Osteoglossiformes

(Bony tongues and relatives)

Class Actinopterygii

Order Osteoglossiformes

Number of families 6

Evolution and systematics

The osteoglossiformes are an unusual group of teleost fishes comprising about 220 species of freshwater fishes, most of which are in one African family, the Mormyridae (19 genera; 182 species). The other species are scattered about the continents and are generally considered to be relicts of a once more abundant group. Fossil records of the family Osteoglossidae indicate these fishes to be between 38 and 55 million years old. However, the present distribution of members of the Osteoglossidae family suggests that the group was present on Gondwana prior to Gondwana's fragmentation. Biogeographic evidence thus suggests a considerably greater age than the 55 million years inferred from the fossil record. Most osteoglossiformes have most of their teeth located on the tongue and on the roof of the mouth. They also have a caudal fin with 16 or fewer branched rays (most bony fishes have more), lack intermuscular bones on the back, and have cycloid scales with ornate microsculpturing. The intestine curls around to the left side of the esophagus rather than to the right as in most other bony fishes.

Six living families are recognized. The monotypic family Gymnarchidae (Gymnarchus niloticus) together with the Mormyridae, comprises the superfamily Mormyroidea; this group is considered the sister group of the Notopteroidea (family Notopteridae; four genera and eight species). The position of the three remaining families is somewhat uncertain. The Osteoglossidae comprise seven species (four genera) and the Pantodontidae but one. The phylogenetic position of the Hiodontidae (two species) is not very clear. The two species of this family have a similar ear–swim bladder connection as do the clupeomorph fishes.

Recent data indicate the presence of a group of mormyrid fishes of the genus Brienomyrus in Gabon of uncertain taxonomic status. Morphological, physiological (electric discharge), and molecular genetic data indicate these fishes represent a species flock. A comparable situation is known from the East African lakes Victoria, Malawi, and Tanganyika. A very limited number of riverine cichlid species adjusted to lacustrine conditions and have evolved into a species flock now comprising more than 200 species in each lake and dominating the fish fauna of these lakes.

Physical characteristics

The Mormyridae, the elephantfishes, are odd-looking fishes ranging from 1.6 in to 5 ft (4 cm to 1.5 m) in length. The head morphology varies considerably related to feeding specializations: some species possess prolonged heads, others trunklike snouts or appendages on the lower jaw, hence the common name. The tail is often deeply forked and the caudal peduncle very narrow. The skin is thick and of high electrical resistance; all species indeed are weakly electric. The electric organ is located in the caudal peduncle. Larvae possess a larval electric organ in the lateral muscle. The electric field set up around the fish is used for electrolocation and electrocommunication. Related to this sensory modality is the enlarged cerebellum; thus brain volume, relative to body size, is roughly the same size as that of humans. Male elephantfishes in most species can be distinguished from females by the lobed, enlarged front part of the anal fin. The sperm of mormyrids lacks flagellum. In the remaining osteoglossiform fishes, sexual dimorphism is not very pronounced or lacking.

Gymnarchus niloticus, the only species of the family Gymnarchidae, can reach 5 ft (1.5 m) in length. It possesses a long snout and a long dorsal fin used for locomotion; the anal, caudal, and pelvic fins are absent. The fish produces sinusoidal weakly electric discharges.

The eight species of knifefishes of the family Notopteridae have long, strongly compressed bodies tapering to a point. The long anal fin extends from just behind the head to the tiny caudal fin, which it joins. The dorsal fin, which is absent from Xenomystus nigri, is small and featherlike, so these fishes are commonly called featherbacks. The swim bladder is connected to the gut and is used for air breathing. The species of the African subfamily Xenomystinae, genera Xenomystus and Papyrocranus, possess cutaneous electroreceptors. Knifefishes range from 7.9 in (20 cm) in length (in Xenomystus nigri) up to 5 ft (1.5 m) (in Chitala lopis, the giant featherback).

Species of the family Osteoglossidae, the bony tongues, have heavy, elongate bodies covered with large scales. The dorsal and anal fins are long and placed on the rear part of the body. All these fishes can apparently breathe air with their lunglike swim bladders. Arapaima gigas can reach lengths of about 14.7 ft (4.5 m); other species attain lengths of about 3.3 ft (1 m).

