Petrocephalus longicapitis, Kramer & Bills & Skelton & Wink, 2012

Kramer, Bernd, Bills, Roger, Skelton, Paul & Wink, Michael, 2012, A critical revision of the churchill snoutfish, genus Petrocephalus Marcusen, 1854 (Actinopterygii: Teleostei: Mormyridae), from southern and eastern Africa, with the recognition of Petrocephalus tanensis, and the description of five new species, Journal of Natural History 46 (35 - 36), pp. 2179-2258 : 2238-2239

Petrocephalus longicapitis sp. nov.

( Figure 2, no. 7; online Figure 7 )

Type specimens. Holotype: SAIAB 85916 (specimen 19fish) from Upper Zambezi River at Katima Mulilo, East Caprivi, Namibia . Paratypes: SMF 28265 (27 specimens), plus SAIAB 85917 (specimens 14fish, 16fish) , SAIAB 85911 (25fish, 26fish) , SAIAB 85918 (37fish, 38fish, 43fish) .

Type locality. Upper Zambezi River at Katima Mulilo, East Caprivi, Namibia, approx. 17 ◦ 29 ′ 30 ′′ S, 24 ◦ 16 ′ 18 ′′ E .

Diagnosis. Head length, HL, mean 0.279 (range 0.258 –0.296) of SL; predorsal length, PDL, mean 0.635 (range 0.619 –0.657) of SL; preanal length, PAL, mean 0.596 (range 0.575 –0.617) of SL; depth of caudal peduncle, CPD, mean 0.36 (range 0.334 –0.398) of CPL, length of caudal peduncle; number of scales around caudal peduncle, SPc, median 12 (range 12–12); eye diameter as defined by orbital rims, OD, mean 0.261 (range 0.249 –0.281) of HL, head length; body depth, BD, mean 0.295 (range 0.277 –0.315) of SL; length of anal fin, LA, mean 0.237 (range 0.221 –0.252) of SL; length of snout to posterior orbital rim of eye, LSo, mean 0.431 (range 0.389 –0.458) of HL, head length; number of dorsal fin rays, nD, median 23 (range 21–25); number of scales in lateral line row, SLS, median 38 (range 37–39). EOD characteristics at 25 ◦ C and “2% threshold criterion” (see Material and methods): peak amplitude of P2 phase, P2amp, in males, mean 0.466 (range 0.321 –0.547) of P1amp, peak amplitude of P1 phase; in females, mean 0.382 (range 0.206 –0.517) of P1amp; duration of P2 phase, P2dur, mean 207 µs (range 113–477 µs); duration of P1 phase, P1dur, mean 131 µs (range 101–169 µs); duration of N phase, Ndur, mean 49 µs (range (36–62 µs); negative peak amplitude (absolute value) of N phase, Namp, mean – 2.77 (range – 2.291 to –3.468) of P1amp, peak amplitude of P1 phase.

Description. Body oval shape ( Figure 2, no. 7). Head broadly rounded with a small ventrally positioned subterminal mouth, situated ventral to the eye; head and body dorsolaterally compressed. Dorsal fin (a) origin situated about two-thirds of standard length from snout, (b) obliquely orientated, anteriorly higher and posteriorly lower, (c) distal margin crescentic with anterior two or three rays longer than posterior rays, and (d) number of rays 21 (n = 2), 22 (n = 10), 23 (n = 21), 24 (n = 3), 25 (n = 2). Anal fin (a) longer than dorsal fin, (b) opposite dorsal fin with slightly more anterior origin, (c) obliquely orientated, anteriorly lower and posteriorly higher, (d) anterior 10 or so rays longer than posterior ones, especially in males where they also appear stronger, (e) margin broadly rounded, (f) rays posterior to first 10 with distal margin straight, (g) number of rays 26 (n = 1), 27 (n = 1), 28 (n = 23), 29 (n = 11), 30 (n = 2). Forked tail fin with rounded lobes. Scales cycloid with reticulate striae, scales extending anteriorly to operculum and pectoral fins (beyond pelvics). Scales in lateral series, 37 (n = 3), 38 (n = 8), 39 (n = 1). Scales on caudal peduncle circumference, 12 (n = 38). Caudal peduncle slender, subcylindrical entire length, usually 19.9% (18–21.5%) of SL ( Table 1). Electric organ discharge, triphasic pulse with strong head-positive phase P1 followed by head-negative main phase N, and weaker head-positive P2 phase ( Figure 10 ); P2 phase stronger in males than in females of same size. Pulse duration short [mean 379 µs (range 298–642) in females (n = 19) and 354 µs (253–473) in males (n = 15), respectively; 25 ◦ C, 2% threshold criterion]. Males with kink in anal fin base, which is absent in juveniles and females where the anal fin base is straight.

