Distichodus fasciolatus Boulenger, 1898

Moelants, Tuur, Zebe, Victorine Mbadu, Snoeks, Jos & Vreven, Emmanuel, 2014, A review of the Distichodus antonii assemblage (Characiformes: Distichodontidae) from the Congo basin, Journal of Natural History 48 (27 - 28), pp. 1707-1735 : 1723-1726

Distichodus fasciolatus Boulenger, 1898

( Tables 4 and 5; Figures 3B and 6 )

Distichodus fasciolatus Boulenger, 1898: 27 , pl. XIV.

Distichodus langi Nichols and Griscom, 1917 (partim): 687–688.

Type material (all lengths are SL)

Lectotype. MRAC 23 , Boma ( DRC) (± 5°50′ S, 13°03′ E), coll. Wilverth 1896 (278.2 mm SL)

Paralectotypes. MRAC 98 , 99 , Léopoldville ( DRC) (± 4°18′ S, 15°18′ E), coll. Wilverth 1896 (113.9 mm; 111.0 mm) . MRAC 150 , Upoto ( DRC) (± 2°09′ N, 21°30′ E), coll. Wilverth and Wagenaar 1896 (88.0 mm) . MRAC 737 , Léopoldville ( DRC) (± 4° 18′ S, 15°18′ E), coll. Delhez 1899 (86.3 mm) . BMNH 1891.12 .29.22–23, Congo River ( DRC), coll. received from Utrecht university museum 1891 (55.7 mm; 61.1 mm) . BMNH 1898.7 .9.19, Congo River , Monsémbé ( DRC) (± 1°15′ S, 18°38′ E), coll. Weeks 1898 (114.4 mm) . BMNH 1898.11 .17.13, Boma , Lower Congo ( DRC), coll. received from the Secretary of State Congo Free State 1898 (211.8 mm) . BMNH 1898.11 .17.14, Cataracts of Manyanga ( DRC) (4°54′ S, 14°23′ E), coll. received from the Secretary of State Congo Free State 1898 (170.3 mm) .

Note on the type specimens. The 13 syntypes of D. fasciolatus housed at RMCA and the BMNH originate from the Lower Congo (Matadi, Boma and Manyanga cataracts), and the Central Congo [Kinshasa (formerly Léopolville), Monsembé and Upoto]. Three syntypes ( MRAC 28, 63 and 102) were found to be D. antonii and are therefore listed with D. antonii .

Because of the polyspecificity of the type series, the syntype MRAC 23, used in the original description of Boulenger (1898) to illustrate D. fasciolatus , is here designated as the lectotype. As such, all other syntypes of D. fasciolatus become paralectotypes.

Other material examined (all lengths are SL)

Distichodus fasciolatus Boulenger, 1898 . Democratic Republic of the Congo ( DRC). MRAC 744 /A, Kutu (± 2°44′ S, 18°08′ E), coll. Dehlez 1899 (445.0 mm) – MRAC 2439 , Léopoldville (± 4°18′ S, 15°18′ E), coll. Christy 1913 (77.7 mm) – MRAC 99075 , Stanley Pool (± 4°06′ S, 15°15′ E and ± 4°20′ S, 15°23′ E), coll. Mandeville 10/ 7/1955 (116.2 mm) . MRAC 117371 , Stanley Pool , channel in front of Maluku (± 4° 04′ S, 5°33′ E), coll. Mission Brien-Poll-Bouillon 4/10/1957, Poll M., 1958 (66.5 mm) . MRAC 91-013 -P-0574-0575, Nsele River ( Benzale ) a tributary of Congo River near Kinshasa (± 4°08′ S, 15°40′ E), coll. Tshibwabwa Sinaseli 1985 (93.8 mm; 101.4 mm) . MRAC A7-14 -P-0009-0018, Pool Malebo at Kinkole, Japon island (± 4°18′26.9″ S, 15°30′33.7″ E), Mbadu Zebe 22/2/2007 (63.3–139.2 mm) . MRAC A7-14 -P-0019-0021. Pool Malebo at Kinsuka, Mimosa island (± 4°20′ S, 15°13′ E), coll. Mbadu Zebe 15/ 8/2006 (208.1–252.8 mm) . MRAC A7-14 -P-0022-0024, Pool Malebo at Kinkole, Japon island (± 4°22′17.7″ S, 15°30′46.0″ E), Mbadu Zebe 25/2/2007 (98.4– 119.6 mm). Distichodus langi Nichols and Griscom, 1917 . AMNH 7010 , Faradje (± 3°44′ N, 29°43′ E), coll. Lang-Chapin 1909–1915 (250.7 mm) .