The African freshwater butterflyfish, the only species of the family Pantodontidae, reach 3.9 in (10 cm) in length. The fishes possess a large gape and a straight dorsal profile. The pelvic fins with the prolonged fin rays are located under the greatly enlarged, winglike pectorals. The swim bladder can act as an air-breathing organ.

The two species of the family Hiodontidae, the mooneye (Hiodon tergisus) and the goldeye (H. alosoides), superficially resemble clupeid fishes. Their most distinctive external features are their large eyes, which have bright gold irises (goldeye) or gold/silver irises (mooneye). Goldeyes have only rods in their retinas and are known to feed mostly at night.

Distribution

Elephantfishes occur all over tropical Africa. The highest diversity is found in the Congo River basin, where mormyrids comprise about 20% of the total number of about 600 fish species. Gymnarchus niloticus is found in all large rivers of the Sahelo/Sudanean region in Africa.

African knifefishes inhabit coastal streams in West Africa (Xenomystus nigri and Papyrocranus afer), or the Congo basin (P. congoensis). The Asian knifefishes are found in the Indus, Ganges-Brahmaputra, and Mahanadi River basins in India (Chitala chitala), in Indonesia, Malaysia, and Thailand (Chitala lopis), and in Laos, Thailand, Cambodia, and Vietnam (Chitala ornata). Notopterus notopterus is very widely distributed, inhabiting rivers in India, Indochina, Thailand, Malaysia, and Indonesia.

The three South American bony tongues are either restricted to the Rio Negro (Osteoglossum ferreira), or occur in the Amazon River system and French Guiana (Arapaima gigas and O. bicirrhosum). Heterotis niloticus occurs in Africa in all river basins of the Sahelo/Sudanian region. The Asian bony tongue (Scleropages formosus) is native to Indonesia, Malaysia, Thailand, Cambodia, and Vietnam. S. jardini is found in New Guinea and Northern Australia; S. leichardti is restricted to northeastern Australia.

Pantodon buchholzi, the only representative of the family Pantodontidae, occurs in various rivers of central and West Africa.

The two species of Hiodon are found in the central part of North America, with H. alosoides being more widely distributed than H. tergisus.

Habitat

African elephantfishes are mainly riverine species and rarely occur in lakes. They are pelagic, midwater, or bottom-oriented fishes. The knifefishes inhabit stagnant backwaters of the large rivers, and are sometimes found in lakes; the smaller species prefer habitats with dense vegetation. Large bony tongues are found in open, slow-moving, or stagnant water and are surface-oriented hunters. Pantodon buchholzi prefers surface water of habitats with stagnant water. Hiodon alosoides lives in turbid waters in large lakes and muddy rivers, occasionally in swift current. H. tergisus is usually found in the clear waters of large lakes and streams.

Behavior

Elephantfishes are nocturnal, often hiding during the day in dense vegetation or under other kinds of cover. Aquarists have long admired mormyrids for their learning abilities and the fact that many species engage in apparent "play" behavior consisting of batting around small objects, including air bubbles, with the head. They usually swim slowly with their body rigid, presumably to avoid distorting the electrical field they are generating. The electric field is used for electrolocation and electrocommunication. The frequency of the electric signals can be modified to communicate with other fish, and thus can be used in courtship, aggressive behavior, and other intraspecific encounters. Because each species has its own set of electrical patterns, recognition and avoidance of other species is also possible. Mormyrids possess a well-developed sense of hearing; a part of the small swim bladder is in contact with the inner ear. Mormyrids use acoustic signals during courtship behavior. Gymnarchus niloticus, the close relative of the mormyrids, produces sinusoidal electrical discharges (the elephantfishes produce pulse-type discharges); this slow moving fish also uses its discharge for electrolocation. Knifefishes generally remain quietly in cover during daytime, but come out to prey in the evening. Bony tongued fishes are active during the day, spending most of the time patrolling very close to the surface. From aquaculture and aquarium observations, it has been deduced that the Australian spotted barramundi (Scleropages leichardti) can withstand water temperatures of between 44.6 and 104°F (7 and 40°C). During the summer, when surface temperatures exceed 87.8°F (31°C) in their natural habitat, surface cruising ceases and the fish remain in deeper, cooler areas. Pantodon buchholzi is a slow-moving fish of surface waters; it can jump out of the water and has been observed gliding over 13.1–16.4 ft (4–5 m). The pronounced tapetum lucidum of the two Hiodon species enables these fishes to hunt effectively at night.

