Distichodus antonii Schilthuis, 1891: 89 Distichodus fasciolatus Boulenger, 1898 Distichodus langi Nichols and Griscom, 1917 A review of the Distichodus antonii assemblage (Characiformes: Distichodontidae) from the Congo basin Moelants, Tuur Zebe, Victorine Mbadu Snoeks, Jos Vreven, Emmanuel Journal of Natural History 2014 2014-03-03 48 27 - 28 1707 1735 36XL3 Schilthuis 1891 Schilthuis 1891 [427,820,248,272] Actinopterygii Distichodontidae Distichodus Animalia Characiformes 10 1716 Chordata species antonii    Distichodus fasciolatus Boulenger, 1898( partim): 27, pl. XIV.   Distichodus langi Nichols and Griscom, 1917( partim): 687–688.    Type material    Holotype. BMNH 1899.9.6.10, Kinshasa, Stanley Pool( DRC) (± 4°15′02″ S, 15°25′ 00″ E), coll. Greshoff, 1899 ( 103.3 mm SL).  Note on the   holotype.  Distichodus antoniiwas described by Schilthuisin 1891 based on a single specimen from “Bayari Sea”, collected by Greshoff( Schilthuis 1891). Fromthe introduction of Schilthuis’s article, it is clear that “Bayari Sea” is either situated near Kinshasa, or near Boma[ Lower Congo( DRC)]. Curiously, two specimensare labelled as type in the BMNH: a “ holotype” BMNH 1898.11.17.10 from “cataracts of Manyanga” with a size of 513.0 mm SL and a “type” BMNH 1899.9.6.10 from “Kinshasa, Stanley Pool” with a size of 103.3 mmSL ( 125.5 mm TL). The latter specimen and not the former clearly has to be considered as the  holotypeas it corresponds to the size ( 12.8 cm TL) given in the original description by Schilthuis (1891). We were unable to trace back the exact location of “Bayari Sea” and to the best of our knowledge this locality has nowhere else been used in the ichthyological literature of the Congo basin. Possibly, the widening of the Congo Riverchannel at Pool Malebo (Stanley Pool) has been called a “Sea” by the collector.  Table 4. Diagnostic characteristics of the species of the  Distichodus antoniiassemblage, with associated ranges, means (continuous variables) and medians (categorical variables).    Characteristic   D. antonii   D. fasciolatus   D. langi   D. atroventralis  complex  Mouth position terminal inferior inferior inferior  Internasal distance 10.1–26.5 (16.5) 8.1–21.0 (11.0) 14.4 & 15.9 7.6–21.3 (11.5)  (%HL)  Head depth (%HL) 35.2–67.2 (46.0) 35.9–62.9 (45.1) 67.4 & 69.4 35.1–55.7 (46.5)  LL scales in front of 52–64 (58) 61–70 (65) 68 & 70 61–76 (65–66)  HJ  Scales LL–dorsal fin 10–12 (11) 13–16 (14) 15 & 16 12–15 (13)  Scales LL–pelvic fin 10–11 (10) 10–12 (11) 12 9–11 (11)  Circumpeduncular 20–23 (22) 23–26 (24) 24 & 25 20–24 (22)  scales  Total dorsal fin rays 21–25 (23) 24–26 (25) 26 & 28 22–29 (23)  Total pectoral fin rays 16–20 (18) 17–20 (18) 21 17–20 (18)  Total pelvic fin rays 10–11 (10) 10–11 (10) 11 10–11 (11)  Number of vertical 9–14 (11) 13–20 (16) 13 6–-9 (7)  bars  Table 5. Morphometric and meristic data for  Distichodus antonii,  Distichodus fasciolatusand  Distichodus langi.    