazumbe , 2004. NMW 100727 , 15 , 74.1 – 131.0 mm SL, Mbita Island (8°45 ʹ 14.8″S, 31°05 ʹ 04.7″E), Lake Tanganyika , Zambia, coll. Reichard, Blažek, Zimmermann, Bartáková, Polačik , 2021. NMW 100728 , 16 , 68.0– 111.9 mm SL (and one C&S specimen in a separate jar, 80.8 mm SL, NMW 100784 ), Kalambo (8°37 ʹ 24.9″S, 31°11 ʹ 59.5″E), Lake Tanganyika , Zambia, coll. Reichard, Blažek, Zimmermann, Bartáková, Polačik , 2021. NMW 100729 , 15 , 58.4–101.1 mm SL, Cape Kachese (8°29 ʹ 18.6″S, 30°28 ʹ 32.3″E), Lake Tanganyika , Zambia, coll. Reichard, Zimmermann, Bartáková, Polačik , 2021. NMW 100730 , 15 , 70.4–102.3 mm SL, Mpende Fisheries (8°28 ʹ 56.9″S, 30°28 ʹ 00.1″E), Lake Tanganyika , Zambia, coll. Reichard, Zimmermann, Bartáková, Polačik , 2021. NMW 100731 , five, 81.7–93.7 mm SL, Katukula (8°43 ʹ 20.3″S, 30°56 ʹ 35.1″E), Lake Tanganyika , Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022. NMW 100732 , one, 113.0 mm SL, Hilltop cavesite(4°53 ʹ 11.01″S, 29°36 ʹ 47.22″E), Kigoma, LakeTanganyika , coll. Reichard, Zimmermann , 2022. NMW 100733 , two, 118.2– 129.2 mm SL, Nondwa Point (4°51 ʹ 50.1″S, 29°36 ʹ 28.6″E), Kigoma, Lake Tanganyika , coll. Reichard, Zimmermann , 2022. NMW 100734 , two, 92.9–109.3 mm SL, Nondwa Point (4°51 ʹ 50.1″S, 29°36 ʹ 28.6″E), Kigoma, Lake Tanganyika , coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100735 , one, 97.0 mm SL, Jacobson’s Beach (4°55 ʹ 3.00″S, 29°35 ʹ 44.01″E), Kigoma, Lake Tanganyika , coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100736 , seven, 78.5–113.6 mm SL, Cape Kabogo, site 1 (5°27 ʹ 42.45″S, 29°44 ʹ 50.19″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100737 , eight, 96.2–115.0 mm SL, Cape Kabogo, site 2 (5°28 ʹ 38.62″S, 29°45 ʹ 35.82″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100738 , 10 , 77.4–124.4 mm SL, Kalilani (6°0 ʹ 56.77″S, 29°44 ʹ 46.86″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100739 , 20 , 87.1–152.1 mm SL, Mabilibili (6°27 ʹ 26.51″S, 29°55 ʹ 2.41″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100740 , one, 92.3 mm SL, Karema (6°54 ʹ 57.18″S, 30°30 ʹ 1.66″E), Lake Tanganyika , Tanzania, Reichard, Blažek, Zimmermann, Englmaier, 2023 . NMW 100741 , nine, 119.6– 186.1 mm SL, Kibige (5°43 ʹ 8.06″S, 29°24 ʹ 38.73″E), Lake Tanganyika , Democratic Republic of the Congo, coll. Jiten Vaitha, Whiteboard Enterprises Ltd , 2022. NMW 100742 , one, 99.3 mm SL, Rutunga (3°38 ʹ 47.03″S, 29°20 ʹ 8.02″E), Lake Tanganyika , Burundi, coll. Jiten Vaitha, Whiteboard Enterprises Ltd , 2022.

Diagnosis: Synodontis polli is distinguished from congeners in LT by a unique combination of characters: axillary pore absent or macroscopically inconspicuous; no granular papillae on head, body, and fins; dorsal spine pigmented and dark, only the anterior edge unpigmented and white; anal fin dark, posterior margin unpigmented and white; 41–68 (median 53) mandibular teeth, arranged in eight symmetric rows of replacement teeth; 54–167 (median 94) primary premaxillary teeth; 0–8 (median 5) secondary branches on inner mandibular barbels; and 39–42 (median 40) total vertebrae, with 21–24 (median 23) caudal vertebrae.

Description: The general appearance of S. polli is shown in Figure 11 and Supporting Information, Video S5; axial skeletons in Supporting Information, Figure S8I, J; and relative measurements, meristic counts, and coded characters are given in Supporting Information, Table S12.

Longest examined specimen 186.1 mm SL (male, NMW 100741). Males usually larger than females (males 77.2– 186.1 mm SL, mean 111.0 mm, N = 61; females 58.9–138.1 mm SL, mean 90.1 mm, N = 76). Body shape variable (slender to deep bodied), moderately compressed laterally. Dorsal head profile and predorsal back rising straight or convex to dorsal-fin origin at an angle of 13°–22° (against midline of body). Postdorsal profile falling straight to adipose-fin origin and straight or slightly convex to caudal-fin origin. Body depth at anal-fin insertion commonly greater than half of body depth at dorsal-fin origin. Head dorsoventrally compressed; depth at posterior eye margin usually slightly smaller than maximal cranium width. Snout blunt, usually longer than half of head length. Mouth broad, subterminal with abundant papillae on lips; width 83.3%–118.0% of snout length. Eye diameter usually slightly larger than one-third of snout length.

