Description of Mormyrops deliciosus (here regarded as synonym of M. anguilloides) from Boulenger 1909, pp. 32-34:
Depth of body 5½ to 6½ times in total length, length of head 3½ to 4½ times. Head nearly twice as long as deep, upper profile slightly concave; snout rounded; jaws equal; width of mouth nearly equal to length of snout; teeth truncate or conical in the adult, more or less distinctly notched in the young, 24 to 36 in each jaw; eye small, in anterior third of the head, its diameter 2 (young) to 4 times in length of snout or in interocular width. Dorsal 21-27, ½ to 2/3 length of anal, originating 2 to 2 ½ times as far from end of snout as from base of caudal. Anal 40–51, originating considerably in advance of dorsal (its 12th to 16th ray corresponding to the first dorsal ray), and a little nearer head than root of caudal. Pectoral rounded, 2/5 to 1/2 length of head, ventral 1/4 to 1/3. Caudal rather small, densely scaled, with rounded lobes. Caudal peduncle 2 to 2½ times as long as deep, 1/3 to ½ length of head. 85-100 scales in lateral line, 15-18 / 18-22 in transverse series on body, 22-26 in transverse series between dorsal and anal, 14-18 round caudal peduncle. Brownish or olive above, silvery beneath.
Central Africa: Mormyrops anguilloides is known from throughout the Congo River basin. Elsewhere, it is known from the Lower Guinea region, distributed in the Sanaga River basin, in the Nyong, the Lokoundjé and the Cross.
Eastern Africa: It is known from the Lake Albert basin, and Albert Nile, as well as from the Malagarasi River and Lake Tanganyika. It is also known from Lake Malawi. In Kenya it has been recorded from the Northern Ewaso Nyiro system (Seegers et al. 2004) but this is probably not correct. An uncertain record of M. anguilloides from the Athi River basin discussed by Okeyo (1998) is unsubstantiated (Seegers et al. 2004).
Northeast Africa: This species is present in the Ghazal and Jebel systems, White Nile, and the Blue Nile to Lake Nasser (also known as Lake Nubia). It also occurs in the Wabi Shebelle basin, Ethiopia.
Southern Africa: In southern Africa it is restricted to the middle and lower Zambezi and the Buzi and Pungwe Rivers (Skelton 2001).
Western Africa: M. anguilloides has a very wide distribution area and is present in the most parts of West African basins.
Widespread: Senegal, Gambia, Nile, Niger, Lake Chad, Congo Basin and Zambezi, Lake Malawi.
to 1.5 meters SL.
Zambezi River Demersal Habitat
This taxon is one of a number of demersal species in the Zambezi River system of southern Africa. Demersal river fish are found at the river bottom, feeding on benthos and zooplankton
Nutrient levels in the Zambezi River are relatively low, especially in the upper Zambezi; in that reach, above Victoria Falls, most of the catchment drains Kalahari sands, whose nutrient levels are inherently low due to their aeolian formation; moreover, agricultural fertilizer addition throughout the Zambezi watershed is low, due to the shortage of capital available to farmers of this region.
Nitrate levels (as nitrogen) in the upper Zambezi are typically in the range of .01 to .03 milligrams per liter. Correspondingly electrical conductivity of the upper Zambezi is on the order of 75 micro-S per centimeter, due to the paucity of ion content. From the Luangwa River downstream nitrate levels elevate to .10 to .18 milligrams per liter, and electrical conductivity rises to a range of two to four times the upper Zambezi levels. Not surprisingly, pH, calcium ion concentration, bicarbonate and electrical conductivity are all higher in portions of the catchment where limestone soils predominate compared to granite.
