Marcusenius macrolepidotus ( Peters, 1852 )

Kramer, Bernd, Skelton, Paul, Bank, Herman Van Der & Wink, Michael, 2007, Allopatric differentiation in the Marcusenius macrolepidotus species complex in southern and eastern Africa: the resurrection of M. pongolensis and M. angolensis, and the description of two new species (Mormyridae, Teleostei), Journal of Natural History 41 (9 - 12), pp. 647-708 : 677-680

Marcusenius macrolepidotus ( Peters, 1852)

( Figures 1A, H )

Nominal species in boldface.

Mormyrus macrolepidotus Peters, 1852 a, p. 275 .

Mormyrops macrolepidotus: Marcusen 1864, p. 142 .

Gnathonemus macrolepidotus: Boulenger 1898, p. 804 .

Gnathonemus macrolepidotus macrolepidotus: Poll and Gosse 1963, p. 93 .

Marcusenius macrolepidotus: Taverne 1971a, p. 103 .

Gnathonemus okavangensis Pappenheim 1907, p. 354 , nomen dubium.

Gnathonemus moeruensis Boulenger, 1915, p. 163 ; Jackson 1961, p. 32 (most probably a subspecies of Gnathonemus macrolepidotus ) (type locality, no. 3, Figure 4 ).

Marcusenius moeruensis: Taverne 1971a, p. 102 .

Gnathonemus graeverti Steindachner, 1914, p. 536 (in full Steindachner 1916); Matthes 1967, p. 4 (synonymy with Gnathonemus macrolepidotus ).

Marcusenius graeverti: Taverne 1971a, p. 103 .

Type specimens. ZMB 3678 (lectotype L. Seegers 13.04.1993) from Tete, Lower Zambezi , Mozambique, with paralectotypes ZMB 6730 (one specimen), 3677 (one specimen), and 32043 (three specimens; Seegers 1996) .

Type locality. Mozambique: Lower Zambezi: Tete (no. 1, Figure 4 ), and tributaries to the Lower Zambezi, also Licuare River (Zambezi delta region) .

For a type locality, Peters (1852) gives no more detail than ‘‘riverine fishes from Mozambique’’ (as per title). In his more detailed 1868 publication, Peters specifies the ‘‘ Zambezi and its tributaries’’ (‘‘… in dem Zambeze und seinen Nebenflüssen’’), and on p. 83 the township of ‘‘Tette’’ (modern spelling Tete; locality 1 on Figure 4 ) on the Lower Zambezi, 400 km from the Indian Ocean (‘‘Tette’’ is also marked outside and inside the jars holding the type material). As an additional origin Peters (1868) gives the Licuare River which is a small coastal river flowing into the Indian Ocean at the township of Quelimane, at the northern range of the Zambezi Delta.

Since Taverne’s (1971b) major revision of several genera of the Mormyridae , there are no members of Gnathonemus in southern Africa. Presently, two subspecies of M. macrolepidotus are recognized ( Poll and Gosse 1963): M. m. macrolepidotus and M. m. angolensis , listed by Gosse (1984) and Eschmeyer (2006). Based on morphology (Table XI), we resurrect the latter subspecies as a valid species, and in consequence drop the former subspecies. The origin of G. moeruensis Boulenger 1915 , a single specimen from Lake Mweru in the Democratic Republic of Congo ( Zaïre)/ Zambia, west of Lake Tanganyika (locality 3 on Figure 4 ), forms part of the Lualaba/ Congo drainage system, and from morphology the synonymization appears questionable to the present authors (Table XI). Also synonymized with G. macrolepidotus was G. graeverti Steindachner 1914 whose origin is the Ruaha, an east-flowing river south of Daressalaam, Tanzania; the unique holotype is lost (from its SPc of 12 and an SLS of 69–70 as given in the original description the synonymization is questionable, and also the geographically closer M. devosi and Rovuma samples do not match). Gnathonemus pongolensis Fowler 1934 is still another relegated species based on a single specimen from the Pongola River in KwaZulu-Natal / South Africa, a species that is resurrected below (locality 4 on Figures 4 and 8 ). Gnathonemus okavangensis Pappenheim 1907 is ‘‘not available’’ (see below under the heading M. altisambesi ).

