Petrocephalus magnoculis, 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 : 2241-2242

Petrocephalus magnoculis sp. nov.

( Figure 2, no. 23; online Figure 8 )

Type specimens. Holotype: SAIAB 78788 (specimen Ruac06) from Cunene River, just below Ruacana Falls . Paratypes: SAIAB 186053 (specimen Ruac09) , SAIAB 79480 (specimen Ruac10) , SAIAB 78790 (specimen Ruac17) , ZSM 38659 (specimen Ruac07) , ZSM 38660 (specimen Ruac13) .

Type locality. Namibia: Cunene River : just below the Ruacana Falls, Hippo Pool Campsite, 17 ◦ 24 ′ 24 ′′ S, 14 ◦ 13 ′ 01 ′′ E, about 800 m altitude .

Diagnosis. Eye diameter defined by orbital rims, OD, mean 0.294 (range 0.259 –0.329) of HL, head length; number of scales in lateral line row, SLS, median 40 (range 38–42); length of snout to posterior orbital rim of eye, LSo, mean 0.485 (range 0.47–0.514) of HL, head length; length of snout to centre of eye, LSc, mean 0.37 (range 0.352 –0.391) of HL; head length, HL, mean 0.258 (range 0.25–0.277) of SL; preanal length, PAL, mean 0.611 (range 0.59–0.628) of SL; anal fin length, LA, mean 0.234 (range 0.215 –0.256) of SL; number of dorsal fin rays, nD, median 23 (range 20–24); body depth, BD, mean 0.312 (range (0.283–0.34) of SL; distance between the pair of nares of one side, Na, mean 27.9 (range 24.3–31.1) times in HL, head length.

Description. Body oval shape ( Figure 2, no. 23). Head with rounded nose, 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 20 (n = 1), 21 (n = 0), 22 (n = 2), 23 (n = 2), 24 (n = 4). 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 = 0), 28 (n = 2), 29 (n = 2), 30 (n = 3), 31 (n = 1). 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, 38 (n = 1), 39 (n = 1), 40 (n = 2), 42 (n = 1). Scales on caudal peduncle circumference, 11 (n = 1), 12 (n = 7), 13 (n = 1). Caudal peduncle slender, subcylindrical entire length, usually 19.9% (18.4–21.8%) of SL ( Table 1). Electric organ discharge a triphasic pulse with strong head-positive phase P1 followed by head-negative main phase N, and head-positive P2 phase of 30% amplitude re: P1 phase ( Figure 10 ). Pulse duration mean 443 (394–536) µs (n = 4); 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 beige, back darker and grey, but brown where mormyrid skin gone.

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

Ecology. The Cunene River is dammed for hydroelectric power generation just above Ruacana Falls in Angola. Even in the dry season when the Falls proper were completely dry the water level just below the Falls was regulated rather high, and the current rather strong. Dicotyledonous trees, extensive reed beds and semiaquatic bushes dominated the river banks. River banks were rocky or sandy, depending on whether they were on the inside or outside bank. Crocodiles were seen, and hippopotamus are reported for the area but were not seen. At 800 m sea level marked diurnal temperature differences with chilling nights. Online Figure 9.

Distribution. Presently known only from just below the Ruacana Falls; downstream limit perhaps at Epupa Falls. Nothing is known about whether P. magnoculis sp. nov. is also found upstream of Ruacana Falls.

Etymology. Species name derived from magnus, great, and oculus, eye.

Remarks. In P. magnoculis sp. nov., Eye diameter and SLS are in the top range compared with the other species, also LSo, LSc, HL and PAL, whereas LA is in the lower range.

Figures

Figure 8. Principal component analysis on 17 anatomical characters (see Table 1), for six Okavango samples, focusing on that of the Boro River (Petrocephalus magnitrunci sp. nov., red triangles). (A) Boro/Xakanixa River (blue squares); (B) Boro/Gadikwe Lagoon (blue squares); (C) Boro/Xakanixa Channel (blue squares); (D) Boro/Popa Rapids (blue squares); (E) Boro/Upper Zambezi River (blue squares); (F) Boro/Cunene River (blue squares). The 17 characters included in the analysis were: PDL/SL, PAL/SL, LD/SL, LA/SL, pD/SL, CPL/SL, CPD/CPL, Lso/HL, HL/SL, BD/SL, nD, nA, SPc, SLS, OD/HL, LPF/HL, PPF/SL. Characters of Table 1 that were excluded: HL/Na, LSc/HL.

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.