There are a total of 190 fish species present in the Zambezi River, including eel and shark taxa. The largest native demersal species present are the 117 centimeter (cm) long tiger fish (Hydrocynus vittatus), the 175 cm African mottled eel (Anguilla bengalensis labiata), the 120 cm Indonesian shortfin eel (Anguilla bicolor bicolor), the 200 cm Giant mottled eel (Anguilla marmorata), the 150 cm African longfin eel (Anguilla mossambica), the 183 cm Sampa (Heterobranchus longifilis), the 150 cm Cornish jack (Mormyrops anguilloides) and the 700 cm largetooth sawfish (Pristis microdon).
Habitat and Ecology
Evolution and Systematics
Phylogenetic study of the widely distributed populations of M. anguilloides is needed to examine monophyly of this species as its currently defined.
Molecular Biology and Genetics
Barcode data: Mormyrops anguilloides
No available public DNA sequences.
Download FASTA File
Statistics of barcoding coverage: Mormyrops anguilloides
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
Relevance to Humans and Ecosystems
The Cornish jack, Mormyrops anguilloides, is a species of weakly electric fish in the family Mormyridae, native to quiet waters in much of Sub-Saharan Africa. The largest species in its family, the Cornish jack is a nocturnal group hunter of smaller fishes, using electricity to locate its prey and communicate with other members of its group. It is a commercial game fish valued for its size and taste.
The common name "Cornish jack" likely originated from European settlers, who thought that this fish resembled the European pike, whose young is known as a "jack" in some parts of England. It is also known as "African carp", a name that is used for several other species.
Distribution and habitat
The Cornish jack occurs in the White Nile, the Lake Albert drainage basin, inland waters from Senegal to Chad, rivers in Cameroon, and small coastal basins in the Guinean zone. It is also widespread in the Congo River basin, Lakes Malawi and Tanganyika, the Volta River basin, the Shebelle River, and the Jubba River. In southern Africa, it is restricted to the middle and lower Zambezi, and the Buzi and Pungwe Rivers.
This demersal species is found in tropical freshwater habitats between 22 and 24 °C (72 and 75 °F). The juveniles are found in marginal habitats, while the adults prefer deep, quiet water between boulders and below overhangs, away from strong currents. They also occur beneath Salvinia mats and in river estuaries in Lake Kariba.
The body and head of the Cornish jack are elongated; the head is nearly twice as long as high, smooth and depressed in front. The snout is rounded and almost as wide as the head. The mouth is terminal, with the upper jaw slightly longer than the lower, both bearing a single row of small, pointed teeth. The eyes are very small and placed in the front third of the head. The gill openings are small and inclined at an angle. The dorsal and anal fins are set well back on the body; the caudal fin is relatively small and forked with rounded lobes. There are 21–30 fin rays in the dorsal and 38–51 rays in the anal fin. The anal fin of the male differs from that of the female in having longer rays and a pronounced concavity in the anterior half.
The scales are small, numbering 85–100 in the lateral line. The coloration is gray above, lighter silvery white below, often with a bronze or yellow sheen. The juveniles are darker in color, being grayish blue or brown. The meristic characteristics of the body (such as the number of scales, fin rays, and vertebrae) vary by geographic location. The largest members of the family Mormyridae, Cornish jacks attain a maximum known length of 1.5 m and a weight of 15 kg.
Biology and ecology
Like other mormyrids, Cornish jacks have an electric organ and generate weak pulses of electricity for navigation, finding food, and communication. Electroceptive cells allow it to detect distortions in the electric field surrounding its body, and determine the size, distance, and properties of the causative object.
Adult Cornish jack are primarily piscivorous; along the Bia River, fish in lake environments feed mainly on tilapia (Sarotherodon and Tilapia) with significant seasonal variation in diet, whereas fish in river environments take both fish and crustaceans. The juveniles feed mostly on shrimps and aquatic insect larvae; larger individuals about 17 cm long also take small cichlids, minnows, and labeos. Historically, Cornish jacks have been thought to feed on decomposing matter, as they were known to congregate around human encampments where large amounts of refuse was dumped into the water.