Diagnosis. Marcusenius macrolepidotus is best distinguished from M. altisambesi by its median SPc of 16 (12–18) vs. 12 (12–14), and EOD lacking an initial head-negativity; from M. devosi by a median SLS of 55.5 (52–62) vs. 62.5 (56–66), shorter CPL (mean 18.8% vs. 20.2% of SL), and weaker Namp of its EOD (mean 21.1¡SE 0.019 normalized volts vs. 21.39¡SE 0.023 V; from M. pongolensis by a median SLS of 55.5 (52–62) vs. 73 (70–76), a median SPc of 16 (12–18) vs. 18.5 (16–20), greater BD of 26.5% vs. 24.7% of SL, longer Ndur of its EOD in females and juveniles (174¡SE 5 Ms vs 140¡SE 3 Ms); from M. angolensis by its lower nA (ǩ29 vs. 33) and nD (ǩ24 vs. 26), and higher SPc (a median of 16 vs. 12).

Description. For a detailed description, see Peters (1868, pp. 79–83). Since several similar species have now been recognized that have routinely been considered M. macrolepidotus , additional description seems necessary. Head with terminal mouth well in front of eye, mental lobe on lower jaw protruding beyond upper jaw. Head and body dorsolaterally compressed. Dorsal fin situated about two thirds of standard length from snout, obliquely orientated, anteriorly higher and posteriorly lower, proximal tip rounded, distal tip sharply pointed, distal margin sometimes only slightly crescentic with anterior two or three rays longer than posterior rays, number of rays 20 (N 56), 21 (N 527), 22 (N 537), 23 (N 513), 24 (N 53); anal fin opposite dorsal fin with distinctly more anterior origin, obliquely orientated, anteriorly lower and posteriorly higher, anterior rays longer than posterior ones, especially in males where they also appear stronger and often darkened, distal margin crescentic (in males only posterior to rounded, elongated anterior part of fin), number of rays 26 (N 56), 27 (N 530), 28 (N 537), 29 (N 510), 30 (N 52), 31 (N 51). Scales cycloid with reticulate striae, scales extending anteriorly to operculum and pectoral fins (beyond pelvics). Scales on caudal peduncle circumference, 12 (N 52), 13 (N 52), 14 (N 515), 15 (N 511), 16 (N 552), 17 (N 51), 18 (N 51). Caudal peduncle relatively deep, subcylindrical entire length, usually 19% (17–21%) in SL. Colour in life (determined from five fish originating from the Buzi River): back and sides grey-silver, dark on the back and lighter on the sides, to very fair on the underside, gold-olive or purple shimmer depending on angle of light incidence, dark-grey blotches on sides and on unpaired fins, especially on the tail, but absent on head and belly, area next to first ray of anal fin darker, less distinct in females. Electric organ discharge biphasic lacking a weak pre-potential, Pdur around 183 Ms (at 25 u C and ‘‘5% threshold criterion’’), Ndur around 174 Ms, Pamp and Namp of similar strength. No sexual dimorphism in EOD recognized. Males approaching sexual maturity develop a kink in the base of the anal fin which is absent in juveniles and females where the anal fin base is straight.

Colour in preservation. Blackish-brown on back, fading into ochre on lower body parts, light ochre on underside, blotches seen in life less distinct in preservation.

Ecology. The Zambezi at Tete is a wide and shallow river with prominent sand islands where people punt their boats (at least in July and August when water flow is low). River banks are not very high. Extensive reed beds offer day-time hiding for a great many mormyrids, and apparently also foraging grounds when active during night (mormyrids identified: Cyphomyrus discorhynchus , Mormyrops anguilloides , Mormyrus longirostris ). There is very little riparian vegetation in the lower reaches of Cahora Bassa Dam and also very few mormyrids. Water conductivity at Cahora Bassa Dam and Tete was rather high for an African river (133–140 MS/cm in July and August 2002 and 2003, at 22–23 u C; Kramer, pers. obs.), but it was even higher by at least one order of magnitude in the delta region, at places considered freshwater sites and at times of the year when water flow was low (mean conductivity of 3150 MS/cm around Marromeu area, July 1999; R. Bills unpubl.). Values reported from the Buzi River were 127 MS/cm at 23.5 u C (early October 2002; R. Bills, pers. comm.)