Morphometrics   Distichodus antonii   Distichodus fasciolatus   Distichodus langi  Holotype All specimens Lectotype All specimens Holotype MRAC 2878  min–max  n mean min–max  n mean  Standard length (mm) 103.3 24.8–416.0 50 120.2 278.2 55.7–445.0 34 135.6 364.0 300.0  Head length 27.2 8.4–98.6 50 30.7 57.2 14.9–106.6 34 31.1 75.6 65.8  As % of head length  Head depth 48.9 35.2–67.2 50 46.0 52.8 35.9–62.9 34 45.1 67.4 69.4  Snout length 33.1 22.6–41.9 50 32.2 36.2 24.9–40.4 34 31.5 42.6 41.5  Eye diameter 36.5 25.1–50.4 50 37.8 31.2 24.4–44.5 34 36.4 23.7 22.0  Postorbital length 32.9 26.3–39.2 50 31.7 34.3 29.5–42.9 34 34.8 38.2 35.0  Head width 46.4 36.1–63.5 50 47.5 50.6 34.6–58.5 34 44.2 52.5 55.6  Interorbital distance 42.3 18.1–52.4 50 38.0 39.0 23.6–42.8 34 32.4 44.7 46.1  Internasal distance 18.3 10.1–26.5 50 16.5 13.4 8.1–21.0 34 11.0 15.9 14.4  As % of standard length  Head length 26.3 22.5–34.0 50 26.7 20.6 20.3–26.7 34 23.7 20.8 21.9  Dorsal–pelvic fin distance 37.9 31.6–46.4 50 39.8 34.5 33.2–43.7 34 37.4 48.3 42.5  Predorsal distance 55.2 49.6–59.5 50 54.8 52.2 48.5–57.6 34 52.5 57.9 55.5  Prepectoral distance 27.2 23.1–33.3 50 27.2 21.8 21.8–28.4 34 24.6 20.4 22.0  Prepelvic distance 53.4 50.4–59.9 50 54.6 52.6 48.8–57.2 34 53.2 53.2 53.2  Preanal distance 82.0 77.3–91.3 50 83.9 79.2 73.0–90.5 34 79.8 77.8 80.3  Pectoral–anus distance 52.2 45.1–64.0 50 53.8 52.9 45.1–57.9 34 50.7 58.0 54.9  Pelvic–anus distance 25.5 21.0–33.6 50 26.8 21.1 18.6–25.8 34 21.7 25.9 23.4  Caudal peduncle length 8.6 3.7–10.3 50 7.2 10.9 5.9–11.9 34 9.0 9.9 13.8  Caudal peduncle height 13.7 11.9–19.0 50 13.9 11.0 10.5–15.8 34 11.9 17.4 15.9  Dorsal–adipose distance 11.1 8.3–13.1 50 10.9 14.4 12.6–17.1 34 14.5 15.0 14.9  Dorsal fin–CP distance 25.3 21.2–29.2 50 25.3 31.8 24.9–33.7 34 29.0 28.1 34.5  ( Continued)  Table 5. (Continued).    Morphometrics   Distichodus antonii   Distichodus fasciolatus   Distichodus langi  Holotype All specimens Lectotype All specimens Holotype MRAC 2878  min–max  n mean min–max  n mean  Dorsal fin base length 26.5 22.9–29.7 50 26.3 23.6 22.5–30.4 34 26.0 29.8 30.9  Dorsal fin height – 14.6–23.1 34 19.2 19.9 14.1–26.5 34 21.1 17.1 16.4  Anal fin base length 10.8 8.8–12.1 50 10.7 11.8 10.1–14.4 34 12.1 10.7 10.3  Anal fin height – 8.5–15.4 27 13.5 – 7.4–14.7 31 11.7 13.9 9.6  Pectoral fin base length 4.7 4.0–5.4 50 4.8 4.3 3.7–6.1 34 4.5 5.1 5.7  Pectoral fin length 15.8 12.3–20.4 50 18.2 16.2 13.7–20.5 33 17.7 19.5 19.7  Pelvic fin base length 4.0 2.8–6.0 50 4.3 4.6 3.2–5.6 4.5 5.3 5.3  Pelvic fin length 17.0 14.2–19.7 49 17.6 17.3 15.7–22.0 33 19.2 17.1 19.9  End pelvic fin–anus 6.4 3.9–18.0 48 8.7 2.9 -2.1–5.7 33 2.0 7.8 1. 