Taxonomy & naming
Polypterus weeksii was described by the Belgian-British ichthyologist George Albert Boulenger in 1898, and is placed by the Catalog of Fishes in the genus Polypterus, family Polypteridae, order Polypteriformes — the bichirs and the reedfish, the most basal living lineage of the ray-finned fishes (Actinopterygii). Like every member of the family, it is a true living fossil: a survivor of a branch of the bony fishes that split away from all the others deep in the fossil record and has changed comparatively little since.
The species carries the common name Weeks' bichir or mottled bichir in the trade, and its scientific epithet honours John Henry Weeks (1861–1924), a British Baptist missionary and explorer who worked for decades on the upper Congo River. Boulenger's type specimen was collected at Weeks' own mission station at Monsembe, on the upper Congo in what is now the Democratic Republic of the Congo — one of several Congo basin species named for the missionary-naturalists who supplied European museums with specimens in that era. It is endemic to the Congo basin, recorded only from the Democratic Republic of the Congo and the neighbouring Republic of the Congo.
Morphology
Polypterus weeksii shows the classic bichir body plan: an elongate, cylindrical body sheathed from head to tail in thick, glossy, interlocking ganoid scales — rhombic plates of bone capped with a hard, enamel-like layer — that form a flexible suit of armour. In place of a single dorsal fin it carries a row of separate finlets, each a small spine trailing a membrane flag; FishBase counts nine to eleven of them running from mid-back toward the tail, a useful character for telling the species from its Congo basin relatives. The paired pectoral fins sit on fleshy, muscular lobes that the fish uses to prop itself up and shuffle across the substrate almost like limbs. Colouration is a dark, mottled pattern over a paler body, the mottling behind the common name.
FishBase records a maximum length of 21.3 in total length, making it one of the larger Congo Polypterus species, though aquarium specimens are usually smaller. Like the rest of the family it has poor eyesight and hunts largely by smell, and it breathes air with a pair of primitive lungs connected to the gut, rising to gulp at the surface — a fish denied that access can drown. One trait sets it apart even among bichirs: its larvae retain the feathery external gills behind the head, present in all young Polypterus, for markedly longer than other species in the genus before they are absorbed — a slower developmental clock that hints at its own distinct place within the family.
Habitat
Polypterus weeksii is a Congo basin endemic, recorded from the Democratic Republic of the Congo and the Republic of the Congo, with its type locality at Monsembe on the upper Congo River. Within that range it inhabits the warm, slow-moving lowland stretches typical of Congo basin rivers — channel margins, flooded forest and swampy backwaters — the same tannin-stained, oxygen-poor waters that make an air-breathing lung so valuable to every bichir species that lives in them.
Detailed water-chemistry data from the wild are sparse, but aquarium keepers report the species doing well in warm water around 77–82 °F and a pH from mildly acidic to alkaline (roughly 6.5–8.0), consistent with the broad tolerance typical of the genus, and it appreciates a soft substrate, driftwood and plenty of hiding places that mimic its native cover.
Feeding
Like other bichirs, Polypterus weeksii is a nocturnal, ambush-hunting carnivore with poor eyesight that relies on a keen sense of smell to locate prey on or near the bottom, engulfing it with a fast sideways snap of the jaws once found. In the aquarium it takes a range of meaty foods readily — prawn, earthworm, mussel and small fish such as lancefish — and adapts well to frozen and live foods offered after dark, when it is naturally most active.
It is a messy eater that leaves scraps and produces a significant bio-load for its size, so strong filtration and regular water changes matter more for this species than for many community fish. Because it hunts by scent rather than sight and moves deliberately, it can be out-competed by fast, sighted tankmates at feeding time, and keepers often do best feeding it directly near its hiding spot.
Mating
As in other Polypterus, courtship in P. weeksii is built around a distinctive fin-cupping ritual rather than a nest or territory. The male follows a ripe female and, when spawning begins, curls his thickened anal and pelvic fins into a shallow pouch; the female releases a small batch of eggs into it at a time, and the male fertilises them there before the small, sticky eggs are scattered onto plants and other cover. The sequence repeats over an extended period as more batches are laid.
The clearest external sign of sex in this species, as across the genus, is the male's broader and more muscular anal fin, adapted for cupping the eggs; females tend to be a little larger and heavier-bodied. There is no lasting pair bond and no territory defended before or after spawning.
Breeding
Polypterus weeksii is an egg-scatterer with no parental care whatever: adults take no interest in the eggs or fry they produce and will eat both given the opportunity. The small, adhesive eggs are deposited among aquatic vegetation and hatch quickly, in roughly three to four days, into larvae that — distinctively for this species — carry feathery external gills behind the head for notably longer than the larvae of other Polypterus species before those gills are absorbed and true gill breathing takes over.
Breeding has never been reliably documented in the home aquarium, and spawning in the wild is thought to follow the seasonal flooding of the rainy season across the Congo basin, the same cue believed to trigger reproduction in many of its relatives. As with the large majority of the genus, essentially all Polypterus weeksii available in the aquarium trade are wild-caught rather than captive-bred.
In the aquarium
Polypterus weeksii needs the same commitment as any large bichir. Aquarium sources recommend a minimum of around 100 gallons (roughly 100 US gal) for an adult, furnished with soft substrate, driftwood and enough hiding places that the fish can retreat by day, since it is a nocturnal hunter with poor eyesight. As with every bichir, a completely tight-fitting lid is non-negotiable — this is a determined escape artist capable of pushing through the smallest gap, and a fish found dried out on the floor is the most common way keepers lose one — while still leaving an air gap at the surface for it to breathe.
It is unsuitable for a small-fish or nano community: anything it can fit in its mouth is at risk. It does best alongside similarly large, robust tankmates — other Polypterus, larger Synodontis catfish, Ctenopoma bushfish, or medium-to-large characins — that are too big to eat and unlikely to harass a slow-moving, scent-hunting predator. Its diet of prawn, earthworm, mussel and small fish, combined with its messy feeding habits, calls for strong filtration and a keeper prepared for a large, long-term bio-load.
Conservation
Polypterus weeksii is assessed as Least Concern on the IUCN Red List, an assessment made in 2009 and published in 2010. The species is described as widespread across the central Congo River basin, and the assessment identifies no major threats to its populations.
Its security, like that of many Congo basin fish, rests on the general health of the basin's rivers and floodplain forests; the ornamental trade takes little pressure off wild populations, since most fish in the hobby remain wild-caught rather than farmed, unlike the more commercially bred Senegal bichir. No targeted conservation measures are known to be in place, and none currently appear necessary given its wide range and stable status.