Pollimyrus cuandoensis, Kramer & Bank & Wink, 2013

Kramer, Bernd, Bank, Herman van der & Wink, Michael, 2013, Marked differentiation in a new species of dwarf stonebasher, Pollimyrus cuandoensis sp. nov. (Mormyridae: Teleostei), from a contact zone with two sibling species of the Okavango and Zambezi rivers, Journal of Natural History (J. Nat. Hist.) 48 (7 - 8), pp. 429-463 : 445-447

Pollimyrus cuandoensis sp. nov.

( Figure 1K, L )

Type specimens. Holotype: ZSM 41805, field no. Kon 26G, 50 mm SL (live), from Kwando River at Kongola Bridge, 17 ◦ 47 ′ 33 ′′ S, 23 ◦ 20 ′ 33 ′′ E, 25 August 1999, water conductivity and temperature, 236 µS cm−1 and 19 ◦ C . Paratypes: ZSM 39522, same date and place, specimens Kon02G, Kon16G, Kon17G, Kon18G, Kon19G, Kon21G, Kon22G, Kon23G, Kon25G, Kon27G, Kon28G, Kon29G, Kon30G, Kon31G, Kon39G, Kon40G, size range 32–60 mm SL (measured alive) .

Nontypes: From Nkasa Island, 18 ◦ 26.5 ′ S, 23 ◦ 38 ′ E: ZSM 39515, specimens 1Fish, 2Fish, 7 Sept. 1993 ; ZSM 39516, specimens 3Fish, 6Fish, 8 Sept. 1993 ; ZSM 39517, specimen 10Fish ; ZSM 39518, specimens 12Fish, 13Fish; size range 33–60 mm .

From Nakatwa, 18 ◦ 06 ′ S, 23 ◦ 23 ′ E: ZSM 39519 (6), specimens N56ka, N57ka, N58ka, N59ka, N62ka, N63ka, 9 March 1994 ; ZSM 39520 (12), specimens N64ka, N66ka, N67ka, N68ka, N69ka, N70ka, N71ka, N74ka, N76ka, N77ka, N78ka, N79ka, 10 March 1994 ; ZSM 39521 (3), specimens N81ka, N96ka, N97ka, 11 March 1994 ; size range 24–56 mm.

From Kongola Bridge, 17 ◦ 47 ′ 33 ′′ S, 23 ◦ 20 ′ 33 ′′ E: ZSM 39523, specimens Kon01G, Kon18G ∗, 24 January 2001, size range 48–58 mm SL ; ZSM 41773, K89–K92, K97– K112 (20 specimens), 8 August 2004, size range 2.3–3.9 cm .

From Sampis , Linyanti River, 18 ◦ 04 ′ 59.6 ′′ S, 24 ◦ 02 ′ 7 ′′ E: ZSM 39532 (14), specimens Lin01–Lin14, 9 September 1997 ; ZSM 39533 (15), specimens Lin15–Lin28, and “without no.”, 10 September 1997 ; size range 35–65 mm SL.

Type locality. Kwando (Cuando) River at Kongola Bridge, 17 ◦ 47 ′ 33 ′′ S, 23 ◦ 20 ′ 33 ′′ E .

Diagnosis

SPc, median = 14 (range 12–16; N = 19); PDL, mean = 0.6516 of SL (range 0.6333 –0.6852; N = 19); LD, mean = 0.1636 of SL (range 0.14–0.1818); LA, mean = 0.216 of SL (range 0.18–0.2417); PPF, mean = 0.1696 of SL (range 0.1507 –0.1873); CPL, mean = 0.2181 of SL (range 0.1898–0.24); CPD, mean = 0.3474 of CPL (range 0.3214 –0.4146); LSo, mean = 0.4517 of HL (range 0.4059–0.5); BD, mean = 0.2753 of SL (range 0.2467 –0.3051); nD, median = 17 (range 15–18); nA, median = 23 (range 21–24); SLS, median = 50 (range 44–55); PAL, mean = 0.6014 of SL (range 0.5849 –0.6343); LPF, mean = 0.8319 of HL (range 0.7639 –0.9257); pD, mean = 0.395 of SL (range 0.3796 –0.426); OD, mean = 0.2635 of HL (range 0.2376 –0.3050); HL, mean = 0.2422 of SL (range 0.2255 –0.2633); Na, contained in HL, mean = 9.02 (range 8.31–9.92). Electric organ discharge, EOD, with five phases and last phase P2 not stronger than P1. (See Remarks) .

Description

Body oblong shape. Head broadly rounded with a small, terminal mouth; head and body dorsoventrally compressed. Dorsal fin (a) origin situated about two thirds of standard length from snout, (b) obliquely orientated, anteriorly higher and posteriorly lower, (c) first few rays anteriorly longer than those posteriorly, and (d) median number of rays 17 (15–18). Anal fin (a) opposite dorsal but origin more anteriorly and also obliquely orientated, (b) anteriorly lower and posteriorly higher, in male specimens anterior 10 or so rays longer than those posteriorly, (d) margin broadly rounded, (e) and median number of rays 23 (21–24). Scales (a) cycloid with reticulate striae, except in centre, extending anteriorly to operculum, pectoral and pelvic fins. SPc, median = 14 (12–16). Caudal peduncle slender and subcylindrical over the entire length, usually less than a quarter in standard length, SL. Forked tail fin with broadly rounded lobes overlapping at midbase. Electric organ discharge with five phases and of short duration, a mean 0.5 ms (range 0.34–0.64 ms) at 25 ◦ C and “5% amplitude-of-N1-phase criterion” (see Material and methods).

Colour in preservation. Mottled brown, throat and belly light beige covered with small brown spots.

Colour in life. Similar to preserved specimens.

Ecology. Prefers to hide in weeds if present, floating or not, often high up in water column, sometimes even at the surface under a water lily leaf in bright sunlight. Also found on rocky bottom, hiding in crevices and holes; will do so also in aquarium during the day where there is no predation pressure. Will often not struggle in weeds brought to shore, so as not to raise attention. Appears not to be a strong swimmer, in contrast to the Petrocephalus species of southern Africa that are only somewhat bigger.

Distribution

At present known only from the lower section of the Kwando (Cuando) River, Caprivi Strip, Namibia.

Remarks

The most useful (quickest) character to distinguish between P. castelnaui , P. marianne and P. cuandoensis sp. nov. is the electric organ discharge, EOD, which is characteristically different in the three species. P. cuandoensis sp. nov. can be recognized by its median number of scales around the caudal peduncle which is usually 14 rather than 12 in P. castelnaui and 16 in P. marianne . P. cuandoensis sp. nov. is also distinguished from P. castelnaui by a combination of morphological characters, such as lower scores for PDL, PPF, CPD, LSo, OD, and BD in the latter. From P. marianne , P. cuandoensis sp. nov. is distinguished by higher scores for PPF, CPD, LSo, OD, BD and nD, lower scores for LA and SLS in the latter.

Etymology

The species name cuandoensis refers to the Kwando (Cuando) River that passes through the Caprivi Strip, Namibia.

Figures

Figure 1. Partial map of Upper Zambezi system and Okavango delta geography. Localities where Pollimyrus specimens were sampled indicated as: Z1, Zambezi: Katima Mulilo; Z2, Zambezi: Lisikili; L, Kwando system: Linyanti: Sampis; “&” symbol, Kwando system: Nkasa Island; N, Kwando: Nakatwa; K, Kwando: Kongola Bridge; O1, Okavango: Guma Lagoon; O2, Okavango: Makwena.