Distribution. Lower Zambezi River from the delta upstream to at least Tete, if not Victoria Falls; also present in the coastal Pungwe and Buzi systems that are associated with the Zambezi in its south. Marcusenius macrolepidotus is also found in the coastal Mulela system north of the delta. Considered by R. Bills (unpubl.) the most widespread mormyrid in the delta region, with habitats varying from small acidic streams draining the edges of the delta, swamps in the delta, and also the main channel to small pools along the Pungwe–Zambezi divide. Its common presence in the Lower Shire River is confirmed by Tweddle and Willoughby (1982) who also noted more distant records from slow-flowing streams, lagoons and sheltered estuaries of or near Lakes Malawi, Chiuta and Chilwa (the taxonomic identity of these records of M. macrolepidotus needs to be confirmed with regard to the present revision).

Relationships. Considered most closely related to neighbouring species, such as M. altisambesi in the Upper Zambezi River, and also M. pongolensis and M. devosi , due to the confusion of their identities. Also closely related seems to be M. livingstonii (Boulenger 1989) which occurs in parts of the Malawi-Shire system ( Tweddle and Willoughby 1982).

Etymology. Mormyrus macrolepidotus Peters, 1852 , the large-scaled mormyrid, apparently was an exceptionally large-scaled mormyrid when discovered but no longer holds the record in this regard. M. altisambesi and still more so several Marcusenius species from Cameroon are larger-scaled ( Boden et al. 1998).

Figures

Figure 1. All species and forms of the Marcusenius macrolepidotus species complex, as studied in the present paper. (A) M. macrolepidotus (Peters, 1852), ZMB 3678 (lectotype L. Seegers; photo: L. Seegers). (B) Gnathonemus angolensis Boulenger 1905, BMNH 1905.5.29.64 (holotype). (C) Gnathonemus moeruensis Boulenger 1915, MRAC 14137 (holotype). (D) Gnathonemus pongolensis Fowler 1934, ANSP 54950 (holotype). (E) M. macrolepidotus (Peters 1852), SAIAB 060847, coll. R. Bills 1 Aug.1999, Lower Zambezi. (F) M. macrolepidotus (Peters 1852), SAIAB 060947, coll. R. Bills 15 Aug.1999, lower Pungwe River System. (G) M. devosi sp. n., coll. L. de Vos and B. Kramer 3/6 Sept. 2001, Lower Tana River/Kenya. (H) M. macrolepidotus (Peters, 1852), SAIAB 73790 (largest specimen), coll. R. Bills 14 Aug. 2003, Rovuma System. (I) M. macrolepidotus (Peters 1852), SAIAB 055874, coll. R. Bills 20 July 1997, Mulela River/Mozambique. (J) M. altisambesi sp. n., coll. F.H. van der Bank and B. Kramer, 11/12 August 2004, Okavango River, live fish of SL 13 cm photographed 20 April 2006. (K) M. altisambesi sp. nov, coll. F. H. van der Bank and B. Kramer, 21 August 1999, Upper Zambezi, Kalimbeza, live specimen of 16.5 cm SL photographed 3 July 2003. (L) M. macrolepidotus (Peters 1852), sampled together with SAIAB 67369, coll. R. Bills 29 Sept. 2002, Buzi River System, specimen of 13 cm SL photographed alive 22 February 2005. (M) M. pongolensis (Fowler, 1934), resurrected species, specimen of 11 cm SL reared in captivity from parents caught in Crocodile River, Incomati System, in February 1997, photographed alive 15 March 2005.

Figure 4. Partial map of southern Africa showing the sampling localities for Marcusenius sp. Only the larger rivers are shown. Numbers code for origins of samples: (1) Tete on the Lower Zambezi (M. macrolepidotus, as for types); (2) Quanza River (G. angolensis, type; exact sampling site unknown); (3) Lake Mweru (G. moeruensis, type); (4) Pongola River near Paulpietersburg (G. pongolensis, type); (5) Sabie River; (6) Crocodile River; (7) Groot Letaba River (Limpopo System); (8) Blyde River (Limpopo System; (9) KwaMaZulu stream, Mhlatuze System (not shown); (10) Pongola River, more downstream compared to (4); (11) Lisikili, Upper Zambezi; (12) Kwando River, (13) Okavango System; (14) Tana River; (15) Buzi River System; (16) Pungwe River; (17) Lower Zambezi, delta region; (18) Mulela River; (19) Rovuma River System.

Figure 8. Map of sampling locations in South Africa. Numbers explained in Figure 3, except no. (20) which represents two samples from the Nswananzi River: Nkanini stream, KwaZulu-Natal.