Colour in preservation. Light brown.

Colour in life. Colour in life: grey-silver, underside lighter, paired fins light and transparent.

Ecology. Appears to prefer quiet reaches of oxbow lakes or arms with dense vegetation on borders. Both sexes are territorial during the day but combine to schools at night ( Scheffel and Kramer 2006). Van der Waal and Skelton (1984) studied the fishes of Caprivi, and found P. longicapitis sp. nov. to be abundant in the Zambezi River and common in the Eastern Floodplain, in the Chobe and in Lake Liambezi (which has since dried up), but rare in the Kwando River. The species was common in the shallow water of swamps and flood plains, but rare in streams with sandy or rocky substrate, and also rare in pools beneath Salvinia molesta mats. Where it occurs in the main river channel, sand and gravel substrate mainly with occasional rocky rapids. Marginal roots stocks of riparian trees and patches of aquatic vegetation beds. During the day P. longicapitis sp. nov. is associated with marginal cover in holes in banks, root stocks and aquatic weed beds.

Distribution. Presently known only from the lower and the upper reaches of the Upper Zambezi River: East Caprivi, Namibia, and Lumwana River, Zambia.

Etymology. The species name longicapitis sp. nov. refers to this species’ long head (longus, long and caput, head).

Remarks. Petrocephalus longicapitis sp. nov. is characterized by a long HL, PDL, PAL, CPD and low SPc. The EOD shows a strong P2 phase of short duration, short P1dur, short Ndur, and weaker Namp than P. tanensis .

Figures

Figure 7(A–E). Principal component analysis on the 13 anatomical characters of Table 3, for six Okavango populations, focusing on the Guma Lagoon sample (Petrocephalus okavangensis sp. nov., red triangles). (A) Guma/Popa Falls (blue squares). (B) Guma/Gadikwe (blue squares). (C) Guma/Xakanixa Channel (blue squares). (D) Guma/Xakanixa River (blue squares). (E) Guma/Boro River (blue squares). (F) Popa Falls (red triangles)/Boro River (blue squares).

Figure 10. Differentiation within Petrocephalus wesselsi of different South African origins, studied using Principal Component (PCA) and Discriminant (DA) Analyses, as compared with another species (P. longicapitis sp. nov., Namibia, Upper Zambezi). Circles in DA, 95% confidence circles to contain true mean of group. (A) PCA and (B) DA on correlations among anatomical characters. (C) PCA and (D) DA same as (A) and (B), respectively, but for analyses on characters of Electric Organ Discharges (EODs). Green M symbols, specimens from Mokolo (Mogol) River (n = 48; 43, i.e. 48 for anatomy and 43 for EOD); blue-green N symbols, Nwanedzi River (n = 9; 0); orange B symbols, Blyde River (n = 5; 5); red S symbols, Sabie River (n = 44; 39); blue Z symbols, P. longicapitis sp. nov. from the Upper Zambezi (type locality Katima Mulilo; n = 38; 42); bluer shade of blue-green coloured U symbols, specimens from Mbuluzi River, Swaziland (n = 4; 0). Excluded from DA but shown on DA graphs: lilac G symbols, Groot Letaba River (n = 2; 2); sand-coloured L symbols, Lepalala River (n = 2;1); redder shade of lilac P symbol, Pongola River (n = 1; 1). The 15 anatomical characters included in the anatomical analyses were: PDL/SL, PAL/SL, LD/SL, LA/SL, pD/SL, CPL/SL, CPD/CPL, LSc/HL, LSo/HL, HL/Na, HL/SL, BD/SL, nD, nA, SPc. The characters used in the EOD analyses were: Namp, P2amp, P1dur, Ndur, P2dur, P1Nsep, P1P2sep, NP2sep, P1area, Narea, P2 area.