Feeding ecology and diet

The mormyrid fishes eat various kinds of zooplankton or feed on a variety of benthic organisms such as insect larvae, crustaceans, oligochaets, and snails. The species with the long snouts find their prey in holes and crevices. Large Mormyrops species are piscivorous. Elephantfishes themselves are eaten by the large predator Gymnarchus niloticus (who also feeds on other fishes) and large piscivorous catfishes. Smaller knifefishes feed on insect larvae, crustaceans, worms, and snails; the larger species are mainly piscivorous. The bony tongues are midwater and surface feeders. Species of the genus Osteoglossum and Scleropages are carnivorous, feeding in roughly equal measure upon smaller fishes and terrestrial insects. While large specimens of both are known to take small terrestrial vertebrates opportunistically, these items do not constitute a significant portion of their diet in nature. The large Arapaima gigas prefers fishes. Heterotis niloticus has its fourth gill arch modified into a spiral-shaped filtering apparatus. This organ secretes mucus in which phytoplankton and bits of organic matter are trapped and then swallowed. The surface-oriented Pantodon buchholzi lives on crustaceans, insects, and small fishes. The two species of the family Hiodontidae feed on a variety of prey, including aquatic insects, crustaceans, mollusks, small fishes, frogs, shrews, and mice. They are preyed upon by birds, some mammals, and other fishes.

Reproductive biology

Most osteoglossiform fishes breed during the rainy season. Experimental studies with elephantfishes have shown that gonad maturation is triggered by decreasing water conductivity. About nine species have been bred in captivity. Parental care in the male is found in Pollimyrus isidori; the eggs are transported after oviposition by the male into the nest of about 2 in (5 cm) in diameter, generally made from plant material. After hatching (three days after fertilization) the male guards the embryos until the beginning of exogenous feeding (on days 13–14) and also during the larval period. Courtship behavior is characterized by acoustic and electrical behavior. Species of the genus Stomatorhinus probably also show parental care. The remaining species bred so far (Petrocephalus

soudanensis, Brienomyrus brachyistius, Marcusenius sp., Mormyrus rume proboscirostris, Mormyrus sp., Hippopotamyrus pictus, Campylomormyrus cassaicus, and C. phantasticus) do not show parental care.

Egg size ranges between 0.07 in (1.8 mm) in P. soudanensis) and 0.12 in (3 mm) in H. pictus. Eggs number between a few hundred in P. isidori, and more than a thousand in C. cassaicus. Spawning intervals range between a few days in P. isidori and several weeks in most other species.

Gymnarchus niloticus breeds in swamps during the high-water season. Prior to spawning, these fishes construct a floating nest of plant fibers in which the thousand or so eggs, each about 0.39 in (10 mm) in diameter, are laid. The newly hatched young have long gill filaments and an elongate yolk sac. They come to the surface for air. Young fishes feed on insects and other invertebrates.

Reproduction in knifefishes is not well known. Xenomystus nigri females lay 150–200 eggs of 0.08 in (2 mm) diameter; in Notopterus notopterus, eggs (1,000–3,000) are deposited in small clumps on submerged vegetation. Chitala chitala lays eggs on a stake or stump of wood, the male fans them with his tail and guards them against predators. Arapaima gigas males build a nest about 6 in (15 cm) deep and 20 in (50 cm) wide in sandy bottoms at the end of the dry season; the large eggs and young are guarded by the male and occasionally by the female. Parental care lasts up to 14 weeks. The two Osteoglossum species are male mouth brooders. The large eggs (about 0.6 in/16 mm diameter) are incubated for 50–60 days. At release, the juveniles measure 3.1–3.9 in (8–10 cm).

