Synodontis granulosus Boulenger, 1900

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 granulosus Boulenger, 1900

( Fig. 6; Supporting Information, Video S1)

Synodontis granulosus Boulenger, 1900: 480 (type locality: North end of Lake Tanganyika, Burundi or Democratic Republic of the Congo).

Materialexamined: Typematerial: BMNH 1906.9 .6.40, lectotype, S. granulosus , 213.1 mm SL, North end of Lake Tanganyika , Burundi /Zaire, coll. Moore. BMNH 1906.9.6.41–42, two, paralectotypes, S. granulosus , 180.0– 197.5 mm SL, North end of Lake Tanganyika , Burundi /Zaire, coll. Moore.

Non-type material: BMNH 1936.6.15.1199–1201, three, 161.2– 185.0 mm SL, Lake Tanganyika, coll. Christy. ISRNB 7085, one, 160.1 mm SL, Usumbura, Lake Tanganika, Burundi. MRAC 14157, one, 204.0 mm SL, Baie de Kilewa, Lake Tanganyika, Democratic Republic of the Congo, coll. Stappers. MRAC 14165, one, 178.0 mm SL, Baie de Kilewa, devant la Sambala, Lake Tanganyika, Democratic Republic of the Congo, coll. Stappers, 1912. MRAC 2001.094.P.0052, one, 84.5 mm SL, Mutondwe Island (Crocodile Island), Lake Tanganyika, Zambia, coll. Snoeks, Hanssens, Verheyen et al., 2001. MRAC 1982.012.P.0013–0015, three, 112.1–154.4 mm SL, Magara, Lake Tanganyika, Burundi, coll. Brichard, 1981. MRAC 1982.012.P.0016, one, 121.6 mm SL, Magara, Lake Tanganyika, Burundi, coll. Brichard, 1981. MRAC 1994.069.P.0289, one, 122.6 mm SL, Luhanga, ± 15 km S. d’Uvira, Lake Tanganyika, Democratic Republic of the Congo, coll. De Vos, 1994. MRAC 130378, one, 142.7 mm SL, Ile de Mboko, Lake Tanganyika, Democratic Republic of the Congo, coll. Matthes, 1958. NMW 100723, one, 90.2 mm SL, Mpulungu fish market, Lake Tanganyika, Zambia, coll. Reichard, Blažek, Zimmermann, Bartáková, 2022.

Diagnosis: Synodontis granulosus is distinguished from congeners in LT by a unique combination of characters: presence of a large axillary pore; abundant granular papillae on head, body, and fins; dorsal spine pigmented and completely dark; anal fin dark, posterior margin unpigmented and white; 38–49 (median 40) mandibular teeth, arranged in eight symmetric rows of replacement teeth; 90–152 (median 119) primary premaxillary teeth; 0–5 (median 0) secondary branches on inner mandibular barbels; and 41–45 (median 43) total vertebrae, with 22–25 (median 24) caudal vertebrae.

Description: The general appearance of S. granulosus is shown in Figure 6 and Supporting Information, Video S1; axial skeleton in Supporting Information, Figure S8B; and relative measurements, meristic counts, and coded characters are given in Supporting Information, Table S12.

Longest examined specimen 213.1 mm SL (female, BMNH 1906.9.6.40, lectotype). Body moderately compressed laterally. Dorsal head profile and predorsal back rising straight or convex to dorsal-fin origin in an angle of 23°–29° (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 greater than half of body depth at dorsal-fin origin. Head dorsoventrally compressed; depth at posterior eye margin almost equal to maximal cranium width. Snout blunt and usually shorter than half of head length. Mouth subterminal, with abundant papillae on lips; width 73.6%–90.8% of snout length. Eye diameter more than one-third of snout length.

Dense, granular papillae on head and body, also extending on fins. Occipitonuchal shield and humeral process deeply rugose and of granular texture. Humeral process usually narrow and elongated; maximal depth 20.4%–35.4% (N = 5) of its length. Large, conspicuous axillary pore at anterior ventral margin of humeral process.

Adipose fin usually well demarcated; basal length 23.7%– 34.6% of SL, extending over 51.3%–67.6% of distance between dorsal-fin insertion and end of caudal peduncle. Adipose-fin insertion distant to end of caudal peduncle. Dorsal fin with two unbranched and seven or eight branched rays; dorsal spine densely serrated on lower anterior edge, poorly marked serrations on upper anterior edge, posterior edge with 8–17 serrae; length of dorsal spine, excluding upper flexible part, 69.8%– 105.0% of head length and slightly longer than length of pectoral spine (excluding upper flexible part). Anal fin with commonly five unbranched and seven or eight branched rays; 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 densely serrated on anterior (17–38 serrae) and posterior (13–23 serrae) edges. Pectoral fin usually slightly shorter than pectoral–pelvic distance; in some specimens, tip of pectoral fin reaching above pelvic-fin origin in folded position. Caudal fin forked, with 2 + 15 principal rays; number of upper procurrent rays (9–14, median 12, N = 13) less than number of lower procurrent rays (10–16, median 15, N = 13).

Mandibular teeth 38–49 (median 40, N = 15) (lectotype 39), unicuspid, arranged in eight symmetric rows of replacement teeth. Primary premaxillary teeth 90–152 (median 119, N = 17) (lectotype 116), arranged in four or five irregular rows. Secondary and tertiary premaxillary teeth small, arranged in four and two rows, respectively.

Maxillary barbels long, usually reaching beyond pectoral-fin insertion. Outer mandibular barbels 28.8%–76.6% of head length, with 3–7 (median 5, N = 17) primary branches; secondary branches absent. Inner mandibular barbels with 5–9 (median 8, N = 17) primary branches and 0–5 (median 0, N = 17) secondary branches.

Total vertebrae 41–45 (median 43, N = 16) (lectotype 43), abdominal vertebrae 17–20 (median 19), preanal caudal vertebrae 3–4 (median 3), and postanal caudal vertebrae 19–22 (median 21).

In one specimen (90.2 mm SL), length of digestive tract (not stretched) ~59% of SL.

Coloration: In life (Supporting Information, Video S1), body coloration usually dark brown, dark grey, or black. Ventral side cream in colour, white, or greyish. Some individuals with black spots on lateral side and head, ventral side commonly without spots. Rayed fins pigmented and black, posterior margins unpigmented and white. Dorsal spine black. Lobes of caudal fin black, posterior margin white, narrow unpigmented edges at upper and lower margins. Maxillary and mandibular barbels white. Iris copper coloured.

In formalin (initial fixation) and later transferred to 75% ethanol ( Fig. 6A), coloration of body and fins similar to that in live specimens, but less whitish and more cream coloured. First branched dorsal-fin ray: 78% pigmented and dark (from base) vs. 22% unpigmented and cream coloured (from tip).

After long-term preservation in 75% ethanol ( Fig. 6B), historical specimens brown. Some specimens with dark spots on head, lateral side, and fins.

Distribution and habitat: Endemic to LT ( Fig. 1). Recorded over rocky benthic habitats between 18 m (Mahale National Park, Nganja point: H. Büscher, pers. comm.) and 130 m ( Coulter 1991). Synodontis granulosus appears to be more common in deep-water habitats, because the species was seen only twice in a depth shallower than 30 m during>800 SCUBA dives in Zambia and Tanzania between 2019 and 2023.