Republic of Angola. MRAC 158807 , Dundo , in the rapids of the Luachimo River (± 7°21′ S, 20°50′ E), coll. Indigenous collect 20/10/1955 (316.0 mm) .

Differential diagnosis

Within the Congo basin, D. fasciolatus can be distinguished from D. affinis , D. altus , D. decemmaculatus , D. noboli , D. notospilus and D. teugelsi by its higher total number of LL scales, i.e. 61–70 (versus <46 in the six other species) and from D. maculatus by the absence of large, dark spots all over the body (13–20 vertical dark bars instead) and a higher number of dorsal fin rays, i.e. 24–26 (versus 19–21). It can be distinguished from D.antonii by its inferior mouth (versus terminal) and its higher number of scales between the LL and the dorsal fin, i.e. 13–16 (versus 10–12); from D. lusosso by its inferior mouth (versus terminal), its feebly compressed snout (versus distinctively prolonged), and its higher number of dark vertical bars along the body, at least in specimens ≤ 150 mm SL, i.e. 13–20 (versus 6–8); from D. sexfasciatus by its higher number of teeth on the outer row on both jaws, i.e. 20–30 (versus 12–18); its higher number of dark vertical bars on the flanks, at least in specimens ≤ 150 mm SL, i.e. 13–20 (versus 6–8) and its brownish-yellowish colouration (versus orange-reddish to red). Moreover, D. fasciolatus can be differentiated from both the D. atroventralis complex and D. langi by its lower number of pelvic fin rays, i.e. 10, exceptionally 11 (versus 11, exceptionally 10 for the D. atroventralis complex and always 11 for D. langi ); from the D. atroventralis complex by its higher number of dark vertical bars, at least in specimens ≤ 150 mm SL, i.e. 13–20 (versus 6–9) and presence of pale pelvic fins, at least in specimens of ≤ 200 mm SL (versus blackish) and from D. langi by a combination of characteristics: 24–26 total dorsal fin rays (versus 26–28) and a lower head depth, i.e. 35.9–62.9% HL for specimens of comparable size (versus 67.4–69.4 % HL) ( Table 4).

Description

Morphometric and meristic data are given in Table 5. Body relatively shallow (within D. antonii assemblage). Dorsal head profile straight, dorsal body outline concave from posterior to head to end of dorsal fin, straight from end of dorsal to adipose fin, and convex from adipose to caudal fin. Ventral head profile straight, concave from posterior to head to end of anal fin, and convex from end of anal to caudal fin. Head compressed with nasal openings relatively closely set (8.1–22.0 %HL), and head relatively shallow (35.9–62.9 %HL), although these characteristics are positively allometric. Mouth inferior. Posterior edge of maxillary not passing nostrils. Two rows of bicuspid teeth in each jaw. Origin of dorsal fin well in front of pelvic fin origin along vertical axis. Distal margin of dorsal fin straight or slightly concave, distal margin of anal fin straight to slightly convex. Base and distal end of pelvic fin relatively close to vent, although these distances are positive allometric, i.e. 18.6–25.8 %SL and – 2.1–5.7 %SL, respectively. Pectoral and pelvic fin rays decreasing in length from outer to inner fin margin. Adipose fin approximately half-way between dorsal and caudal fins. Caudal peduncle deeper then long or as deep as long. Caudal fin forked with superior lobe slightly pointed and inferior lobe rounded, covered with numerous small scales except for the translucent distal area.

