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