The Scleropages species are female mouth brooders. S. leichardti incubates 70–200 eggs about 0.4 in (10 mm) in diameter. Spawning occurs in small ponds during spring, when water temperatures rise to 68–73.4°F (20–23°C). Hatching takes place between one and two weeks after spawning; the embryos with their large yolk sac are about 0.6 in (15 mm) long. After the total incubation period of five to six weeks, the juveniles are released at a total length of about 1.4 in (35 mm). During a three-day period, the female shows a "release-and-recall" behavior. When the young become independent of the female, they take up territories around the edge of the pond. Heterotis niloticus is a nest builder, breeding in still waters close to the river, and excavating a nest some 3.9 ft (1.2 m) in diameter with thick walls of vegetation and mud. Within this nest, eggs about 0.1 in (2.5 mm) in diameter are laid; protected by the parents; they hatch in two days. The newly hatched embryos have external gills. Pantodon buchholzi has a prolonged spawning season, spawning 80–200 small buoyant eggs every day; the small embryos hatch after 36 hours. Goldeye (Hiodon alosoides) spawn in late spring on gravelly shallows of tributary streams. Their eggs are about 0.16 in (4 mm) in diameter, and are semibuoyant even after hatching, as the oil globule in the yolk buoys up the newly hatched 0.3 in (7 mm) embryo.

Conservation status

Four species are listed by the IUCN: Arapaima gigas is listed as Data Deficient; Chitala blanci is listed as Lower Risk/Near Threatened; Scleropages formosus is listed as Endangered; and Scleropages leichardti is listed as Lower Risk/Near Threatened. Scleropages formosus is also included on Appendix I of CITES, as a result of which international trade is banned (CITES Appendix I). For Arapaima gigas, international trade is restricted (CITES Appendix II).

Significance to humans

Most osteoglossiform fishes, particularly the larger species, are economically important food fishes. Even many of the medium-sized African elephantfishes, which measure approximately 7.9–23.6 in (20 to 60 cm) in length, are regularly fished for food. Some of the larger osteoglossiforms are used in aquaculture, including Arapaima gigas; Scleropages leichardti and S. jardini; Heterotis niloticus; Chitala blanci and C. chitala; and Notopterus notopterus. The larger species are important as food fishes, as well as for exhibition in public aquaria. The various color breeds of Scleropages formosus are favored as ornamental fishes in Asia. The elephantfish, Gnathonemus petersii, is a well-known species in the international aquarium trade. Several species of the weakly electric mormyrids are intensively studied by scientists.

Species accounts

List of Species

Aba-aba

Gymnarchus niloticus

family

Gymnarchidae

taxonomy

Gymnarchus niloticus Cuvier, 1829, Nile River.

other common names

German: Nilhecht.

physical characteristics

Maximum size 5.48 ft (1.67 m) at 40.8 lb (18.5 kg). Heavy elongate fishes covered with small scales. Have long anal fin tapering in a short caudal appendage, lack dorsal, pelvic, and caudal fins. Caudal part can regenerate after injury. Anal fin used for propulsion. Weakly electric fish.

distribution

Large rivers and back waters of the Sahelo and Sudanian regions of Africa

habitat

Back waters with slow-moving or stagnant water, vegetation, and various kinds of cover.

behavior

Nocturnal; hides during daytime. Very aggressive towards conspecifics. Weakly electric discharges of the sinusoidal type used for electrolocation.

feeding ecology and diet

Piscivorous, ecology not well known.

reproductive biology

Breeds in swamps during the high-water season. Prior to spawning, a floating nest of plant fibers is created, most probably by the male. 1,000 or so eggs, each about 0.16 in (4 mm) in diameter, are laid in the nest. The newly hatched young have long gill filaments and an elongate yolk sac. They come to the surface for air. Young fishes feed on insects and other invertebrates. Parental males defend the nest very aggressively and do not hesitate to attack and bite human intruders. It is quite common to see fishermen in West Africa with the distinctive half moon–shaped scars left by an Aba-aba attack.

conservation status

Not listed by the IUCN.

significance to humans

Very important food fish. Risk of overexploitation due to low reproductive capacity (low number of fry).