6  distance  Meristics min–max  n mean min–max  n mean  LL scales in front of HJ 54 52–64 50 58 67 61–70 34 65 70 68  Scales LL–dorsal fin 10 10–12 50 11 13 13–16 34 14 16 15  Scales LL–pelvic fin 10 10–11 50 10 10 10–12 33 11 12 12  Circumpeduncular scales – 20–23 49 22 24 23–26 34 24 24 25  Total dorsal fin rays 24 21–25 44 23 25 24–26 34 25 28 26  Total anal fin rays 13 12–14 50 13 14 12–16 34 14 14 14  Total pectoral fin rays 18 16–20 50 18 18 17–20 34 34 21 21  Total pelvic fin rays 10 10–11 50 10 10 10–11 34 10 11 11  Number of vertical bars 12 9–14 40 11 – 13–20 23 16 - 13  Figure 3. Illustrations of type specimens of the  Distichodus antoniiassemblage. (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 4.  Distichodus antonii(B0-021-P-0873-0874) from the Loboya River, affluent of the Maiko River, Upper Congo (DRC), 89.4 mm SL. (A) Lateral view; (B) Detail of the colour pattern on the adipose fin.   Other material examined (all lengths are SL)   Distichodus antonii Schilthuis, 1891.  Democratic Republic of the Congo( DRC).  MRAC 88 Manyanga(± 4°54′ S, 14°23′E), coll. Wilverth1896 ( 279.9 mm).  MRAC 96, Léopoldville(± 4°18′ S, 15°18′ E), coll. Wilverth1896 ( 106.4 mm).  MRAC 2148, Léopoldville(± 4°18′ S, 15°18′ E), coll. Christy  30/06/1912(363.0 mm).  MRAC 2263, Léopoldville(± 4°18′ S, 15°18′ E), coll. Christy  7/05/ 1912(416.0 mm).  MRAC 2649, Stanley Pool(± 4°18′ S, 15°18′ E), coll. Dubois1912 ( 148.7 mm).  MRAC 2650. Léopoldville(± 4°18′ S, 15°18′ E), coll. Dubois1912 (362.0 mm).  MRAC 40938–40941, Léopoldville(± 4°18′ S, 15°18′ E), coll. Tinant  1/ 01/1934–  24/04/1934( 59.5–73.8 mm).  MRAC 67448–449, Léopoldville(± 4°18′ S, 15° 18′ E), coll. van Moorsel07/1944 ( 98.8–102.2 mm).  MRAC 48072, Kalamu river, near Boma(± 5°49′ S, 13°03′ E), coll. Dartevelle01/01/937–  4/08/1937( 181.2 mm).  MRAC 96207, Near Léopoldville(± 4°18′ S, 15°18′ E), coll. Vande Weyer1954 ( 58.4 mm).  MRAC 117317, Stanley Pool, Ndukaindigenous dam (± 4°20′ S, 15°24′ E), coll. MissionBrien-Poll-Bouillon,  23/09/1957( 211.3 mm).  MRAC 177320, Stanley Pool, meadows near Kingabwa(± 4°19′ S, 15°21′ E), coll. MissionBrien- Poll-Bouillon,  25/9/1957( 103.8 mm).  MRAC 177381, Stanley Pool(± 4°20′ S, 15°23′ E), coll. Van Orshoven  21/05/1964( 96.3 mm).  MRAC 177604–607, Stanley Pool(± 4°18′ S, 15°18′ E), coll. Brichard1967 ( 46.8–85.9 mm).  MRAC 73-22-P-1333, Stanley Pool(± 4°06′ S, 15°15′ Eand 4°20′ S, 15°23′ E), coll. Mandeville  22/09/1954( 24.8 mm).  MRAC 73-22-P-1335, Stanley Pool( DRC) (± 4°06′ S, 15°15′ Eand 4°20′ S, 15°23′ E), coll. Mandeville  24/11/1954(27.0 mm).  MRAC 73-22-P-1336- 337, Stanley Pool(± 4°06′ S, 15°15′ Eand 4°20′ S, 15°23′ E), coll. Mandeville  10/01/ 1955( 47.2–55.8 mm).  MRAC 73-22-P-1352, Stanley Pool(± 4°06′ S, 15°15′ Eand 4° 20′ S, 15°23′ E), coll. Mandeville  1/02/1958( 250.3 mm).  MRAC 86-21-P-30, Inga(± 5°39′ S, 13°39′ E), coll. Mutambwe Shango1967 ( 43.7 mm).  MRAC A7-014-P- 0002-0008, Pool Maleboat Kinkole, Molondo Island(± 4°16′47.8″ S, 15°27′59.7″ E), coll. Mbadu Zebe  29/12/2004( 85.4–139.7 mm).  MRACB0-021-P-0873-0874, Loboya River, right bank, Bambondji II, site 115 (± 0°11′33.1″ N, 25°31′50.1″ E), coll. Danaduand Moelants  31/08/2010( 85.5–89.4 mm).  MRACB0-021-P-0875, Lobaye River, right bank, Djabir, Site6B (± 0°29′28.1″ N, 24°10′42.8″ E), coll. Danaduand Moelants  9/08/ 2010( 153.2 mm).  