Mastacembelus polli, Vreven, 2005

Vreven, E. J., 2005, Redescription of Mastacembelus ophidium Günther, 1893 (Synbranchiformes: Mastacembelidae) and description of a new spiny eel from Lake Tanganyika, Journal of Natural History 39 (18), pp. 1539-1560 : 1552-1557

Mastacembelus polli sp. nov.

( Figure 8 )

Synonyms and citations

Mastacembelus ophidium non Günther 1893 (in part): Günther 1893, p 630; Worthington and Ricardo 1936, p 1109; Matthes 1962, p 77 –80.

Mastacembelus sp. Poll 1953 , p 240, Figure 33C.

Type material

Only a small sample (i.e. the specimens> 95 mm TL) of the examined specimens identified as M. polli sp. nov. has been designated as type material of the new species. All specimens from Lake Tanganyika.

Holotype: MRAC 78-25 -P-41, Cap Kabeyeye ( Zambia) (¡8 ° 329S, 30 ° 439E), coll. P. Brichard, April 1978 (143 mm TL) . Paratypes: MRAC 128687 , Kalundu ( Democratic Republic of Congo) (¡3 ° 269S, 29 ° 089E), coll. H. Matthes (I. R.S.A.C.), 27 October 1960 (95 mm TL) . MRAC 128688 , Rumonge ( Burundi) (¡3 ° 589S, 29 ° 259E), coll. H. Matthes (I. R.S.A.C.), 24 November 1960 (95 mm TL) . MRAC 84-23 -P-638, 2me crique au N. de Masanza ( Democratic Republic of Congo) (¡7 ° 349S, 30 ° 139E), coll. P. Brichard, 13 June 1984 (144 mm TL) . MCZ 162850 (ex 50841), between Mutumba and Magara among rocks, depth 0–10 m ( Burundi) (¡3 ° 409S, 29 ° 209E), coll. D. J. Stewart, October 1973 (104 mm TL) . SAIAB 42477 , Musende Rocks ( Zambia) (¡8 ° 429S, 31 ° 079E), coll . R. Bills , 27 March 1993 (98 mm TL) .

Etymology

Named in honour of the late Prof. Dr M. Poll (1908–1991), a famous Belgian ichthyologist who pioneered ichthyological studies on Lake Tanganyika and who first drew attention to the fact that his Mastacembelus sp. ( Poll 1953) might well be a new species.

Diagnosis

Within Lake Tanganyika, M. polli sp. nov. can be distinguished from all other species, except M. ophidium , by a relatively long postanal length [50.6–56.6 (mean 53.7)% SL versus 53.5% SL or less] increasing with size (Figure 5a), which is longer than preanal length, itself being relatively short [42.7–47.6 (44.7)% SL versus 46.1% SL or more] and decreasing with size; by a relatively short distance from anterior border of snout to the last, externally visible, anal spine [45.9–51.3 (48.3)% SL versus 50.6% SL or more] (Figure 5b); and by protruding eyes, protruding lower jaw, ‘‘pointed’’ caudal fin, posterior angle of lips situated below eye, from about one-third of eye diameter, or even behind posterior border of eye (versus posterior angle of lips situated more anterior). From the highly similar M. ophidium it can be distinguished mainly by its smaller dorsal spine number [21+1 to 28+1 (median 24+1) versus 27+1 to 33+1 (28+1)], its smaller caudal vertebrae number [48–58 (53) versus 63–70 (66)], and its related smaller total vertebrae number [72–84 (77) versus 90–101 (95)].

Description

Meristics and morphometrics are given in Tables V and VI, respectively. The holotype is illustrated in Figure 8a–c .

