Taxonomy & naming
Dianema urostriatum was first described by the Brazilian ichthyologist Alipio de Miranda Ribeiro in 1912 under the original combination Decapogon urostriatum, with the type locality given as Manaus, Amazonas, Brazil. The species was later placed in the genus Dianema, where it now resides as the valid name under the Catalog of Fishes (Eschmeyer, California Academy of Sciences). The family Callichthyidae — the armoured callichthyid catfishes — sits within the diverse order Siluriformes.
The genus Dianema is small: a 2025 mitochondrial genomic study confirmed that the genus contains exactly two valid species, D. urostriatum and D. longibarbis (Cope, 1872), the porthole catfish. The two can be distinguished readily by tail pattern: D. urostriatum carries bold horizontal black and white stripes on the caudal fin, while D. longibarbis has a plainer tail and longer barbels.
Morphology
The flagtail catfish has a moderately elongated, somewhat laterally compressed body covered in two rows of overlapping bony scutes (plates), giving it the armoured texture typical of the family. The head is flat and broad, with a downward-slanting mouth and several pairs of short barbels. The dorsal fin is tall, the adipose fin long and low, and the caudal fin is forked and boldly patterned with alternating horizontal black and white stripes — the feature that gives the species its common name.
Adult standard length reaches about 5 in; aquarium specimens are commonly 4–4.5 in. As in all callichthyids the body lacks true scales, the skin instead being covered by the bony scute rows, but this still qualifies as a scaleless fish for medication purposes, demanding conservative copper and chemical treatment. The pectoral fins carry stiff, locking spines that can tangle in a net and jab the handler; the fish should always be moved in a container rather than netted.
Habitat
Dianema urostriatum is native to the Amazon basin of Brazil, with the type locality at Manaus, the confluence of the Rio Negro and the Amazon proper in Amazonas state. It inhabits slow to gently flowing rivers and flooded flats, typically in soft, slightly acidic to neutral water with abundant vegetation, leaf litter and submerged wood.
Water conditions in the Rio Negro tributaries and Amazon floodplain where this species is recorded are typically warm (77–82 °F), soft to moderately hard (roughly 5–19 dH) and neutral to slightly acidic (pH 6.0–8.0, with the lower end of that range being more representative of its typical habitat). It is not a fast-water fish and prefers calm sections with cover.
Feeding
Dianema urostriatum is an omnivore that forages primarily over the substrate and in the water column at night. In nature it takes small aquatic invertebrates, detritus, worms, daphnia and other microorganisms, with some plant material included opportunistically.
In the aquarium it accepts a varied diet without difficulty: quality sinking catfish pellets and wafers form a solid base, supplemented with frozen or live bloodworm, brine shrimp, daphnia and chopped earthworms. Like most callichthyids it is more active after dark, so feeding once lights are off ensures it is not consistently out-competed by diurnal tankmates.
Mating
As an armoured callichthyid in the Dianema lineage, D. urostriatum follows the bubble-nest breeding strategy shared by its relatives Hoplosternum, Megalechis and Callichthys. The male initiates construction of a floating bubble-nest, typically positioned at the surface beneath a broad floating leaf, overhanging vegetation or any available cover. He blows and maintains a raft of mucus-coated bubbles using air gulped from the surface — a behaviour that also reflects the genus's capacity for aerial respiration.
Conditioning with copious live or frozen food is generally necessary to bring fish into breeding condition. Females that are ready will be visibly fuller-bodied than males. Despite being documented as a bubble-nest builder in the aquarium literature, confirmed captive spawning records remain sparse, and the species appears to require very specific conditions including abundant live food and appropriate cover.
Breeding
When breeding occurs, the male constructs the floating bubble-nest and the female deposits her eggs into it after courtship. The male then guards the nest, aerating and tending it, and defends the site against intruders. This is the standard callichthyid pattern seen in Hoplosternum littorale and related species.
In practice, captive breeding of D. urostriatum is not well documented and is reported as difficult. Seriously Fish notes bubble-nest construction has been recorded but confirmed home-aquarium breeding is uncommon; ScotCat considers breeding undocumented in captivity. The difficulty appears to relate to conditioning requirements: the fish demands very generous provisioning with live food, appropriate spawning triggers (often a period of cooler or more oxygenated water to simulate seasonal conditions), and peaceful surroundings. A dedicated breeding setup with a group of fish and floating cork bark or broad-leaved plants offers the best chance.
In the aquarium
Dianema urostriatum is a peaceful, sociable species that does best kept in a group of at least four to six individuals; solitary specimens are shyer and less active. A tank of 47 in or more suits a group of adults comfortably. Provide dense planting, floating plants or cork bark at the surface, driftwood and leaf litter for cover, and a fine sand substrate — the fish will browse and forage across it throughout the night.
Water should be soft to moderately hard (5–19 dH), slightly acidic to neutral (pH 6.0–8.0, leaning toward the lower end in practice) and warm (77–82 °F). It is scaleless, meaning copper and many common medications must be dosed conservatively to avoid toxicity — treat at half the standard dose or use copper-free alternatives where possible. The pectoral spines lock firmly when the fish is alarmed, catching in net mesh and capable of piercing skin; always move it in a container. It is compatible with most peaceful community fish that are too large to threaten it but it is best not combined with boisterous or nippy species that would stress a slow-moving, nocturnal catfish.
Lifespan in good conditions is reported at eight to ten years, so a kept group represents a real commitment; provide stable water quality and consistent feeding for long-term success.
Conservation
Dianema urostriatum is assessed as Least Concern on the IUCN Red List. The species is distributed across the Amazon basin of Brazil, a broadly continuous range, and faces no currently identified specific threat that would justify a higher category.
As with most Amazon basin fish, long-term pressures include deforestation and the resulting siltation of river systems, hydroelectric development, and degradation of floodplain habitats. The aquarium trade draws on wild-caught individuals from the Amazon region; improving captive-breeding success in the hobby would reduce collection pressure on wild populations. The species is not known to be subject to commercial food fishery.