Gnathonemus petersii (Günther, 1862)
Original Published Description:
Elephantnose fish, Peter's elephantnose, Ubangi mormyrid
Body is moderately deep, about 25-28% SL, with the greatest depth slightly anterior to the origin of the anal fin. The length of the head 20-25% SL, its depth, 66-75% of its length. Dorsal profile convex, descending in a straight line toward the head. Snout, 40% HL. Lower jaw with a cylindrical to tapering dermal appendix which is as long or longer than the snout; teeth small, notched, 3-5 in upper 5-6 in lower. Mouth small and terminal. Nostrils close together, about one eye diameter anterior to forward margin of eye. Eye, small, its diameter about 12% of length of head. Dorsal fin base length about 20-21% SL, with 27-29 rays. Dorsal fin originates above the 10th anal ray. Anal fin base about 27-28 % SL with 34-36 rays. Predorsal distance about 62 % SL; pre-anal distance about 56% SL. Caudal peduncle length about 3.3 times its depth, about 17% SL. 8 circumpeduncular scales. Scales along the lateral line, 63-70. Caudal fin covered with scales, deeply forked. Coloration: black brown with two distinct bands in the shape of parentheses “()” running from origin of dorsal to the origin of the anal fins. The light color of these bands fades in larger specimens.
This is the best-known species of mormyrid due to its popularity in the international aquarium fish trade where it is known as the "elephantnose fish."
Electric Organ Discharge
In the laboratory, EODs of G. petersii are often sexually dimorphic, with the male EOD longer in duration than that of the female. The EOD has three phases: an initial head negative phase which is visible only after amplifying the vertical axis of the display, followed by a head-positive then head-negative phase. The duration of the EOD is approximately 300 to 500 µs. The presence of an initial head-negative phase to the waveform is characteristic of an electric organ with electrocytes which have penetrating stalks.
Maximum size: 350 mm SL.
Ecology and Distribution
Among the most widespread mormyrid species. Such a large distribution suggests revisionary work may uncover multiple species. In Lower Guinea found in the Cross, Mungo, Wouri, Lokoundjé, and Lower Sanaga Rivers. Elsewhere widely distributed throughout central Africa from the Niger Delta to the Congo River basin. The holotype is from Old Calabar, at the mouth of the Calabar and Cross Rivers. See FishBase for museum records and localities.
small to large rivers
- Gnathonemus brevicaudatus Pellegrin, 1919 (synonym (subjective = heterotypic))
- Mormyrus petersii Günther, 1862 (synonym)
- Gnathonemus histrio Fowler, 1936 (synonym (subjective = heterotypic))
Holotype (unique): BMNH 18188.8.131.52
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