Taxonomy & naming
Dianema longibarbis was described by the American palaeontologist and ichthyologist Edward Drinker Cope in 1872 from the Río Ambyiacu in Peru, a tributary of the upper Amazon. It belongs to the family Callichthyidae — the armoured catfishes — and to the subfamily Callichthyinae, the group that includes the bubble-nest builders Hoplosternum, Megalechis, Callichthys, and the closely related Dianema urostriata. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Dianema longibarbis as the valid name. The genus Dianema is small, holding only two species.
In older literature the species has appeared under different generic placements as the callichthyid classification was refined, but Dianema has been stable for decades and is confirmed by the current Catalog. No synonyms are in common use.
Morphology
The porthole catfish has a slender, laterally compressed body covered in two rows of overlapping bony scutes along each flank — the hallmark of the Callichthyidae. It lacks true scales entirely. The head is moderately flattened, the mouth inferior, and the most conspicuous feature is the elongated maxillary barbels that extend well past the pectoral-fin base and give the species its specific epithet. A second, shorter pair of mandibular barbels completes the sensory array.
Adult size is around 4 in standard length (approximately 3–4 in total length in the trade). The dorsal fin carries a stout, serrated locking spine. The pectoral fins likewise bear locking spines — not reported as venomous, but capable of tangling in a net and jabbing the keeper's hand. Coloration is typically pale buff to grey-brown with rows of small dark spots arranged to suggest portholes along the flanks, matching the trade name.
Habitat
Dianema longibarbis is native to the Amazon basin of Peru and Brazil. Its type locality is the Río Ambyiacu in Loreto, Peru, and its range extends through lowland Amazonian tributaries, both white-water and clear-water systems.
It inhabits warm, soft-to-neutral freshwater: water temperatures of 75–82 °F, pH 5.5–7.5, and hardness in the range of 1–20 dH are consistent with the Amazon lowland profile and with aquarium literature compiled from SeriouslyFish and related sources. The species is a benthic catfish of slow to moderate current, found over silty and leaf-littered substrates where it forages after dark.
Feeding
Dianema longibarbis is a nocturnal benthic omnivore. In the wild it forages over the bottom after dark, picking up invertebrates, detritus, organic particles, and small organic matter from the substrate. The long barbels are sensory aids for locating food in low-light or turbid conditions.
In the aquarium it accepts sinking pellets and wafers, frozen foods such as bloodworm, daphnia and brine shrimp, and prepared carnivore diets. Because it is largely inactive during daylight, it should be fed after lights-out so it is not out-competed by faster-moving tankmates. Live foods condition breeding fish effectively.
Mating
Dianema longibarbis, as a callichthyine catfish, reproduces through bubble-nest spawning — a mode shared with Hoplosternum, Megalechis and Callichthys. The male is responsible for nest construction: he blows a raft of mucus-bound bubbles at the water surface, often beneath a broad floating leaf or a positioned cork tile, creating a stable platform for the eggs.
Conditioning is achieved by feeding heavily on live and frozen foods over several weeks, followed by a simulated dry-season period of slightly cooler, softer water, then a simulated flood-pulse of warmer, clean soft water. This temperature and chemistry shift typically triggers spawning. Females become noticeably rounder with eggs when in breeding condition, providing the most reliable means of sexing the fish.
Breeding
At spawning the pair embraces in a typical callichthyine manner; the eggs are collected by the female and placed into the bubble-nest, which the male subsequently guards and tends, repairing the nest as needed. Clutch sizes are moderate. The male should not be disturbed once guarding; he will maintain the nest until the fry are free-swimming, at which point the parents can be removed.
The fry are small and best started on infusoria or commercial fry food, progressing to microworms and finely crushed flake. Water quality must be high during the rearing period. Dianema longibarbis is genuinely breedable in a home aquarium with appropriate conditioning — unlike many catfish that require hormone induction or commercial facilities. This makes it a rewarding species for hobbyists willing to invest in a separate breeding setup.
In the aquarium
Dianema longibarbis is a peaceful, sociable species best kept in groups of three or more. It is well-suited to a community of similarly-sized, soft-to-neutral-water South American fishes — tetras, other callichthyids, small cichlids — and is undemanding once established. A tank of 20 US gal or more with soft substrate (fine sand preferred over gravel), dim lighting, and plenty of leaf litter or cave cover suits it well. It is most active in the evening and after lights-out.
Two points from its biology apply directly to care. First, it is armoured with bony scutes but lacks true scales, and like all scaleless catfish it is more sensitive to copper-based medications, salt, and certain other treatments than scaled fish — dose conservatively and always check medication suitability for catfish before treating the tank. Second, the locking pectoral and dorsal spines can tangle badly in a net and inflict a painful jab; the fish is best moved using a container rather than a net. It is not reported venomous, but the mechanical wound from a spine should be treated as any puncture wound.
Longevity can exceed 10 years under good conditions. The species adjusts readily to aquarium life and has been in the hobby for many decades, with a modest but steady following among catfish enthusiasts.
Conservation
Dianema longibarbis has not been formally evaluated by the IUCN Red List and carries the status Not Evaluated (NE). No formal Red List assessment has been located for this species.
As an Amazonian lowland fish with a distribution spanning Peru and Brazil, it falls within one of the world's most biodiverse freshwater systems. General pressures on Amazonian fish communities — deforestation, sedimentation, and changes in hydrological regimes — are relevant background concerns, though no specific threat data for this species is published. A proportion of the aquarium trade supply is wild-collected from Peruvian Amazonian rivers; captive breeding, while feasible, has not displaced wild collection entirely.