MRACB0-021-P-0876-0877, Lomami River, left bank, Djabirsurroundings, site Lom2G2 (± 0°30′40.7″ N, 24°10′30.9″ E), coll. Danaduand Moelants  13/08/2010( 99.6–119.9 mm).  MRACB0-021-P-0878, Congo River, right bank, village Batikamondji I, site 101 (± 0°08′36.1″ N, 25°31′42.0″ E), coll. Danaduand Moelants  30/08/2010( 134.7 mm).  MRACB0-021-P-0879-0882, Loboya River, right bank, site 119B (± 0°11′27.0″ N, 25°31′39.7″ E), coll. Danaduand Moelants  31/ 08/2010( 115.3–130.3 mm). Paralectotypes  D. fasciolatus Boulenger, 1898:  MRAC 28, Boma( DRC) (± 5°50′ S, 13°03′ E), coll. Wilverth1896 ( 86.3 mm).  MRAC 63, Matadi( DRC) (± 5°49′ S, 13°27′ E), coll. Wilverth1896 ( 62.1 mm).  MRAC 102, Léopoldville( DRC) (± 4°18′ S, 15°18′ E), coll. Wilverth1896 ( 76.7 mm).    Republic of the Congo(Brazzaville). MRAC A4-046-P-1399-1407 (1/8), Kintelé, Congo River, (± 4°9.12′ S, 15°21.44′ E), coll. Mamonekene, Mady-Goma, Opoya et al.  19/6/2003, ( 95.7 mm).  MRAC A4-046-P-1438, Djoué River, tributary of Congo River, downstream from hydroelectric dam (± 4°19′ S, 15°14′ E), coll. Mamonekene, Bakabana, Ibala Zamba  24/7/2003( 180.5 mm).    Differential diagnosis Within the Congobasin,  D. antoniican be distinguished from  D. affinis,  D. altus,  D. decemmaculatus,  D. noboli,  D. notospilusand  D. teugelsiby its higher total number of LL scales, i.e. 52–64 (versus < 46 inthe six other species) and from  D. maculatusby the absence of large, dark spots all over the body (versus 9–14 vertical dark bars instead) and a higher number of dorsal fin rays, i.e. 21–25 (versus 19–21).  Distichodus antoniican be separated from all remaining Congospecies by its terminal (versus inferior) mouth, with the exception of  D. lusosso(which has a distinctive elongate snout and only six to eight vertical, dark bars) and by its low number of scales between the LL and the dorsal fin, i.e. 10–12 (versus 13–17) ( Table 4).    Description Morphometric and meristic data are given in Table 5. Body relatively deep (within  D. antoniiassemblage). 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 broad with nasal openings widely set apart (10.1–26.5 %HL), and head relatively shallow (35.2–67.2 %HL), although these characteristics are positively allometric. Mouth terminal. Posterior edge of maxillary not passing nostrils. Two rows of bicuspid teeth in each jaw. Origin of dorsal fin slightly in front of pelvic fin origin along vertical axis. Distal margin dorsal fin straight or slightly concave, distal margin of anal fin straight to slightly convex. Base and distal end of pelvic fin relatively far from vent; these distances are positive allometric, i.e. 21.0–33.6 %SL and 3.9–18.0 % SL, respectively. Pectoral and pelvic fin rays decreasing in length from outer to inner fin margin. Adipose fin situated approximately half-way between dorsal and caudal fins. Caudal peduncle deeper than long. Caudal fin forked with two rounded lobes covered with numerous small scales except for translucent distal area. Maximum reported total length 550 mm( Boulenger 1909). Duren (1943)stated it can reach a size of more than 800 mm.   