Abundant villous papillae on head, body, and fins. Occipitonuchal shield and humeral process rugose and of granular texture. Humeral process short and deep; maximal depth 40.1%–52.7% (N = 9) of its length. Axillary pore absent or macroscopically inconspicuous, never large and prominent.

Adipose fin elongated; basal length 27.8%–43.1% of SL, extending over 52.8%–81.3% of distance between dorsal-fin insertion and end of caudal peduncle. Adipose-fin insertion close to end of caudal peduncle. Dorsal fin with two unbranched rays and commonly seven branched rays; dorsal spine moderately serrated on lower anterior edge, poorly marked serrations on upper anterior edge, posterior edge with 3–11 serrae; length of dorsal spine, excluding upper flexible part, 47.3%–97.0% of head length. Anal fin commonly with five unbranched rays and eight or nine branched rays; longest rays usually reaching beyond level of posterior edge of adipose fin. Pelvic fin with a single unbranched ray and six branched rays. Pectoral fin with a single unbranched ray and commonly nine branched rays; pectoral spine serrated on anterior (20–30 serrae) and posterior (10–18 serrae) edges. Pectoral fin shorter than pectoral–pelvic distance, and not reaching pelvic-fin origin in folded position. Caudal fin forked, with 2 + 15 principal rays; number of upper procurrent rays (11– 15, median 13, N = 31) less than number of lower procurrent rays (12–19, median 16, N = 33).

Mandibular teeth 41–68 (median 53, N = 153) (holotype of S. polli 62, holotype of S. ilebrevis 66), unicuspid, commonly arranged in eight (rarely six) symmetric rows of replacement teeth. Primary premaxillary teeth 54–167 (median 94, N = 153) (holotype of S. polli 111, holotype of S. ilebrevis 128), arranged in 3–5, commonly 4, irregular rows. Number of primary premaxillary teeth positively correlated with SL ( R = 0.50, Spearman’s rank correlation, N = 152). Secondary and tertiary premaxillary teeth small, arranged in two rows and one row, respectively.

Maxillary barbels short, commonly reaching beyond pectoral-fin origin (in 54 of 153 specimens shorter), but shorter than pectoral-fin insertion (only in 2 of 153 specimens longer). Outer mandibular barbels 31.9%–64.1% of head length, with 2–11 (median 5, N = 153) primary branches, secondary branches observed in only 20 specimens (N = 152). Inner mandibular barbels with 6–12 (median 8, N = 153) primary branches and 0–8 (median 5, N = 153) secondary branches.

Lateral-line canals ossified, extending beyond posterior margin of last complex centrum. One specimen (NMW 100784) with 69 ossified canals. Frontal fontanel (examined in one specimen, 80.8 mm SL, NMW 100784) originating at centre between eyes and extending beyond posterior margin of mesethmoid; shape oval, anterior and posterior margins round; length shorter than interorbital distance between frontal margins; resembling state B in paper by Pinton (2008: fig. 15).

Total vertebrae 39–42 (median 40, N = 95) (holotype of S. polli 41, holotype of S. ilebrevis 39), abdominal vertebrae 16–20 (median 18), preanal caudal vertebrae 2–4 (median 3), and postanal caudal vertebrae 18–21 (median 20).

Length of digestive tract (not stretched) ~182%–419% (mean 306%) of SL (N = 38, 73.1–131.0 mm SL).

Coloration: In life (Supporting Information, Video S5), body coloration variable, usually light brown or cream in colour, sometimes blackish or yellowish. Dorsal side darker than ventral side. Body usually covered with abundant black spots of variable size/shape (smallest on head), sometimes interspersed with smaller brown spots; a few specimens without spots. Rayed fins pigmented and black, posterior margins unpigmented and white. Dorsal and pectoral spines commonly black, with only their anterior edges unpigmented and white. Lobes of caudal fin with black bars, outer margins white. Maxillary and mandibular barbels white. Iris copper coloured.

In formalin (initial fixation) and later transferred to 75% ethanol ( Fig. 11), coloration similar to that in live specimens, commonly slightly darker. In 8% of specimens (N = 152), spots absent on ventral side. First branched dorsal-fin ray 59–94% (mean 72%, N = 45) pigmented and dark (from base) vs. 6%–41% (mean 28%) unpigmented and cream coloured (from tip).

After long-term preservation in 75% ethanol, historical specimens light brown, with dark brown spots on head, dorsal and lateral side of body, and adipose fin.

Distribution and habitat: Endemic to LT ( Fig. 1) but possibly also found in Lake Mweru Wantipa ( Schraml 2003a, Schäfer 2016). Commonly recorded from the rocky littoral zone. Can be found from very shallow water (0.5 m) down to 25 m in both the northern and southern lake basins, but most abundant at 5–10 m, where still abundant Aufwuchs is available. The species seems to be nocturnal and lives hidden in deep rocky crevices. It is found exclusively over rocky bottom, mainly where the habitat consists of several layers of large rocks. The only exception that we observed was at Mabilibili (central lake basin), where S. polli was highly abundant at 10–25 m in cracks of large limestone rocks scattered over sandy bottom.