Maximum recorded length: 600 mm TL ( Daget and Gosse 1984).

Colouration

Small-sized specimens (c. 122–150 mm SL) in vivo are brown-yellowish on the flanks with copper-coloured reflections and with 13–20 dark vertical bars on the flanks. Dorsal fin scattered with many small, dark spots. Caudal fin with a discrete black outer edge. Adipose fin with no or only a very thin greyish distal margin ( Figures 3B and 6 ). Pectoral fins pale. Pelvic fins generally pale, sometimes with slightly darker distal margins. Dark spot above the pectoral fin and at the base of the caudal fin. Larger specimens (c. 300 mm SL) are brownish, the transverse bars on the flanks as well as the dark spots above the pectoral fin and the root of the caudal fin can become vague but the marks on the dorsal fin clearly remain. Small preserved specimens are brownish with a silvery whitish belly; larger specimens (c. 450 mm SL) are uniformly brownish.

Ecology

According to Gosse (1963), D. fasciolatus is a bottom-dweller in streams. The fry are born near the river banks just before the April or December floods and feed on zooplankton and insect larvae in the flooded zones; adults mainly feed on insect larvae, aquatic plants, leaves and seeds. Fry were observed on the border of the stream just before the flood, spending the first few months in the flooded forest, before returning to the Echinochloa fields. Matthes (1964) considered this species as mainly herbivorous; the specimens he examined had sand, filamentous algae and plant debris in their stomachs, with some nematodes and insect debris (Ephemeroptera larvae, Trichoptera and small Dytiscidae ). He also stated that D.fasciolatus is found near the muddy bottom in lakes, large rivers and their dead-ending branches. Recent stomach content analyses on specimens from the Lomami and Maiko rivers (Kisangani region) confirmed this mainly herbivorous diet, though insects were also found in the stomachs (Vanstallen, pers. obs.).

Distribution

This species is a widespread Congo basin endemic ( Figure 7 ). One specimen (RBINS no. 9067) from a market in Albertville (Kalemie), Lake Tanganyika has been identified as D. fasciolatus by Poll (1953) and its identification confirmed by us. Poll (1953) stated that the species’ discovery at Albertville is probably caused by a recent and rare migration through the Lukuga River. Another plausible explanation, however, might be that since the specimen was bought at a local market, it has not been caught in Lake Tanganyika itself, but in adjacent rivers from the Congo basin, such as the Lukuga River.

Etymology

The species name “ fasciolatus ” is derived from the Latin word “ fascia ”, meaning “band, bandage, girdle, zone, strip, stripe” with “ fasciola ” as a diminutive ( Brown 1956) and most probably refers to the well-marked transverse bars on the flanks.

Figures

Figure 3. Illustrations of type specimens of the Distichodus antonii assemblage. (A) Holotype of D. antonii (BMNH 1899.9.6.10), 103.3 mm SL; (B) Lectotype of Distichodus fasciolatus (MRAC 23), 278.2 mm SL; (C) Holotype of Distichodus langi (AMNH 5915), 364 mm SL. Picture taken by M.L.J. Stiassny (AMNH); (D) Syntype of Distichodus atroventralis (BMNH 1891.12.29.13), 63.5 mm SL.

Figure 6. Distichodus fasciolatus (A7-014-P-0009-0018) from Pool Malebo (DRC), 100.9 mm SL. (A) Lateral view. (B) Detail of the colour pattern on the adipose fin.

Figure 7. Distribution map of Distichodus fasciolatus based on the specimens identified at the AMNH and MRAC. () lectotype and (●) other specimens.