Colouration Body in vivodark brown-olive, belly whitish. Dorsal fin scattered with numerous small, dark spots. Caudal fin dark brown or blackish. Adipose fin with a well-marked black distal margin ( Figures 3Aand 4). Pectoral fins uniform pale. Pelvic fins uniform pale or with slightly darker fin ray borders. Between 9 and 14 more or less distinct vertical dark bars on each flank that disappear with increasing size, starting to fade at c. 200 mmSL, disappearing at about 250 mmSL. Preserved specimens brownish with a lighter belly. The black margin of the adipose fin and vertical bars can be absent because of poor and/or long-term conservation.    Ecology According to Gosse (1963), the fry and juveniles of  D. antoniilive in aquatic prairies and in plant fringes. Adults feed in  Echinochloapatches and live at the edge of streams along islands and even on the bottom in the middle of the stream. The species is a phytophagous species; stomachs almost always contain plant fragments, with easily recognizable twigs and leaves of  Echinochloa, which comprises the largest part of their diet. The same author stated that this species has two annual periods of reproduction, and that like  Citharinusand all other  Distichodusspecies, spawning and egg deposition have to take place at the border of the stream, just before the flood. Recent results from stomach content analyses in Pool Malebo confirmed the all year round herbivorous diet of  D. antonii, mainly feeding on leaves, complemented with some detritus ( Mbadu Zebe et al. 2010a). Matthes (1964)reported the species as occurring in lakes and large rivers. Mbadu Zebe et al. (2010b)reported that low water levels during the dry season in Pool Malebo leads to the formation of scale annuli due to the scarcity of macrophytes (its main food source).    Distribution This species is a widespread Congobasin endemic ( Figure 5). Poll (1976)reported the species to be widespread in the Congobasin, including the Lualaba River, but absent from Luapula-Mweru. However, we found one specimen(MRAC 121238) from “Kasenga, Luapula River”, identified as  D. antoniiby Poll in 1959. We checked the identification and found it to be correct. As this specimen was originally registered as originating from “Kasenga, Lualaba”, a labelling error probably occurred. Therefore, we agree with Poll (1976)that  D. antoniiis absent from the Luapula system.  Distichodus antoniiseems to be sympatric with the  D. atroventraliscomplex,  D. fasciolatusand  D. langi. In recent collections (2010–2011) from the region of Kisangani, the first three taxa were even found syntopically in the same gillnet in all three possible combinations of two species.    