Data of fish populations in African freshwaters are scarce and there are no mormyrid species known to be threatened and with extinction and none are CITES-listed. This is not to say that particular species are not under threat of local extinction in areas impacted by human activity, including over-fishing, and development.

Author(s): Sullivan, John P.

Rights holder(s): Sullivan, John P.

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Artificial dichotomous key to 19 genera of Mormyridae  (Heteromormyrus pauciradiatus not included)

1.a. Nostrils close to one another and to the eye; mouth inferior, below the horizontal level of the eye; body short and rather deep; two simple (unsegmented) rays, visible on radiographs, at the origin of the dorsal fin. Petrocephalus (subfamily Petrocephalinae)

1.b. Nostrils separated from each other and from the eye; mouth terminal or inferior, in advance of the level of the eye, body deep or elongate; usually one simple ray at the origin of the dorsal fin. 2 (subfamily Mormyrinae)

2.a. Teeth in both jaws very small, slender and conical, irregularly arranged in several rows forming a villiform band; (additionally snout narrow and tubular, mouth terminal, chin with a tapering barbel-like appendage nearly as long as snout and pointing forwards). Genyomyrus

2.b. Teeth not as above, 3

3.a. Teeth extending along the entire edge of both jaws in a single series, 10-36 in each jaw; (additionally mouth terminal, well in advance of the level of the eye; body elongate, the depth more than 5.2 times into SL). Mormyrops

3.b. Teeth restricted to middle of each jaw, 3-10 in each jaw, 4

4.a. Dorsal fin more than two times the length of anal, originating directly above or in advance of pelvics. Mormyrus

4.b. Dorsal fin 0.10-1.75 times the length of the anal, its origin behind pelvics, 5

5.a. Dorsal fin very short, less than 0.20 times the length of the anal, and set far back on body; (additionally anal fin long with 58-68 rays). Hyperopisus

5.b. Dorsal fin 0.35-1.75 times the length of the anal fin, 6

6.a. Dorsal fin 1.2-1.75 times the length of the anal fin; dorsal fin origin anterior to anal fin origin, 7

6.b. Dorsal fin 0.35-1.1 times length of the anal fin; dorsal fin origin above or posterior to anal fin origin, 9

7.a. Pelvic fins closer to the anal than to the pectorals; body very elongate, at least 8-11 times as long as deep. Isichthys

7.b. Pelvic fins mid-way between anal and pectoral fins or closer to pectorals; body short to moderately elongate, 8

8.a. Symphysial mandibular teeth incisor-like and projecting beyond lower lip; body moderately elongate (depth < 24% SL), upper back gently convex. Myomyrus

8.b. Median pair of mandibular teeth unmodified; body moderately deep (depth >27% SL) and upper back gently to greatly convex. Cyphomyrus

9.a. Posterior nostril close to the border of the mouth. Stomatorhinus

9.b. Neither nostril close to the border of the mouth, 10

10.a. Snout very elongated and tubular, its length greater than the postorbital
length of the head. Snout turned downward. Campylomormyrus

10.b. Snout non-tubular, its length less than the post-orbital length of the head, 11

11. a. Prominent cylindrical barbel-like appendage under the chin, extending forward from below lower jaw. Gnathonemus

11.b. Appendage under chin reduced to fleshy swelling or absent altogether, 12

12. a. Submental appendage present, extending slightly beyond the end of the upper jaw. Marcusenius

12.b. Fleshy chin appendage not extending beyond end of upper jaw or absent altogether, 13

13.a. Dorsal and anal fins approximately equal in length and originating at the same vertical level, dorsal with 31-34 rays, anal with 31-35 rays. Hippopotamyrus (note: H. ansorgii and related forms will not key out here, but with Paramormyrops below)

13.b. Dorsal fin shorter than anal fin and with fewer than 30 rays, 14

14.a. Body moderately elongate, depth 18-22% SL, 15

14.b. Body moderately deep, more than 23% SL, 17

15.a. Anal and dorsal fins terminate at about the same level. Distal tips of last anal and dorsal rays not offset. 16

15.b. Anal fin extends beyond the end of dorsal. Distal tips of last anal and dorsal fin rays offset. Brienomyrus

16.a. Diffuse dark bar between origin of doral and anal fins absent. Paramormyrops 

16.b. Diffuse dark bar between origin of doral and anal fins present. Hippopotamyrus ansorgii complex

17.a. Globular swelling under chin absent; mouth terminal, 18

17.b. Globular swelling under chin present; mouth subterminal, 19

18.a. Snout straight, short and blunt. Brevimyrus

18.b. Snout turned downward, long, cone-shaped. Boulengeromyrus

19.a. Posterior nostril closer to anterior nostril than to eye. Ivindomyrus

19.b. Posterior nostril closer to eye than to anterior nostril. Pollimyrus

Author(s): Sullivan, John P.; Hopkins, Carl D.

Rights holder(s): Sullivan, John P.; Hopkins, Carl D.