Mastacembelus polli sp. nov. has protruding eyes, a small rostral appendage, a protruding lower jaw, a pointed caudal fin and a more elongated pectoral-fin shape (i.e. not so rounded as in many other species). Posterior angle of lips situated below the region from the middle of the eye up to a distance of about one-third of the eye diameter behind posterior border of eye. For the majority of the specimens the posterior angle of lips is situated below the posterior edge of the eye. Mastacembelus polli sp. nov. together with M. ophidium are the only African spiny eels in which the posterior angle of lips is situated so far posteriorly ( Figure 8b ). Upper corner of gill opening and dorsal edge of pectoral-fin base approximately at same level, clearly anterior to ventral edge of pectoral-fin base. Dorsal edge of pectoral-fin base situated above upper corner of the gill opening. Upper corner of gill opening situated between one-quarter and half (exceptionally three-quarters) of the vertical distance between the dorsal and ventral edge of pectoral-fin base ( Figure 8c ). Lateral line continuous from posterior border of head up to one-third or half of distance between head and anus, discontinuous more posteriorly.

Preanal length always shorter than postanal length; distance from anterior border of snout to last externally visible dorsal spine always longer than distance from anterior border of snout to last externally visible anal spine, and as a result origin of soft dorsal fin always posterior compared to origin of soft anal fin.

A relatively low number of dorsal spines, XXI+I to XXVIII+I, with spines increasing in size from first to last. Usually a very small almost entirely reduced spine hidden under the skin, and situated anterior to the base of the first dorsal-fin ray. Nevertheless, dorsal spine formula standardized as X+I.

One well-developed, externally visible anal spine. In addition, a very small almost entirely reduced spine, hidden under the skin, can be present, situated anterior to the base of the first anal-fin ray. First anal pterygiophore well developed, supporting only the first anal spine. Second anal pterygiophore very small, sometimes supporting an almost entirely reduced anal ‘‘spine’’. Nevertheless, the anal spine formula is standardized as I+I.

In all specimens the neural spine-supporting pterygiophore of the last externally visible dorsal spine and the haemal spine-supporting pterygiophore of the first anal spine are situated on two different vertebrae and are separated by one to five in-between vertebrae. The vertebra with the neural spine supporting the pterygiophore of the last externally visible dorsal spine is always situated posterior to the vertebrae whose haemal spine supports the first anal spine.

All specimens lack preopercular or preorbital spines.

Maximal observed standard length: 140 mm (144 mm TL).

Coloration ( Figure 8a )

Based on the holotype unless otherwise stated. Uniformly light brown overall background colour with numerous small, round, dark brown spots on dorsal part (approximately from around the lateral line up to more dorsal) of head, body and tail. Sometimes, spots larger and more irregularly shaped (MRAC 128687; MRAC 84-23- P-638) or less abundant and less contrasted with the overall background colour (MRAC 128688). Spots may be limited to three series, one on the dorsal midline and one on each lateral line (MRAC 128685–686). Some specimens only lack spots on tail region (MRAC 76-09-P-222–230: 107, 96, 92, 85, and 84 mm TL) whereas others entirely lack spots (MRAC 76-09-P-222–230: 104, 101, 75, and 72 mm TL). Background colour lighter, more yellowish white on lips, ventral region of head, belly and most ventral part of tail. Pectoral fins whitish transparent without spots. Dorsal, caudal and anal fins also whitish transparent.

Distribution (see Figure 9 )

Mastacembelus polli sp. nov. is endemic to Lake Tanganyika and appears to have a circumlacustrine shore distribution. However, it has not been found over large parts of the Tanzanian–Zambian and Democratic Republic of Congo coastline. I suspect this is due to poor sampling of these parts of the lake rather than to the real distribution of the species.

Mastacembelus polli sp. nov. was mentioned by Poll (1953) as rare.

Generic status

Similar to M. ophidium , M. polli sp. nov. is placed within the genus Mastacembelus .

Mastacembelus polli sp. nov. seems, based on the meristic, morphometric and colour pattern evidence, to be most closely related to M. ophidium . The more distant affinities of both species remain unresolved at present and need additional research.

Biology and ecology

Habitat. Coastal in distribution ( Poll 1953). For several specimens listed by Matthes (1962) additional information on the habitat of the material was provided: rocky bottom, flagstone; rocky bottom, rock slides and pebbles; and pebble bottom.