Etymology   Distichodus antoniiwas most probably named by Schilthuis (1891)in memory of Anton Greshoff 1855–1905 ( Nieuw Letterkundig Magazijn 2010) who collected the holotype. SL Greshoff Democratic Republic of the Congo -4.2505555 Kinshasa 21 15.416667 Stanley Pool 10 1716 BMNH 1899.9 1 holotype BMNH, TL Schilthuis & Greshoff & From & Schilthuis' & Kinshasa & Boma & Curiously Democratic Republic of the Congo Lower Congo 10 1716 BMNH 1898.11, BMNH 1899.9 1 holotype TL Democratic Republic of the Congo Congo River 10 1716 1 holotype [144,1100,928,952] MRAC Wilverth -4.9 Manyanga 1306 14.383333 14 1720 MRAC 88 1 [144,1100,960,984] MRAC Wilverth -4.3 Leopoldville 1306 15.3 14 1720 MRAC 96 1 1912-06-30 MRAC Christy -4.3 Leopoldville 1306 15.3 14 1720 MRAC 2148 1 1912-05-07 MRAC Christy -4.3 Leopoldville 1306 15.3 14 1720 MRAC 2263 1 MRAC Dubois -4.3 Stanley Pool 1306 15.3 14 1720 MRAC 2649 1 MRAC Dubois -4.3 Leopoldville 1306 15.3 14 1720 MRAC 2650 1 1934-01-01 1934-04-24 1934-01-01 MRAC Tinant -4.3 Leopoldville 1306 15.3 14 1720 MRAC 40938-40941 1 MRAC van Moorsel -4.3 Leopoldville 1306 15.3 14 1720 MRAC 67448-449 1 1937-08-04 MRAC Dartevelle -5.8166666 Kalamu river 1305 13.05 Boma 14 1720 MRAC 48072 1 MRAC Van & Weyer -4.3 Near Leopoldville 1306 15.3 14 1720 MRAC 96207 1 1957-09-23 MRAC Mission -4.3333335 Stanley Pool 1306 15.4 Nduka 14 1720 MRAC 117317 1 1957-09-25 MRAC Mission & Poll-Bouillon -4.3166666 Stanley Pool 1306 15.35 Kingabwa 14 1720 MRAC 177320 1 1964-05-21 MRAC Van Orshoven -4.3333335 Stanley Pool 1306 15.383333 14 1720 MRAC 177381 1 MRAC Brichard -4.3 Stanley Pool 1306 15.3 14 1720 MRAC 177604-607 1 1954-09-22 MRAC Mandeville -4.3333335 Stanley Pool 1306 15.383333 14 1720 MRAC 73-22 1 1954-11-24 DRC Mandeville -4.3333335 Stanley Pool 1306 15.383333 14 1720 MRAC 73-22 1 1955-01-10 MRAC Mandeville -4.3333335 Stanley Pool 1306 15.383333 14 1720 MRAC 73-22 1 1958-02-01 MRAC Mandeville -4.3333335 Stanley Pool 1306 15.383333 14 1720 MRAC 73-22 1 MRAC Mutambwe Shango -5.65 Inga 1305 13.65 14 1720 MRAC 86-21 1 2004-12-29 MRAC Mbadu Zebe Molondo Island 15 1721 -4.279945 Pool Malebo 1 15.466583 Kinkole 14 1720 A7-014 1 2010-08-31 MRAC Bambondji II & Danadu & Moelants 0.19252779 Loboya River 1 25.530582 15 1721 1 2010-08-09 MRAC Danadu & Moelants Site 0.49113888 Lobaye River 1 24.178555 Djabir 15 1721 1 2010-08-13 MRAC Danadu & Moelants Lom 0.5113056 Lomami River 1 24.17525 Djabir 15 1721 1 2010-08-30 MRAC Batikamondji I & Danadu & Moelants 0.14336112 Congo River 1 25.528334 15 1721 1 2010-08-31 MRAC Danadu & Moelants 0.19083333 Loboya River 1 25.527695 15 1721 1 paralectotype DRC Wilverth -5.8333335 Boma 1305 13.05 15 1721 MRAC 28 1 paralectotype DRC Wilverth -5.8166666 Matadi 1305 13.45 15 1721 MRAC 63 1 paralectotype DRC Wilverth -4.3 Leopoldville 1306 15.3 15 1721 MRAC 102 1 paralectotype 2003-06-19 MRAC Mamonekene & Mady-Goma & Opoya Republic of the Congo -4.152 River 13 15.357333 Kintele 15 1721 A4-046 1 Bas-Congo 2003-07-24 MRAC Mamonekene & Bakabana & Ibala Zamba Republic of the Congo -4.3166666 River 1306 15.233334 Djoue River 15 1721 A4-046 1 Bas-Congo