Synodontis petricola Matthes, 1959

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 petricola Matthes, 1959

( Fig. 10; Supporting Information, Video S4) Synodontis petricola Matthes, 1959: 78 (type locality: Kashekezi, North Lake Tanganyika, Democratic Republic of the Congo). Synodontis lucipinnis Wright and Page, 2006: 126 (type locality: Musende Rocks, Lake Tanganyika, Zambia).

Material examined: Type material: MRAC 130357 , holotype, S. petricola , 79.5 mm SL, Kashekezi , North Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes, 1959 . MRAC 130368–130376 , seven, paratypes, S. petricola , 51.5–68.5 mm SL, Luhanga sud— Makobola, Lake Tanganika, Democratic Republic of the Congo, coll. Matthes, 1959 . MRAC 130361– 130367 , five, paratypes, S. petricola , 49.1–59.8 mm SL, Makobola , Lake Tanganika, Democratic Republic of the Congo, coll. Matthes, 1959 . BMNH 1936.6 .15.1232, one, paratype, S. petricola , 70.1 mm SL, Lake Tanganyika , coll. Christy. SAIAB 77880 , holotype, S. lucipinnis , 78.0 mm SL, Musende Rocks , Lake Tanganyika, Zambia, coll. Bills , 1992 (photographs and radiographs examined). SAIAB 39577 , six, paratypes, S. lucipinnis , 47.0–79.0 mm SL, Musende Rocks , Mpulungu, Lake Tanganyika, Zambia, coll. Bills , 1992 (photographs and radiographs examined). SAIAB 77879 , three, paratypes, S. lucipinnis , 56.0–69.0 mm SL, Musende Rocks , Lake Tanganyika, Zambia, coll. Bills , 1992 (photographs and radiographs examined). SAIAB 77882 , four, paratypes, S. lucipinnis , 44.0–78.0 mm SL, Musende Rocks , Lake Tanganyika, Zambia, coll. Bills , 1992 (photographs and radiographs examined). SAIAB 77894 , paratype, S. lucipinnis , 73.0 mm SL, Mbala , Mbita Island (northwest end), Lake Tanganyika, Zambia, coll. Bills, Schelly , 2004 (photographs and radiographs examined).

