Taxonomy & naming
Microglanis nigripinnis was described by Bizerril & Perez-Neto in 1992. It belongs to the family Pseudopimelodidae, the bumblebee and dwarf pimelodid catfishes, a group that was historically lumped into Pimelodidae before being split out as its own family. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Microglanis nigripinnis as the valid combination and the governing authority for the name.
The genus name Microglanis combines the Greek mikros ("small") with glanis, an old name for a catfish, describing the genus's generally diminutive size compared to other pimelodid-type catfishes. The species epithet nigripinnis is Latin, from niger ("black") and pinna ("fin"), referring to dark pigmentation on the fins. As with much of Siluriformes, the family-level placement of small South American catfishes like this one has shifted with revision; aquarists may still see it grouped loosely with other "bumblebee catfish" regardless of exact family.
Morphology
This is a small, robust little catfish with the classic pimelodid-type profile: a broad, flattened head, three pairs of long, sensitive barbels used to locate food in the dark, and a stout, scaleless body. Like other Microglanis it typically shows a mottled or blotched pattern of dark brown to black over a pale yellowish-brown ground colour, though the exact patterning is variable between individuals.
Microglanis nigripinnis is one of the smallest species in its genus, reaching a maximum size of only about 2 in standard length. That places it firmly among the dwarf catfishes of the hobby — considerably smaller than the more familiar Microglanis iheringi, the bumblebee catfish commonly sold in the aquarium trade, with which it and other small Microglanis are frequently confused or mislabelled. As in all catfishes in this group, the skin carries no scales, which matters for medication dosing (see "In the aquarium").
Habitat
Microglanis nigripinnis is known from the Rio Macacu basin, a system of small coastal rivers draining to the sea near Rio de Janeiro in southeastern Brazil. It occupies slow-flowing sections of these rivers rather than fast, well-oxygenated riffles, sheltering by day among cover such as leaf litter, roots, and submerged debris.
Detailed water chemistry data for the type locality is sparse in the available literature. Coastal Rio de Janeiro streams of this kind are generally warm, soft, and close to neutral to slightly acidic, and aquarium guidance for the genus points to soft, slightly acidic water in the roughly 72–82 °F range as suitable, but exact figures specific to this species should be treated as an approximation rather than a measured record.
Feeding
Microglanis nigripinnis is a nocturnal benthic micro-predator. In the wild it forages along the bottom after dark, using its barbels to detect small aquatic invertebrates — worms, small crustaceans, and insect larvae — and has also been noted taking fish fry at night, a reminder that even a tiny catfish is an opportunistic hunter after dark.
In the aquarium it accepts sinking pellets, frozen foods such as bloodworm and brine shrimp, and other small prepared foods once settled. Because it feeds mainly at night, offering food after the lights go out — or timing a final feed for dusk — helps ensure this shy, small species is not out-competed by more active tankmates for food.
Mating
Specific courtship and spawning behaviour for Microglanis nigripinnis has not been well documented in the available literature. What is reported for the genus in aquarium settings is a non-guarding scatter spawn: pairs release eggs over or among fine-leaved plants or similar cover rather than building a nest, with no evidence of the parental care seen in some other catfish groups (such as the bubble-nesting armoured Callichthyidae or the internally fertilising driftwood catfishes).
Breeding in home aquaria is reported as rarely practiced for the genus, and soft, slightly acidic water is suggested as a trigger or requirement when spawning has been achieved. Data specific to this species' own mating behaviour is sparse — treat genus-level accounts as a guide rather than a confirmed description of M. nigripinnis itself.
Breeding
As with mating, dedicated breeding accounts for Microglanis nigripinnis specifically are scarce. The genus is reported to spawn occasionally in captivity via non-guarding egg-scattering onto plants, in soft, slightly acidic water around 72–82 °F, but successful home breeding is uncommon and not a reliable expectation for hobbyists.
No parental care beyond releasing the eggs has been reported for this genus — unlike some catfish families that guard a nest or brood site, Microglanis appears to leave the eggs and any resulting fry to fend for themselves. Anyone attempting to breed this species should expect low, inconsistent success and should not assume any brooding or guarding behaviour will occur.
In the aquarium
Microglanis nigripinnis is a genuine dwarf catfish — its real adult size tops out around 2 in — so, unlike many larger "bumblebee catfish" sold under similar names, it does not carry the size-trap risk of outgrowing a small tank. It nonetheless needs a tank with soft substrate, plenty of cover (roots, leaf litter, small caves), and dim lighting or floating plants, since it is nocturnal and hides through the day.
Being scaleless, it is medication-sensitive like other naked-skinned catfishes: dose copper-based treatments and many standard medications conservatively, often at reduced strength, and monitor closely. It is described as peaceful and sociable with its own kind and with other fish, making it a good candidate for a quiet nano community, though its nocturnal, fry-eating habits mean very small or very young tankmates are not entirely safe overnight. Feed after lights-out to make sure it gets its share.
Conservation
The IUCN Red List assesses Microglanis nigripinnis as Data Deficient, reflecting how little is known about its population size, trend, and the extent of threats across its range. The assessment dates to 7 November 2018.
The species is known only from the Rio Macacu basin and other small coastal rivers of Rio de Janeiro State, a heavily populated and developed part of Brazil where coastal streams face pressure from urbanisation, pollution, and habitat modification. With no population data available, the precautionary approach is to treat the species as potentially vulnerable to local habitat pressures until better information exists, and to avoid over-collection from what appears to be a narrow native range.