Taxonomy & naming
Polypterus congicus was described by the Belgian-British ichthyologist George Albert Boulenger in 1898, and sits in the genus Polypterus, family Polypteridae, order Polypteriformes — the bichirs and the reedfish, the most basal living lineage of the ray-finned fishes (Actinopterygii). These are true living fossils, retaining a suite of ancient features — ganoid armour, paired lungs, larvae with external gills — that the rest of the ray-finned fishes lost long ago.
According to the ETYFish Project, the species epithet congicus is a Latinised adjective meaning "belonging to the Congo Basin," a straightforward reference to the type locality at Stanley Falls (the cataracts on the upper Congo River near present-day Kisangani, Democratic Republic of the Congo). For much of the twentieth century this fish was often lumped as a form or subspecies of the Nile bichir, Polypterus endlicheri congicus; it is now recognised as its own valid species, P. congicus, distinct from P. endlicheri of the Nilo-Sudan rivers.
Morphology
The giant bichir shares the family's unmistakable body plan: a long, cylindrical, faintly flattened body clad in thick, glossy, interlocking ganoid scales — rhombic plates of bone capped with a hard, enamel-like layer — that form a flexible suit of armour tougher than that of almost any other aquarium fish. In place of a single dorsal fin it carries a row of separate finlets running from mid-back to the tail, each a small spine trailing a flag of membrane; FishBase records 12 to 15 of these dorsal finlets in this species, a useful identification character within the genus. The paired pectoral fins sit on thick, muscular, limb-like lobes that the fish uses to prop itself up and shove across the substrate.
P. congicus is the giant of the family. FishBase lists a maximum recorded total length of 38.2 in, with wild adults commonly reaching around 35.4 in — dwarfing the 25-to-13.8 in Senegal bichir most aquarists know. Aquarium specimens, raised in the confines of a tank, typically top out smaller, often around 23.6 in, but this is still a very large, heavy-bodied predator. As in all bichirs, eyesight is poor and the fish hunts chiefly by smell; behind the gills sits a pair of primitive, sac-like lungs, connected to the gut, with which the fish breathes air gulped at the surface — a bichir cut off from the surface can drown.
Habitat
Polypterus congicus is widespread through the Congo River drainage, one of the largest and most biodiverse river systems in Africa, and FishBase also records it from Lake Tanganyika, which drains into the Congo system via the Lukuga River. It is a freshwater, bottom-dwelling (demersal) species, generally found in shallow water from the surface down to around 33 ft, over mud and sand among vegetation and cover along river margins, backwaters and floodplain habitat typical of the Congo basin's warm lowland rivers.
As with other bichirs, its paired lungs are an adaptation to exactly this kind of environment: slow, warm, often oxygen-poor water where a fish able to gulp air at the surface has an advantage over gill-breathers alone. The type locality at Stanley Falls, a stretch of rapids and cataracts on the upper Congo River, sits well within the species' broader, evidently tolerant range across the Congo drainage.
Feeding
Like the rest of its family, the giant bichir is a carnivorous, nocturnal ambush predator that relies on smell far more than sight. It cruises slowly over the riverbed after dark, using its acute olfactory sense to locate prey before engulfing it with a fast sideways snap of the jaws; given its much larger adult size, wild P. congicus can be expected to take larger prey items than the smaller bichir species — fish, crustaceans, molluscs, amphibians and aquatic invertebrates it can subdue.
In the aquarium it feeds readily on meaty foods — bloodworms, brine shrimp and pieces of fish are all reported as accepted fare — and many individuals will also learn to take sinking pellets. Because it hunts by scent and moves deliberately, it is easily outcompeted by fast, aggressive tankmates at feeding time, and given its predatory size and appetite it must always be housed with fish too large to be swallowed.
Mating
Bichirs reproduce by external fertilisation using a distinctive courtship shared across the genus. A male follows a receptive female and cups his thickened, muscular anal and pelvic fins into a shallow pouch; the female releases a few eggs at a time into this pouch, and the male fertilises them there before the eggs — small and adhesive — are scattered onto plants and the substrate. This sequence is repeated over an extended spawning bout.
As in other Polypterus, the sexes are distinguished chiefly by this spawning apparatus: males have a visibly broader, thicker anal fin than females, most pronounced in breeding condition. Given the species' very large adult size, successful courtship and spawning require an unusually spacious setup, which is one reason breeding has rarely, if ever, been documented in home aquaria.
Breeding
Polypterus congicus is an egg-scatterer with no parental care: adhesive eggs are deposited among plants and substrate, and adults will readily eat both eggs and fry they encounter afterward. As in other bichirs, the eggs hatch within a matter of days into small larvae that carry feathery external gills behind the head — much like a salamander tadpole — which are absorbed as the fry mature and their internal gills and lungs take over.
Breeding this species deliberately in captivity is essentially unheard of; its huge adult size alone puts it well beyond the reach of most home fishrooms, and — as with most bichirs besides the farm-bred Senegal bichir — the trade continues to rely overwhelmingly on wild-caught individuals rather than captive-bred stock.
In the aquarium
The giant bichir is not a beginner's fish, and it is frequently sold far too small for what it becomes. Aquarium-care sources recommend a minimum of roughly 180 US gallons (about 180 US gal) for an adult — a long, wide footprint that reflects a fish that may approach a metre in length — furnished with soft sand, driftwood and secure hiding places, and kept dim to suit a nocturnal hunter. Reported water parameters are fairly forgiving: a temperature of about 72–82 °F (72–82°F), pH 6.0 to 8.0 and moderate general hardness (roughly 5–25°H), consistent with the broad tolerance typical of the genus. Its thick ganoid armour makes it hardier and more medication-tolerant than scaleless catfishes of similar size.
Two points outweigh everything else in keeping this species well. First, the lid: bichirs are notorious escape artists, and a fish this size pushing at a loose cover is a real hazard — the tank needs a complete, tightly fitted lid while still leaving an air gap so the fish can surface and breathe. Second, tankmates and scale: this is a large predator that will swallow anything that fits in its mouth, so companions must be too big to eat, calm, and — crucially — the tank itself must be sized for an adult from the outset, not the juvenile sold in the shop. Most individuals available in the trade are wild-caught, so a new arrival should be given time, cover and low disturbance to settle in.
Conservation
Polypterus congicus is assessed as Least Concern on the IUCN Red List, per the 2022 assessment, with no immediate species-wide conservation concerns identified and populations reported as stable and widespread across the Congo basin. It is one of the more secure bichirs, benefiting from the sheer scale of the Congo drainage it inhabits.
That said, most individuals reaching the aquarium trade are still wild-caught rather than captive-bred, unlike the farm-raised Senegal bichir, so the ornamental fishery represents an ongoing, if currently unquantified, draw on wild populations. Given the species' Least Concern status, that trade does not currently appear to threaten it at the population level, but its very large adult size and continued reliance on wild collection make it a fish best sourced thoughtfully.