Non-type material: MRAC 2003.033 .P.0071–0074, four, 81.5– 89.1 mm SL, Mahumba , km 29 route Bujumbura-Nyanza, Lake Tanganyika, Burundi, coll. De Vos , 1994. NMW 100701 , five, 54.6–68.8 mm SL, Katete (8°19 ʹ 42.2″S, 30°31 ʹ 38.3″E), Lake Tanganyika , Zambia, coll. Reichard, Zimmermann, Bartáková, Polačik , 2021. NMW 100702 , four, 59.2–69.0 mm SL (and one C&S specimen in a separate jar, 66.0 mm SL, NMW 100783 ), Cape Kachese (8°29 ʹ 18.6″S, 30°28 ʹ 32.3″E), Lake Tanganyika , Zambia, coll. Reichard, Zimmermann, Bartáková, Polačik , 2021. NMW 100703 , five, 56.9–67.6 mm SL, Chimba Rocks (8°25 ʹ 13.4″S, 30°27 ʹ 41.8″E), Lake Tanganyika , Zambia, coll. Reichard, Zimmermann, Bartáková, Polačik , 2021. NMW 100704 , five, 60.6–70.6 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 100705 , 12 , 56.8–92.8 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 100706 , five, 62.7–76.2 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 100707 , three, 75.7–90.8 mm SL, Mbita Island (8°45 ʹ 14.8″S, 31°05 ʹ 04.7″E), Lake Tanganyika, Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022. NMW 100708 , five, 76.1–95.3 mm SL, Crocodile Island (8°42 ʹ 28.45″S, 31° 7 ʹ 17.82″E), Lake Tanganyika, Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022. NMW 100709 , four, 62.2–74.1 mm SL, Chituta Bay (8°43 ʹ 38.07″S, 31°9 ʹ 17.18″E), Lake Tanganyika, Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022. NMW 100710 , five, 49.6–78.5 mm SL, Kalambo (8°37 ʹ 24.9″S, 31°11 ʹ 59.5″E), LakeTanganyika , Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022. NMW 100711 , nine, 68.5–103.0 mm SL, Hilltop cave site (4°53 ʹ 11.01″S, 29°36 ʹ 47.22″E), Kigoma, Lake Tanganyika, Tanzania,coll. Reichard, Zimmermann ,2022. NMW 100712 , six, 73.5–107.3 mm SL, Nondwa Point (4°51 ʹ 50.1″S, 29°36 ʹ 28.6″E), Kigoma, Lake Tanganyika , Tanzania, coll. Reichard, Zimmermann , 2022. NMW 100713 , eight, 69.9– 111.0 mm SL, Nondwa Point (4°51 ʹ 50.1″S, 29°36 ʹ 28.6″E), Kigoma, Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100714 , six, 65.0– 91.7 mm SL, Jacobson’s Beach (4°55 ʹ 3.00″S, 29°35 ʹ 44.01″E), Kigoma, Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100715 , one, 114.2 mm SL, Hilltop (4°53 ʹ 18.37″S, 29°36 ʹ 41.05″E), Kigoma, Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100716 , one, 67.2 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 100717 , one, 80.7 mm SL, Cape Kabogo, site 3 (5°30 ʹ 9.56″S, 29°47 ʹ 14.94″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100718 , 10 , 62.3–92.2 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 100719 , 10 , 60.7–87.4 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 100720 , one, 90.5 mm SL, Karema (6°54 ʹ 57.18″S, 30°30 ʹ 1.66″E), Lake Tanganyika , Tanzania, coll. Reichard, Blažek, Zimmermann , Englmaier, 2023. NMW 100721 , one, 67.0 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 100722 , one, 56.4 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 petricola 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 commonly unpigmented and white; anal fin dark, posterior margin unpigmented and white; 31–48 (median 39) mandibular teeth, commonly arranged in six symmetric rows of replacement teeth; 31–97 (median 51) primary premaxillary teeth; 1–11 (median 6) secondary branches on inner mandibular barbels; and 38–42 (median 39) total vertebrae, with 20–23 (median 22) caudal vertebrae.

Description: The general appearance of S. petricola is shown in Figure 10 and Supporting Information, Video S4; axial skeletons in Supporting Information, Figure S8G, H; and relative measurements, meristic counts, and coded characters are given in Supporting Information, Table S12.

Longest examined specimen 114.2 mm SL (male, NMW 100715). Males usually larger than females (males 49.6– 114.2 mm SL, mean 81.0 mm, N = 57; females 49.8–89.1 mm SL, mean 68.5 mm, N = 54). Body slender, exhibiting moderate dorsoventral compression. Dorsal head profile and predorsal back usually rising straight to dorsal-fin origin at an angle of 13°–18° (against midline of body). Postdorsal profile falling straight to adipose-fin origin, 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 smaller than maximal cranium width. Snout blunt and usually longer than half of head length. Mouth subterminal, with abundant papillae on lips; width 81.6%–126.7% of snout length. Eye diameter usually one-third of snout length.

Head, body, and fins with few, scattered, non-granular papillae, densest on head. Occipitonuchal shield and humeral process rugose and of granular texture. Humeral process narrow; maximal depth 21.6%–33.8% (N = 9) of its length. Axillary pore absent or macroscopically inconspicuous, never large and prominent.

Adipose fin elongated; basal length 27.7%–43.7% of SL, extending over 51.3%–79.2% 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 poorly serrated on lower and upper anterior edges, posterior edge with 5–9 serrae; length of dorsal spine, excluding upper flexible part, 53.5%–84.7% of head length. Anal fin commonly with five unbranched rays and eight or nine branched rays; in 65% of specimens (N = 127), longest rays 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 eight branched rays; pectoral spine serrated on anterior (15–21 serrae) and posterior (8–13 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 (11–14, median 13, N = 29) less than number of lower procurrent rays (12–18, median 14, N = 39).

