Taxonomy & naming
Microglanis poecilus was described by the American ichthyologist Carl H. Eigenmann in 1912. It belongs to the family Pseudopimelodidae, the bumblebee catfishes and their relatives, a group that was long lumped into Pimelodidae before being split out on its own; older literature and some aquarium references may still list Microglanis species under the broader "Pimelodidae" umbrella. The Catalog of Fishes treats Microglanis poecilus as the currently valid name, within the genus Microglanis, which comprises a couple of dozen small South American catfishes commonly traded as "bumblebee catfish" (a name more properly tied to Microglanis species with bold black-and-yellow banding).
The genus name Microglanis combines Greek mikros, "small", with glanis, an old name for a catfish — a fitting label for a genus whose members rarely exceed a few centimetres. The species epithet poecilus is Greek for "variegated" or "spotted", referring to the mottled, marbled colour pattern that gives the fish its common name.
Morphology
This is a genuinely tiny catfish: maximum recorded size is about 3 in standard length, with some sources giving a slightly smaller 2.5 in, making it one of the smallest species in its family. The body follows the typical pseudopimelodid plan — a broad, somewhat flattened head, a stout body tapering to the tail, and long barbels used to feel out food and obstacles in the dark. As in other catfish the skin carries no scales, which is worth remembering when treating disease (see "In the aquarium").
Colouration is a mottled, marbled mix of browns and creams over the body, giving strong camouflage against a leaf-litter substrate. A single pectoral spine is present on each side with a pointed tip; sources describe it as non-venomous in this species, though as with any catfish spine it can still snag a net or jab a careless hand and is best respected. Sexual dimorphism is minimal and not reliably documented for external sexing.
Habitat
Microglanis poecilus is native to South America, recorded from the Essequibo River basin and river systems of French Guiana; the type locality is given as below Packeoo Falls in what was then British Guiana (now Guyana). It lives in creeks with little current, on bottoms covered in decomposing leaf litter — a classic leaf-litter microhabitat shared with many small Guiana Shield fishes.
Water in these habitats tends to be soft and slightly acidic, though the species is reported as tolerant: aquarium sources describe it as undemanding enough to do well even in ordinary tap water, with softer, slightly acidic conditions recommended mainly as a spawning trigger rather than a day-to-day requirement.
Feeding
Microglanis poecilus is a nocturnal benthic omnivore, foraging over the bottom after dark for small invertebrates and organic material among the leaf litter. In the aquarium it takes a varied diet without fuss: sinking tablets and pellets, chopped or whole worms, and frozen bloodworm are all reported to be readily accepted.
Because it feeds mainly at night, offering food after the lights go out — or making sure some sinks to its hiding spots — helps it compete with more active, diurnal tankmates. A balanced, varied diet including some live or frozen foods alongside prepared foods keeps it in good condition.
Mating
In the wild, Microglanis poecilus is reported to reproduce during the rainy season, when adults migrate into seasonally flooded areas and spawn over aquatic plants. This is an open-water, broadcast-scattering style of spawning with no reported nest building or brood care — eggs are released among vegetation and left to develop unguarded, in contrast to the cavity-spawning or mouth-brooding strategies seen in some other catfish families.
Because this seasonal flood-plain spawning is difficult to replicate in a home aquarium, courtship and mating behaviour for this species remain poorly documented from captive observation.
Breeding
Breeding of Microglanis poecilus in captivity is rare and poorly documented — sources describe it as essentially unrecorded in the aquarium hobby. What is known points to an open-water egg-scattering strategy tied to the rainy-season flood pulse, with no parental care, rather than any of the nest-building or mouth-brooding modes seen in other catfish groups.
Aquarists wishing to attempt breeding are advised that softer, slightly acidic water may help trigger spawning, mimicking the seasonal conditions of its native creeks, but there is no established, repeatable home protocol for this species. As with many small, obscure South American catfish, most individuals in the trade are wild-collected rather than captive-bred.
In the aquarium
Its true adult size of only around 3 in makes Microglanis poecilus one of the few catfish genuinely suited to a modest nano or small community tank — there is no size trap here, but tank mates should still be chosen with care, since even a small catfish will eat anything smaller that fits in its mouth. Water is reported as undemanding, tolerating ordinary tap water, though a temperature of 70–77 °F and pH 6.0–7.5 sits well within its comfort range.
Provide plenty of hiding places — rockwork, driftwood and dense planting — since this is a nocturnal, secretive fish that shelters by day and emerges to forage after dark. As with any scaleless catfish it is more sensitive than scaled fish to copper-based medications and should be dosed conservatively when treating disease. It is described as peaceful and sociable with similarly sized fish, making it a good choice for a quiet community aquarium rather than anything boisterous.
Conservation
The IUCN Red List currently assesses Microglanis poecilus as Least Concern. It occupies a reasonably wide range across Essequibo basin creeks and river systems in French Guiana, an area with comparatively low habitat pressure by South American standards.
As with many small, little-studied Guiana Shield fishes, detailed population data are sparse, and the species' status should be understood as a general reflection of its range rather than close monitoring. The trade appears to rely on wild-collected fish given the near-total absence of captive breeding reports.