Taxonomy & naming
Polypterus ansorgii was described by the Belgian-British ichthyologist George Albert Boulenger in 1910, with its type locality given as the Corubal River in Guinea-Bissau. It belongs to the genus Polypterus in the family Polypteridae, order Polypteriformes — the bichirs and the reedfish, which together form the most basal living lineage of the ray-finned fishes (Actinopterygii). This is a branch of the fish tree that split off before almost every other feature familiar from a modern bony fish evolved, and its members are genuine living fossils, carrying a suite of primitive traits — armoured scales, paired lungs, larvae with external gills — that the rest of the ray-finned fishes lost long ago.
The species name honours Dr. William John Ansorge (1850–1913), an English physician, explorer and collector who gathered natural-history specimens across West and Central Africa in the early twentieth century, several of which passed through Boulenger's hands at the Natural History Museum in London. FishBase lists it under the common name Guinean bichir, reflecting its distribution centred on Guinea and Guinea-Bissau. As with several of its relatives, the species has a history of confusion in both museum and field records with other similarly built Polypterus from the same region, and its taxonomy is not among the best resolved in the genus.
Morphology
Polypterus ansorgii shows the classic bichir build: an elongated, near-cylindrical body, flattened slightly along the belly, sheathed from head to tail in thick, interlocking ganoid scales — rhombic plates of bone capped with a hard, enamel-like layer — that form a flexible suit of natural armour. In place of a single dorsal fin it carries a row of separate finlets, reported at 13 to 15 in this species, each a short spine trailing a small flag of membrane; the exact finlet count is one of the characters used to tell Polypterus species apart. The paired pectoral fins sit on thick, muscular lobes that the fish uses to prop itself up and shuffle along the substrate almost like limbs.
Size in this species is unusually uncertain. FishBase's scientific record lists a modest maximum of about 11 in total length, but field and hobbyist reports — including specimens said to have measured up to roughly 33.9 in from the River Koliba — suggest some populations, or perhaps misidentified relatives, grow considerably larger. That gap between museum specimens and field claims has not been resolved, and it is best treated as an open question rather than a settled fact. As in all bichirs, the eyes are small and vision is poor; the fish instead relies on a keen sense of smell to find food and navigate in low light.
Habitat
The Guinean bichir is a West African endemic, known from the Corubal River in Guinea-Bissau, the Niger basin in Guinea, and further east from Lake Kainji and the Ogun River in Nigeria — a scattered range across the Upper Guinea coastal river systems and the upper Niger drainage. These are warm, forest- and savanna-fringed lowland rivers typical of the West African littoral, generally soft and mildly acidic to circumneutral in chemistry, though the exact character of each population's home water is not well documented in the literature.
As in every Polypterus, a pair of primitive lungs lets this fish exploit water too warm, still or oxygen-poor for gill-breathing fish alone, rising to gulp air at the surface. That physiology is what allows bichirs to persist in shallow floodplain pools, backwaters and marginal habitat across the wet and dry seasons of the West African tropics, even where dissolved oxygen runs low.
Feeding
Polypterus ansorgii is a carnivorous ambush predator, hunting mostly after dark by smell rather than sight. Reported prey includes small fish, aquatic insect larvae, crabs and shrimp — the same broad, opportunistic menu of invertebrates and small vertebrates taken by other Polypterus, seized with a quick sideways snap once the fish has closed the distance by scent alone.
In captivity it takes meaty foods readily: whole or chopped fish, prawn, mussel, earthworms and other live or frozen invertebrate foods. Because it is a slow, deliberate feeder that locates food by smell, it can be out-competed by faster tankmates at feeding time and often does best fed after lights-out or with food placed close to where it is resting.
Mating
Species-specific courtship observations for Polypterus ansorgii are not documented in the available literature, but the mechanism is uniform across the bichirs and there is no reason to expect this species differs. Fertilisation is external: the male follows a ripe female and cups his thickened, muscular anal and pelvic fins into a shallow pouch, into which she releases a few small, adhesive eggs at a time; the male fertilises them in this cradle before they are scattered onto plants and the substrate. The sequence repeats over hours as the pair works through a spawn.
As in other Polypterus, the male's broader, thicker anal fin — the fin used to form the fertilisation pouch — is likely the chief external difference between the sexes, though this has not been specifically confirmed for the Guinean bichir.
Breeding
Like the rest of the family, Polypterus ansorgii is an egg-scatterer with external fertilisation and no parental care: adults take no further interest in the adhesive eggs once they are laid among plants and will eat both eggs and fry if given the chance. Bichir eggs typically hatch within a few days into small larvae bearing feathery external gills behind the head, much like the tadpoles of a newt, which are absorbed as the young mature.
There are no documented reports of this species being bred in the home aquarium, and virtually all Guinean bichirs in the trade are wild-caught rather than farm-raised — unlike the Senegal bichir, which is now produced commercially. Spawning in bichirs generally needs seasonal or flood-like cues that are difficult to replicate reliably in a tank, so successful captive breeding of this species should be treated as rare to unrecorded.
In the aquarium
Polypterus ansorgii is seldom offered in the trade and, when available, is a fish for an experienced keeper with a large, secure setup. Sources report water parameters of roughly 77–82 °F and a pH from about 5.5 up to 7.5 — soft to neutral, mildly acidic water — and recommend a tank of at least 180 US gallons (roughly 180 US gal or more) for an adult, reflecting the uncertainty over just how large this species can grow. A soft sand substrate, driftwood and dim lighting suit its nocturnal habits.
Two points of husbandry outweigh everything else. First, the lid: bichirs are proficient jumpers and determined escape artists, and the tank must be fully and tightly covered while still leaving an air gap at the surface for the fish to breathe — a bichir found dried out on the floor is the most common way keepers lose one. Second, tankmates: this is a predator that will eat anything small enough to swallow, so companions need to be too large to fit in its mouth and calm enough not to provoke or outcompete it; avoid aggressive or territorial species. Given those conditions it is otherwise a hardy, long-lived fish, protected by its ganoid armour and more forgiving of routine medications than scaleless catfish.
Conservation
Polypterus ansorgii is assessed as Least Concern on the IUCN Red List. It is a West African endemic with a patchy but multi-country range across Guinea-Bissau, Guinea and Nigeria, and it does not currently meet the criteria for a more threatened category.
Because it is infrequently surveyed and rarely targeted specifically by researchers, population trend data is limited, and the wide discrepancy between museum-recorded and field-reported sizes hints at how little dedicated study this species has received. As with other West African freshwater fish, habitat degradation from damming, deforestation and water pollution in its home rivers is a plausible long-term pressure, though there is no cache-documented evidence of a current species-specific decline.