Mooneye

Hiodon tergisus

family

Hiodontidae

taxonomy

Hiodon tergisus LeSueur, 1818, Lake Erie at Buffalo, New York, and Ohio River at Pittsburgh, Pennsylvania, United States.

other common names

None known.

physical characteristics

Maximum size 17 in (43 cm). Resembles clupeid or cyprinid fishes with large eyes and large oblique gape. The tapetum lucidum of the retina gives the silvery appearance of the eye.

distribution

St. Lawrence River and the Great Lakes (except Lake Superior) in Canada and United States; Mississippi River in the United States, Hudson Bay basins from Quebec to Alberta in Canada, and south to Gulf of Mexico. Gulf slope drainages from Mobile Bay in Alabama to Lake Pontchartrain in Louisiana.

habitat

Deep pools and backwaters of medium to large rivers, lakes, and impoundments; prefers clear water.

behavior

The specialized eyes allow the fishes to forage at low light intensities.

feeding ecology and diet

Insects, insect larvae, and small fishes.

reproductive biology

Reproduction biology probably similar to that of the related species H. alosoides. Spawning occurs in late spring on gravelly shallows of tributary streams. Eggs are about 0.16 in (4 mm) in diameter and are semibuoyant due to oil globules.

conservation status

Not listed by the IUCN.

significance to humans

The species is locally exploited for food.

Elephantnose fish

Gnathonemus petersii

family

Mormyridae

taxonomy

Gnathonemus petersii Günther, 1862, "Old Calabar, Westafrika."

other common names

English: Peter's elephantnose; German: Tapirfisch, Elefanten-Rüsselfisch, Spitzbartfisch.

physical characteristics

Maximum length 9.8 in (25 cm). Slender, laterally compressed fish with long dorsal and anal fin located at the rear part of the body. Narrow caudal peduncle houses the weakly electric organ. Caudal fin deeply forked. Body coloration dark brown to black. Two whitish transversal bands at the beginning and in the middle of dorsal and anal fins. Chin barbel on lower jaw.

distribution

West Africa from Niger to Congo River basins. Limited to the Lower Niger, in the Ogun, in the Cross River Basin and in the Upper Chari.

habitat

Habitat not very well known, but probably slow-moving waters of large rivers.

behavior

Social and nocturnal. Often occurs in large schools. Weakly electric discharges of the pulse type used for electrocommunication. Captive animals appear to have a complex social structure, with a nonlinear "peck order."

feeding ecology and diet

Bottom-oriented, feeds on invertebrates of soft substrate.

reproductive biology

Not known. Probably spawns during the rainy season.

conservation status

Not listed by the IUCN.

significance to humans

Most important mormyrid species in the international fish trade. Known to aquarists for their "play" behavior. Often used in scientific studies concerning neuroanatomy, physiology, and behavior.

No common name

Mormyrus rume proboscirostris

family

Mormyridae

taxonomy

Mormyrus rume proboscirostris Boulenger, 1898, "Upoto" Upper Congo.

other common names

Chokwe (Angola): Sosha.

physical characteristics

Maximum length about 13.7 in (35 cm). Elongate fishes with very long dorsal fin, short anal, and forked caudal fin. Snout prolonged and curved downward, dolphinlike. Electric organ in adults in the caudal peduncle; in the lateral muscle of young fish a larval electric organ is found. Mormyrus is the only mormyrid genus whose members produce weakly electric discharges of up to 30 V, which can be felt by touching the caudal peduncle of the fish. Body coloration dark gray.

distribution

Congo River basin in Africa.

habitat

Not known.

behavior

Very active both day and night. Very social fish, however with many aggressive interactions that can cause death of subordinate specimens.

feeding ecology and diet

Feeds on insect larvae, crustaceans, and mollusks, as well as small fishes. Produces fine jets of water with the tubular mouth in search for prey in the substrate.

reproductive biology

Reproduction occurs during the high-water season. Gonad maturation can be provoked experimentally by decreasing conductivity for several weeks. During each fractional spawning event several hundred eggs of 0.1 in (2.5 mm) in diameter are deposited. Hatching on day three. Exogenous feeding starts on day 10–11. Spawning intervals three to four weeks. No parental care.

conservation status

Not listed by the IUCN.

significance to humans

All Mormyrus species are economically important as food fishes.

