Petrocephalus catostoma
Creators: name: Kramer, Bernd
name: Bills, Roger
name: Skelton, Paul
name: Wink, Michael
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Osteoglossiformes
Mormyridae
Petrocephalus
Petrocephalus catostoma

description: Petrocephalus catostoma (Günther, 1866)   
(Figure 2, nos 1, 28; online Figure 1)  
 Mormyrus catostoma Günther, 1866: 222.   
 Petrocephalus catostoma: Boulenger 1898: 790.   
 Petrocephalus catostoma catostoma: Whitehead and Greenwood 1959: 284.   
 Type specimens. BMNH 1863.10.12.4 (lectotype) and four paralectotypes BMNH 1863.10.12.5-6 (4) (studied)   
 Type locality. Rovuma (Ruvuma) River, Tanzania / Mozambique (lower reaches, place unspecified).   
 Diagnosis. Preanal length, PAL, mean 0.625 (range 0.602 –0.656) of SL; length of snout to posterior orbital rim of eye, LSo, mean 0.423 (range 0.398 –0.454) of head length, HL; head length, HL, mean 17.43 (range 16.07–23.21) times Na, distance between the pair of nares of one side; body depth, BD, mean 0.274 (range 0.252 –0.306) of SL; number of dorsal fin rays, nD, median 20 (range 18–22); number of anal fin rays, nA, median 27 (range 25–29); head length, HL, mean 0.277 (range 0.249 –0.291) of SL; number of scales around caudal peduncle, SPc, median 14 (range 12–16).   
 Description. Body oval shape (Figure 2, nos 1 and 28). 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 18 (n = 1), 19 (n = 8), 20 (n = 17), 21 (n = 8), 22 (n = 1). 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 25 (n = 3), 26 (n = 14), 27 (n = 15), 28 (n = 3). Forked tail fin with rounded lobes. Scales cycloid with reticulate striae, scales extending anteriorly to operculum and pectoral fins (beyond pelvics). Scales on caudal peduncle circumference, 11 (n = 1), 14 (n = 25), 16 (n = 9). Caudal peduncle slender, subcylindrical entire length, usually 21% (19.5–23.85%) of SL (Table 1). 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, back darker, underside fair.   
 Colour in life. Grey-silver, underside lighter, paired fins light and transparent, goldbrownish hue on back and tail section.   
 Ecology. The species is common and widespread throughout upper catchments within the Niassa Reserve. Occurs in aquatic weed beds, marginal vegetation and root-stocks of bank vegetation in headwater streams through to floodplain margins. Water conductivities ranging from 104 to 268 µS / cm in August 2003, probably reflecting human impact (Bills 2004; personal observation). Online Figures 2–5.   
 Distribution. Rovuma System including Niassa Reserve (no. 28 on Figure 1), also western confluences to Lake Malawi (nos 16–18), but probably not Lake Chiuta (no. 19).   
 Remarks. Compared with the other species, P. catostoma is distinguished by its very low range for PAL, LSo, HL / Na, BD, nD, nA, but long HL, and an SPc median of 14 intermediate between the extremes.   
 Petrocephalus congicus David and Poll, 1937 (resurrected and elevated to species rank)   
(Figure 2, no. 26)  
 Petrocephalus stuhlmanni congicus David and Poll, 1937: 199. Whitehead and Greenwood 1959: 286 (synonymy with Petrocephalus catostoma congicus).   
 Type specimens. Syntypes: MRAC 30807-30808 (2) (studied)   
 Type locality. Mukishi River at Lumami, Congo River basin, Democratic Republic of Congo (08 ◦ 30 ′ S, 24 ◦ 44 ′ E).   
 Diagnosis. Predorsal length, PDL, mean 0.627 (range 0.618 –0.635) of SL; preanal length, PAL, mean 0.556 (range 0.535 –0.578) of SL; dorsal fin length, LD, mean 0.16 (range 0.155 –0.166) of SL; anal fin length, LA, mean 0.237 (range 0.234 –0.241) of SL; distance dorsal fin origin to end of caudal peduncle, pD, mean 0.427 (range 0.417 –0.438) of SL; length of caudal peduncle, CPL, mean 0.232 (range 0.228 –0.237) of SL; depth of caudal peduncle, CPD, mean 0.2965 (range 0.296 –0.297) of CPL, length of caudal peduncle; length of snout to centre of eye, LSc, mean 0.334 (range 0.326 –0.343) of HL; length of snout to posterior orbital rim of eye, LSo, mean 0.419 (range 0.408 –0.429) of HL; head length, HL, mean 0.234 (range 0.231 –0.238) of SL; distance between the pair of nares of one side, Na, mean 20.1 (range 18.87–21.32) times in HL, head length; body depth, BD, mean 0.293 (range 0.286–0.3) of SL; dorsal fin ray number, nD, median 18.5 (range 18–19); anal fin ray number, nA, median 27.5 (range 27–28); number of scales around caudal peduncle, SPc, median 12 (range, 12–12).   
 Remarks. “Judging from the known range of variation within P. c. catostoma it seems possible that the two Congoan forms [i.e. haullevillii and congicus] may yet have to be united” (Whitehead and Greenwood 1959: 286). Petrocephalus stuhlmanni congicus is distinguished from other Petrocephalus by one of the shortest values for head length, HL, in combination with dorsal fin ray number, nD, in the lowest range. This leaves only P. haullevillii as an alternative. Petrocephalus stuhlmanni congicus differs from P. haullevillii by a rosette of electroreceptor organs (above the eye, Augenrosette; Harder 1968), absent in P. haullevillii that has no such rosette (S. Lavoué, personal communication). Among other differences, P. congicus and P. stuhlmanni differ markedly in their values for caudal peduncle depth (CPD) and head length (HL); these characters are among the greatest in the former and smallest in the latter species in the present assemblage of Petrocephalus.
description: Published as part of 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, pp. 2179-2258 in Journal of Natural History 46 (35 - 36) on pages 2233-2235, DOI: 10.1080/00222933.2012.708452, http://zenodo.org/record/4590828