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Unlike the electric eel Electrophorus and the electric catfish Malapterurus, mormyrids cannot produce strong electric discharges for defense or to immobilize prey. Instead, by means of a specialized organ near the tail these fishes generate a relatively weak electric field around their body that they monitor using cells embedded in their skin called electroreceptors. Using active electroreception they are able to calculate the size, position and other characteristics of nearby objects in the water and can be active at night when vision is of little use. Electroreception requires a lot of brain power and these fishes have one of the largest brain mass to body mass ratios among vertebrates, roughly equal to that of Homo sapiens. In mormryids it is the cerebellum that has become massively hypertrophied.

Electric organ discharges, or EODs are also used for communication by mormyrids. Mormyrid EODs are pulses between one-tenth of a millesecond to 20 milleseconds in duration. While the time interval between the pulses is variable, the pulse waveform characteristics are fixed and species-specific. EOD waveforms can differ radically among co-occuring mormyrid species and reproductive males will often develop distinctive waveforms that function in courtship of conspecific females. In this way, EODs serve a function analagous to visual or acoustic signals in many other groups of organisms.

Impressive examples of EOD variation among co-occuring species can be found within the genera Paramormyrops of Lower Guinea and Campylomormyrus of the Congo River. The hypothesis that EODs may in fact accelerate speciation in these "riverine species flocks" and within mormyrids generally is another active research area. EODs are relatively easy to record from living mormyrids and because of their species-specificity and stereotypy, are often useful aides in recognizing species boundaries and working out the taxonomy of this group.

Author(s): Sullivan, John P.

Rights holder(s): Sullivan, John P.

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Adult length of mormyrid species ranges from about 4 to about 150 centimeters.

Author(s): Sullivan, John P.

Rights holder(s): Sullivan, John P.

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Mormyrids have a broader distribution than their Nilo-Sudanic sistergroup,Gymnarchus niloticus, including most of the African continent with the exception of the Sahara, northernmost Mahgreb and southernmost Cape provinces (Roberts, 1975) and are most diverse in the river systems of Central and West Africa. 

Author(s): Sullivan, John P.

Rights holder(s): Sullivan, John P.

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Mormyrids occupy an ecological niche largely similar to that of other large group of freshwater weakly electric fishes, the ostariophysan South American gymnotiforms (Lowe-McConnell 1987).  Fishes of both groups, with some exceptions, are nocturnal benthic invertebrate-feeders and have adapted to a number of different types of freshwater habitats. Interestingly, the widely separate phylogenetic positions of these two groups among non-electroreceptive teleost clades indicates independent evolution of their electrosensory systems (see Bass 1986c, Kramer 1990). Mormyrids are much more abundant and diverse in river and stream habitats than in lakes (in marked contrast to the African cichlids).  Some form large schools near the bottom of pools, others are adapted for life in and near rapids (Roberts & Stewart 1976) smaller streams, marginal habitat, or swamps (Lowe-McConnell 1987). Rainy season spawning migrations from river mouths to upriver breeding habitats have been reported for some taxa (Daget 1957, Blake 1977). Little information exists regarding the reproductive behavior in mormyroids, although male Gymnarchus niloticus and Pollimyrus isidori are known to construct and guard elaborate floating nests in which larvae remain for some time after hatching (see Hopkins 1986).

Author(s): Sullivan, John P.

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Recent literature on mormyrid systematics includes Taverne’s taxonomic revision of the family based on osteology (Taverne, 1969; 1971 a; 1971 b; 1972), Bigorne's (1990a) review of the mormyrids of West Africa and revision of Brienomyrus, Pollimyrus, Isichthys and Mormyrops of that region (Bigorne, 1987; 1989; 1990 b), Boden et al.’s (1997) revision of the Marcusenius of Central Africa with eight circumpeduncular scales, Jégu and Lévêque’s (1984) study of Marcusenius of West Africa, and Harder's (2000) published CD-ROM with descriptions and photos of all existing types of specimens of Mormyridae. Despite this recent work, the monophyly of several genera remains poorly supported. 

Most of the foregoing work is not explicitly phylogenetic, and only recent molecular studies have provided a well supported tree for the major mormyrid lineages (Alves-Gomes & Hopkins, 1997, Lavoué et al. 2000, Sullivan et al. 2000, Lavoué et al. 2003).  Points of agreement between the morphological work of Taverne and the molecular studies are 1) the monophyly of Mormyridae, 2) the sistergroup relationship between Mormyridae and Gymnarchus niloticus,  and 3) the basal division of the family into two subfamilies: Mormyrinae and Petrocephalinae, with the latter containing only Petrocephalus.

Another recent development is the use of electric organ discharge (EOD) recordings for species discovery and diagnosis within certain genera (Sullivan et al., 2002; Lavoué et al., 2004). Certain aspects of the EOD appear to be phylogenetically conserved, while others are more variable (Alves-Gomes, 1999; Sullivan & Hopkins, 2001; Sullivan et al., 2000).

Author(s): Sullivan, John P.

Rights holder(s): Sullivan, John P.

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