Elephantfish

Pollimyrus isidori

family

Mormyridae

taxonomy

Pollimyrus isidori Valenciennes, 1847, "Westafrika."

other common names

None known.

physical characteristics

Maximum length 3.94 in (10 cm). Broad, laterally compressed fish with long dorsal and anal fins located at the rear part of the body. Slightly subterminal mouth. Weakly electric organ found in the narrow caudal peduncle. Larval electric organ in the lateral muscle of larvae up to 1 in (25 mm) long. Body coloration uniform gray and black.

distribution

Nile River, Upper and Middle Niger, Chari, and Lagone River systems, including Lake Chad. Disjunctly distributed in the coastal rivers of West Africa between the Niger and the Sénégal.

habitat

Slow-moving water and back waters of rivers; lakes.

behavior

Nocturnal and territorial. Males occupy territories of 3.3–9.8 sq ft (1–3 sq m). Pronounced acoustic signaling during courtship behavior.

feeding ecology and diet

Insect larvae, crustaceans, and small mollusks.

reproductive biology

Reproduction occurs during the rainy season. Parental care in the male. Thirty to 200 eggs 0.1 in/2.5 mm in diameter are deposited in a nest of plant material. Free embryos and larvae are also guarded; exogenous feeding starts on days 13–14. Spawning intervals five to 20 days.

conservation status

Not listed by the IUCN.

significance to humans

Best-studied mormyrid fish in science concerning reproductive biology.

Clown knifefish

Chitala chitala

family

Notopteridae

taxonomy

Chitala chitala Hamilton, 1822, type locality unknown (probably India or East Indies).

other common names

English: Clown featherback; German: Indischer Messerfisch.

physical characteristics

Up to 31.5–35.4 in (80–90 cm) long. Strongly compressed, tapering to a point. Very long anal fin continuous with the caudal, small dorsal fin. Dorsal profile is markedly convex. Small pelvic fins unite together at their base.

distribution

Indus, Ganges, Brahamaputra, and Mahandi River basins in India.

habitat

Rivers, canals, reservoirs, and ponds.

behavior

Generally remains quietly in cover during daytime, but comes out to prey at night.

feeding ecology and diet

Aquatic insects, mollusks, shrimps, and small fishes.

reproductive biology

Spawns once a year during May to August. Eggs usually laid on wooden substrate, male fans them with tail and keeps them aerated and silt free. Eggs are guarded against small catfishes and other predators. Embryos hatch after one week and are guarded by the male for some days.

conservation status

Not listed by the IUCN.

significance to humans

Moderately important food and game fishes also used in aqua-culture. Large specimens are often exhibited in public aquaria.

Arapaima

Arapaima gigas

family

Osteoglossidae

taxonomy

Arapaima gigas Schinz, 1822, probably Amazon River.

other common names

English: Pirarucu; German: Paiche; Spanish: Paíche; Portuguese: Piracuçu.

physical characteristics

Heavy elongate fishes with large, ornate scales. One of the largest freshwater fishes, reaching 15 ft (4.5 m) in length and 441 lb (200 kg). Pelvic and unpaired fins located posteriorly.

distribution

Amazon River system and French Guiana.

habitat

Midwater fishes found in open, slow-moving, or stagnant water.

behavior

Slow-moving, air-breathing fishes that surface every 10–20 minutes. This behavior makes it an accessible target for harpoon fishermen. Sometimes aggressive toward conspecifics.

feeding ecology and diet

Swallow fish and other large prey. The diet also includes heavily armored loricariid catfishes. Ecology in general not well studied.

reproductive biology

Breed at the end of the dry season. Male builds nest about 6 in (15 cm) deep and 19.7 in (50 cm) wide in sandy bottoms at the end of the dry season. Large eggs and young are guarded by the male and occasionally by the female. Parental care lasts up to 14 weeks.

conservation status

Listed as Data Deficient by the IUCN. Heavily overfished. The unsustainable and environmentally destructive practice of fishing for this species using dynamite during the breeding season has resulted in the loss of breeding pairs and their fry. This practice is one of the chief reasons for the dramatic decline of this species in western Amazonia. International trade restricted; listed on Appendix II of CITES.

significance to humans

One of the most important food and game fishes of Amazonia. Also used in aquaculture. Popular fish in public aquaria.

