The freshwater butterflyfish or African butterflyfish (''Pantodon buchholzi'') is a species of osteoglossiform fish native to freshwater habitats in the

Niger Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...

and Congo basins of western and central Africa. It is the only

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

species in the family Pantodontidae. It is not closely related to saltwater butterflyfishes.

Evolution

The freshwater butterflyfish is the last surviving member of a family that was diverse during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

period, with many pantodontid genera known from the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

-aged Sannine Formation of

Lebanon Lebanon, officially the Republic of Lebanon, is a country in the Levant region of West Asia. Situated at the crossroads of the Mediterranean Basin and the Arabian Peninsula, it is bordered by Syria to the north and east, Israel to the south ...

. These early pantodontids inhabited a marine environment off the coast of northern Africa and are the earliest known marine osteoglossomorphs, suggesting that the ancestors of ''Pantodon'' colonized freshwater habitats independently of other osteoglossiforms. These Cretaceous marine pantodontids appear to vary in their relation to the extant genus; of them, the closest relative and sister genus to ''Pantodon'' appears to be '' Palaeopantodon''. Populations of freshwater butterflyfish in the Niger vs. the Congo basins appear virtually identical in morphology, but mtDNA divergence estimates suggest an extreme level of genetic divergence between them, dating to the

Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

(57 million years ago) or earlier. This is one of the most dramatic cases of morphological stasis (in which two allopatric populations remain similar in appearance despite achieving a great level of genetic divergence from one another) known in a vertebrate taxon, and may suggest some level of cryptic speciation within the genus. Genetic studies suggest that the freshwater butterflyfish has experienced one of the greatest losses of whole ''Hox'' gene clusters in a

teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

fish, with only 5 ''Hox'' clusters present after a presumed loss of 3 ''Hox'' clusters in the past. Despite this, it retains a similar overall number of ''Hox'' genes to other teleosts, due to a high proportion of duplicated genes in certain clusters. Due to its small size, widespread availability in captivity, and relatively small genome, the freshwater butterflyfish may serve as an attractive

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

, despite being studied less compared to other model fish taxa, which are clupeocephalans.

Description and habits

Freshwater butterfly fish are small, no more than in length, with very large

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s. It has a large and well-vascularized swim bladder, enabling it to breathe air at the surface of the water. It is carnivorous, feeding primarily on aquatic

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s and smaller fishes. The freshwater butterflyfish is a specialized surface hunter. Its eyes are constantly trained to the surface and its upturned mouth is specifically adapted to capture small prey along the water's surface. If enough speed is built up in the water, a butterflyfish can jump and glide a small distance above the surface to avoid predation. It also wiggles its pectoral fins as it glides, with the help of specialized, enlarged pectoral muscles, the ability which earned the fish its common name. When freshwater butterflyfish spawn, they produce a mass of large floating eggs at the surface. Fertilisation is believed to be internal. Eggs hatch in about seven days.

Distribution

Freshwater butterflyfish are found in the slightly acidic, standing bodies of water in West Africa. They require a year-round temperature of . They are found in slow- to no-current areas with high amounts of surface foliage for cover. They are commonly seen in

Lake Chad Lake Chad (, Kanuri language, Kanuri: ''Sádǝ'', ) is an endorheic freshwater lake located at the junction of four countries: Nigeria, Niger, Chad, and Cameroon, in western and central Africa respectively, with a catchment area in excess of . ...

, the Congo Basin, throughout lower

Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...

, Ogooue, and upper Zambezi. They have also been seen in the Niger Delta, lower Ogooue, and in the lower Cross River.

In the aquarium

Freshwater butterflyfish are kept in large aquaria, although a single specimen should be kept as the only top-level fish, as they can be aggressive to their own kind and others, (such as hatchetfish), at surface level. The tops of the tanks must be tightly closed because of their jumping habits. They do better in a tank with live plants, especially ones that float near the surface, providing hiding places to reduce stress. They require a pH of 6.9–7.1, and a KH of 1–10. In aquaria, freshwater butterflyfish can grow to 5 inches long, and should be housed in 20 gallon long-style tanks (30.5 inches long) or larger. They should not be kept with fin-eating or aggressive fish, which may nip at their long, trailing fins. They eat any fish small enough to fit in their mouths, so they should be maintained with bottom-dwelling fish or top- and mid-dwelling fish too large in size to be bothered by them. They generally will not eat prepared food, and do best on a diet of live or possibly canned crickets and other insects, as well as live, gut-loaded feeder fish ( goldfish should be avoided). They prefer still water, so filtration should not be too powerful.

References

Bibliography