In addition, another sample of specimens was reported from a sandy bottom with snails, depth 20–40 m ( Matthes 1962). These specimens are most probably M. polli sp. nov. (23– 26 dorsal spines, according to Matthes 1962). Due to the small size of the latter material I was unable to make sharp X-rays, and make accurate counts of all vertebrae. Therefore, I consider the identification of the latter specimens as tentative. These specimens are the smallest ones reported for M. polli sp. nov.

Reproduction. According to Matthes two specimens of respectively 73.0 and 71.3 mm SL (see Matthes 1962, Table IX) were already recognizable as immature females ( Matthes 1962) (MRAC 128685–686, confirmed). Poll (1953) mentioned that the specimens he examined were obviously juveniles. Based on my own observations the holotype of M. polli sp. nov. and another specimen (MRAC 76-09-P- 222–230, 103 mm SL) are both nearly ripe females illustrating maturation at small size.

Fisheries and aquaculture

The capture method is variable ( Poll 1953).

Other specimens examined

All specimens from Lake Tanganyika.

Country unknown. BMNH 1936.6.15:1754–1756 (ex 1753–1756) (91–107 mm) ; BMNH 2003.3.23:1 (ex 1936.6.15:1757) (80 mm) .

Burundi. MRAC 76-09-P-222–230, côte Burundi (72–107 mm).

Democratic Republic of Congo. IRSNB 9438, Kalume, baie et rivière Lubumba, dist. Tanganyika, Congo Belge, Stat. 263, petite drague, baie à l’ancre (¡5 ° 209S, 29 ° 139E) (54 mm). MRAC 90974–90975, Stat. 93, baie de Bracone, ˆle ı de Kavala, senne (¡5 ° 389S, 29 ° 259E) (56–73 mm). MRAC 128685–686, Uvira (¡3 ° 249S, 29 ° 089E) (72–77 mm). MRAC 130719, Uvira, digue I.R.S.A.C. (¡3 ° 249S, 29 ° 089E) (70 mm).

Tanzania. BMNH 1889-1-30:24 (from 22–24) (paralectotype of M. ophidium ), near Ujiji (Udjidji ¡4 ° 569S, 29 ° 409E) (106 mm) . BMNH 1955.12.20:1687, Kala (¡8 ° 079S, 30 ° 589E) (49 mm) . IRSNB 9437 , Udjiji bords du lac et flaques de la plage , Tanganyika Territory (Ujiji ¡4 ° 569S, 29 ° 409E) (64 mm). SAIAB 56006 , Kigoma, Kigoma Bay below hill to Hotel (4 ° 539030S, 29 ° 379110E) (two specimens, 75–80 mm) . SAIAB 56008 , Kigoma, Jacobsen’s beach (4 ° 549310S, 29 ° 369020E) (76 mm) . SAIAB 70800 , Kigoma, Kigoma Bay below hill to Hotel (4 ° 539030S, 29 ° 379110E) (two specimens: 65–80 mm) .

Additional specimens (most probably M. polli sp. nov.). MRAC 128684 , Uvira ( Democratic Republic of Congo) (¡3 ° 249S, 29 ° 089E) (11 specimens, 45–55 mm) (only 11 of the 16 specimens as mentioned by Matthes 1962) .

Figures

Figure 8. Mastacembelus polli sp. nov., holotype, 143 mm TL, from ‘‘Cap Kabeyeye, Lac Tanganyika’’ (Zambia) (MRAC 78-25-P-41). (A) Lateral view. (B) Position of the posterior angle of lips to posterior nare and eye. Vertical line is perpendicular to a horizontal line parallel with upper surface of the head. (C) Detail of pectoral fin region. Upper tip of gill slit, dorsal edge of pectoral-fin base and ventral edge of pectoral-fin base connected by dashed lines.

Figure 9. Geographical distribution of Mastacembelus polli sp. nov. based on the localities of the examined specimens. (.) Holotype, (.) paratypes and (.) specimens of M. polli sp. nov.