Arawana

Osteoglossum bicirrhosum

family

Osteoglossidae

taxonomy

Osteoglossum bicirrhosum Cuvier, 1829, Amazon River.

other common names

English: Silver aruana, aruana; German: Arabuana, Gabelbart.

physical characteristics

Maximum size 3.3 ft (1 m). Large-scaled, elongate fishes, laterally compressed with straight dorsal provile and large gape. Very long anal and dorsal fins nearly joining the caudal fin. Prominent barbels at the tip of the chin.

distribution

Amazon River system and French Guiana.

habitat

Surface-orientated, live in open, slow-moving or stagnant water, preferably at the shore zone.

behavior

Day active, spends most of the day patrolling very close to the surface.

feeding ecology and diet

Omnivorous, mainly eat invertebrates, or fishes to a lower percentage. Frequently jump out of the water to seize small vertebrates and large (particularly terrestrial) insects.

reproductive biology

Reproduction takes place at the beginning of the floods, in general in December and January. About 200 large eggs 0.63 in (16 mm) in diameter are incubated in the males' mouth for 50–60 days. When released, juveniles are 3.15–3.93 in (8–10 cm) long.

conservation status

Not listed by the IUCN.

significance to humans

An important food fish of Amazonia. Of special value in caboclo (person of mixed Brazilian, Indian, European, or African ancestry) folklore because it is one of the few species that women are allowed to eat postpartum; other species, especially catfishes, are thought to cause inflammation if eaten in times of illness and recovery.

Freshwater butterflyfish

Pantodon buchholzi

family

Pantodontidae

taxonomy

Pantodon buchholzi Peters, 1877, Victoria River, Cameroon.

other common names

French: Poísson papillon; German: Schmetterlingsfisch.

physical characteristics

Small (up to 3.94 in/10 cm), surface-oriented fishes with straight dorsal profile and large, winglike pectorals; prolongated fin rays on the pelvic fins. Upper part of the body olive, ventral part silvery yellow amplified with red.

distribution

Lower Niger, Lake Chad, Cameroon, Ogooué, Congo River basin, and Upper Zambezi of Africa. A relict population might be present in Sierra Leone in Western Africa.

habitat

Surface water of habitats with stagnant water.

behavior

Lives in schools underneath surface. Can jump out of the water for feeding or to escape predators. While this species has been observed gliding at distances between 13.1–16.4 ft (4–5m), and even over 49.2 ft (15 m), this behavior needs to be documented and is highly controversial. The anatomy of the pectoral and ventral fins in this species display none of the anatomical modifications that would allow it to make long glides, nor does it possess the sort of hypertrophied pectoral musculature that permits powered flight.

feeding ecology and diet

Crustaceans, insects, and small fishes.

reproductive biology

Prolonged spawning season. Spawning occurs preferably at night. Between 80–200 buoyant eggs, 0.12 in (3 mm) in diameter, are laid each night. The embryos hatch after 36 hours at 78.8°F (26°C) and are 0.43 in (11 mm) long. Raising is not easy as the fry need live food near the surface. Growth is rather quick; after one year individuals can reach 0.39 in (10 cm) in length and can begin to spawn.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Bullock, T., and W. Heiligenberg. Electroreception. New York: John Wiley & Sons, 1986.

Daget, J., J. P. Gosse, and D. F. E. Thys van den Audenaerde, eds. Check-List of the Freshwater Fishes of Africa (CLOFFA), Vol. 1. Paris: ORSTOM, Tervuren: MRAC, 1984.

Merrick, J. R., and G. E. Schmida. Australian Freshwater Fishes, Biology and Management. North Ryde, Australia: School of Biological Sciences, 1984.

Moller, P., ed. Electric Fishes: History and Behavior. London: Chapman & Hall, 1995.

Periodicals

Kirschbaum, F. "Reproduction and Development of the Weakly Electric Fish Pollimyrus isidori (Mormyridae, Teleostei) in Captivity." Env. Biol. Fishes. 20 (1987): 11–31.

Kirschbaum, F., and C. Schugardt. "Reproductive Strategies and Developmental Aspects of Gymnotiform and Mormyrid Fishes." J. Physiol., in press.

Roberts, T. R., "Systematic Revision of the Old World Freshwater Fish Family Notopteridae." Ichthyological Explorations of Freshwaters 2, no. 4 (1992): 361–383.

Frank Kirschbaum, PhD