Taxonomy & naming
Vandellia cirrhosa was described by the French zoologist Achille Valenciennes in 1846, the species epithet cirrhosa referring to the small cirri (barbel-like projections) on the head. The genus Vandellia belongs to the family Trichomycteridae, the parasitic and pencil catfishes of South America — a diverse, largely small-bodied family distributed across rivers from Trinidad south to Patagonia. Within Trichomycteridae the subfamily Vandelliinae contains the blood-feeding candirus, of which Vandellia is the best-known genus. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Vandellia cirrhosa as the valid name.
Several other small trichomycterids share the vernacular name "candiru", and published accounts sometimes conflate Vandellia cirrhosa with related genera such as Paravandelia or Branchioica. The taxonomy of the group has been revised periodically and remains an active area of ichthyological research; readers should treat any older combination not using the genus Vandellia with caution.
Morphology
Vandellia cirrhosa is a tiny, almost eel-like catfish, reaching only about 1 in standard length at maturity. The body is elongate and laterally compressed, nearly translucent in life, and entirely scaleless — the naked skin gives it no armour and renders it acutely sensitive to dissolved copper and many other medications. Short, stout spines on the operculum (gill cover) and a body surface studded with small retrorse (backward-pointing) hooks allow the fish to anchor itself inside the gill chamber of a host, resisting removal; these are not the locking pectoral spines of armoured catfish but a different set of anchoring structures.
Barbels are short and inconspicuous. The mouth is small and positioned to abrade gill tissue. Because the fish is so small and nearly translucent when alive, it can be difficult to spot against a dark substrate.
Habitat
Vandellia cirrhosa is native to the Amazon and Orinoco river systems of South America, occupying slow-flowing and still waters — river channels, floodplain lakes (várzea and igapó), and backwaters — across a broad range that includes Brazil, Colombia, Peru, Venezuela, and neighbouring countries in the basins. It inhabits warm, soft, often blackwater environments: temperatures in the range of 72–79 °F and pH typically 5.5–7.0, with low conductivity characteristic of the Amazonian lowlands.
Benthic in habit, it is most active after dark and spends much of its time concealed in soft substrate or leaf litter. In the wild it locates larger fish hosts by detecting the ammonia trail of their gill outflow, then swims rapidly into the gill chamber to feed.
Feeding
The feeding biology of Vandellia cirrhosa is genuinely unusual. It is a facultative gill-parasite: it enters the gill chambers of larger fish (particularly large characids, catfishes, and reportedly other vertebrates) and uses its small, sharp teeth to abrade the gill filaments and feed on blood. This is a rapid, opportunistic raid rather than a permanent attachment; after feeding the fish withdraws and resumes free-living behaviour.
In captivity, if the fish is ever held, it would need to be provided with appropriate food sources. In practice it is essentially unknown in the aquarium trade, and there is no established protocol for feeding it outside of its natural host context. The diet is therefore best described as haematophagous (blood-feeding), at least in its semi-parasitic phase; whether free-living individuals supplement this with detritus or small invertebrates is not well documented.
Mating
Mating behaviour in Vandellia cirrhosa has not been described in the scientific literature in any detail and is unknown in aquarium conditions. No observations of courtship, pairing, or spawning have been published for this species. Given the biology of the wider family Trichomycteridae — in which some species are benthic egg-scatterers with little parental involvement and others have unknown reproductive modes — it would be speculative to assign a specific mating strategy here.
Data on sexual dimorphism are also sparse; no reliable external characters for sexing live fish have been confirmed in the literature.
Breeding
There is no record of Vandellia cirrhosa being bred in home aquaria, and it is effectively impossible to breed in a home setting. The species is almost never available in the trade, its minute size and specialised biology make conventional aquarium husbandry impractical, and no protocols exist for inducing or documenting spawning. Aquarium breeding must be considered unknown and, in practice, not achievable under hobby conditions.
For completeness, the reproductive mode for the species is presumed to involve egg-laying of some form, as is typical for most small trichomycterids, but this has not been confirmed with observations. No parental care behaviour is documented.
In the aquarium
Vandellia cirrhosa is not a practical aquarium fish and is essentially absent from the trade. It is included here as part of an exhaustive account of catfishes rather than as a recommendation. If somehow obtained, it would require warm (72–79 °F), soft (pH 5.5–7.0), well-oxygenated blackwater conditions and a fine, dark substrate with leaf litter for cover; all of this is straightforward enough, but the semi-parasitic feeding mode poses a severe practical problem — the fish needs access to larger host fish to feed, and providing live hosts is neither ethical nor feasible in most home aquaria.
Because it is entirely scaleless, Vandellia cirrhosa is acutely sensitive to copper-based treatments and many antiparasitic medications; should any treatment ever be necessary, a conservative half-dose or a copper-free alternative is essential. The fish carries small but effective opercular spines and body hooks that can catch on soft material — it should not be handled directly. Its minute size makes it vulnerable to predation by any tankmate larger than itself. In summary: this fish belongs in a specialist research context rather than a home aquarium.
Conservation
Vandellia cirrhosa has not been assessed by the IUCN Red List and is currently listed as Not Evaluated. It is a broadly distributed species across the Amazon and Orinoco basins — among the largest river systems on Earth — and is not specifically targeted by fisheries or the ornamental trade.
The primary long-term threats, as for most Amazonian freshwater fish, are deforestation and habitat degradation leading to sedimentation, altered hydrology, and water quality changes in the várzea floodplain lakes it inhabits. Because the species is data-sparse and rarely collected, population trends are effectively unknown. It does not appear in conservation-priority assessments for the region.