Observations of Cornish jacks in Lake Malawi show that they form relatively stable groups of 2 to 10 individuals. During the day, the group shelters together in caves, and at night they hunt for cichlids together over rocky reefs to a distance of 20 m (66 ft) from their shelter. Occasionally individual fish will temporarily separate from the others after capturing a cichlid. When a potential prey item is detected, the fish will approach to within 1–20 cm (0.39–7.87 in) before stopping and producing regular pulses of electricity at 20–40 millisecond (ms) intervals. This "stationary probing" behavior could allow the Cornish jack to estimate prey size, as they preferentially target smaller cichlids. After a few seconds, a strike may follow, during which the rate of electrical pulses generated may increase to once every 18–20 ms. In many cases, the targeted cichlid showed little movement prior to capture, indicating that they were unaware of the predator's presence.
Group-hunting Cornish jacks capture more prey and make more successful attacks than those hunting alone. However, it is yet unclear what exact advantages are conferred by the group, as the prey items are not shared between individuals and often individuals steal prey from each other. One possibility is that feeding efficiency is increased by multiple predators making strikes on the same prey fish within a short time of each other.
Differences in the waveforms of their electrical pulses may allow Cornish jacks to recognize each other individually, and thus maintain the identity of their groups. Cornish jacks in groups will adjust the rate of their electrical pulses so that they occur at 18–20 ms delays relative to each other; this "echo response", common in mormyrids, is especially robust in Cornish jacks and serves to minimize electrical interference between different individuals. Cornish jack hunting groups have also been recorded producing synchronized bursts of electrical pulses lasting 1–2.5 s every few minutes. These bursts have been proposed to be mutual group recognition signals.
The Cornish jack is oviparous and spawns in summer during the rainy season. In the upper Ogun River, Cornish jacks and other piscivorous fishes are especially abundant at the beginning and middle of the annual flood, suggesting that they migrate upstream to breed and retreat downstream when the water recedes. The females are fractional spawners and may carry 25,000 or more eggs. In the Baoulé River, this species attains maturity at no less than 34.6 cm (13.6 in) long. Their lifespan may be eight or more years.
Relationship to humans
The Cornish jack is a popular species for anglers and is also taken by spearfishermen. Due to their relatively small mouths, the bait used can be a thin filet of fish, worms, or crabs, and they can be taken by light tackle as they are not known for their fighting abilities. The flesh is held in high esteem; the species name of one of its synonyms, Mormyrops deliciosus, reflects this fact. Theodore Gill (1902) noted that it was fished for mostly at dawn and sunset, and that a 5-foot (1.5 m) fish might fetch a price of 25 francs at Boma.
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- Froese, Rainer and Pauly, Daniel, eds. (2008). "Mormyrops anguilloides" in FishBase. December 2008 version.
- Günther, A. (1866). Catalogue of the Fishes in the British Museum. The Trustees.
- Breden, C.M. (Jr.) and Rosen, D.E. (1966). Modes of Reproduction in Fishes. Garden City, New York: The Natural History Press.
- Arnegard, M.E. and Carlson, B.A. (2005). "Electric organ discharge patterns during group hunting by a mormyrid fish". Proceedings of the Royal Society 272 (1570): 1305–1314. doi:10.1098/rspb.2005.3101. PMC 1560340. PMID 16006329.
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- Gill, T. (1906). "Parental Care Among Fresh-Water Fishes". Annual Report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution.
- Lévêque, C. (1997). Biodiversity Dynamics and Conservation: The Freshwater Fish of Tropical Africa. Cambridge University Press. ISBN 0-521-57033-6.
- Paugy, D. (2002). "Reproductive strategies of fishes in a tropical temporary stream of the Upper Senegal basin: Baoulé River in Mali". Aquatic Living Resources 15: 25–35. doi:10.1016/S0990-7440(01)01144-5.
- Cornish Jack (Mormyrops deliciosus). Tourette Fishing. Retrieved on December 4, 2008.