Mandibular teeth 31–48 (median 39, N = 127) (holotype of S. petricola 44, holotype of S. lucipinnis 47), unicuspid, commonly arranged in six (rarely four or eight) symmetric rows of replacement teeth. Primary premaxillary teeth 31–97 (median 51, N = 128) (holotype of S. petricola 47, holotype of S. lucipinnis 68), commonly arranged in two or three (rarely four) irregular rows. Secondary and tertiary premaxillary teeth small, arranged in two or three rows and one row, respectively.

Maxillary barbels short, reaching beyond pectoral-fin origin (in 11 of 128 specimens shorter), but only in 34 of 128 specimens reaching beyond pectoral-fin insertion. Outer mandibular barbels 36.4%–63.3% of head length, with 3–11 (median 5, N = 128) primary branches, secondary branches observed in only 25 specimens (N = 127). Inner mandibular barbels with 5–14 (median 9, N = 128) primary branches and 1–11 (median 6, N = 128) secondary branches.

Lateral-line canals ossified, extending beyond posterior margin of last complex centrum. One specimen (NMW 100783) with 70 ossified canals. Frontal fontanel (examined in one specimen, 66.0 mm SL, NMW 100783) originating at centre between eyes and extending beyond posterior margin of mesethmoid; shape broad oval, anterior and posterior margins roundish; length slightly shorter than interorbital distance between frontal margins; resembling state B in the paper by Pinton (2008: fig. 15).

Total vertebrae 38–42 (median 39, N = 96) (holotype of S. petricola 40, holotype of S. lucipinnis 38), abdominal vertebrae 16–20 (median 18), preanal caudal vertebrae 2–4 (median 3), and postanal caudal vertebrae 17–21 (mode 19).

Length of digestive tract (not stretched) ~152%–226% (mean 185%) of SL (N = 17, 56.0–109.0 mm SL).

Coloration: In life (Supporting Information, Video S4), body coloration usually light brown or cream coloured, sometimes yellowish or black–grey. Dorsal side darker than ventral side. Body covered with abundant black spots of variable size/shape; spots smallest on head. Some specimens with small interspersed brown spots. Rayed fins pigmented and black, broad posterior margins unpigmented and white. Dorsal and pectoral spines and unbranched pelvic-fin ray unpigmented and white. Base of rayed fins frequently with unpigmented blotches of variable size/ shape. Lobes of caudal fin with black bars, outer margins white. Maxillary and mandibular barbels white, sometimes greyish. Iris copper coloured.

In formalin (initial fixation) and later transferred to 75% ethanol ( Fig. 10), coloration similar to that in live specimens, commonly darker. In 2% of specimens (N = 126), spots absent on ventral side. First branched dorsal-fin ray: 87%–100% (mean 97%, N = 37) pigmented and dark (from base) vs. 0%–13% (mean 3%) unpigmented and cream coloured (from tip).

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

Distribution and habitat: Endemic to LT ( Fig. 1). Synodontis petricola was frequently observed below 15 m. A completely dark phenotype of S. petricola ( Fig. 10C) was found in shallow water (1–10 m) only in the southern lake basin (sampling sites: Kalambo and Mbita Island). Based on our observations, S. petricola is more associated to rocky habitats than S. multipunctatus , but even small crevices of small- to mediumsized stones provide enough shelter for this species. Coherent rock coverage and only little sandy interstices seem to be preferred. The species can also be found in scattered rock fields over sand, where it often uses burrows of small Lamprologine cichlids to hide. In suitable habitats, S. petricola appears to be the most numerous Synodontis species in LT, but in less suitable areas it is almost entirely absent.