Taxonomy & naming
Leporinus cylindriformis was described by the Russian-American ichthyologist Nicholas Borodin in 1929. It belongs to the family Anostomidae, the headstanders, within the order Characiformes, and to the genus Leporinus, one of the largest genera in that family and one whose species are frequently confused with one another and with the related genus Anostomus on the basis of body shape and banding pattern alone.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid name and combination; this article follows that placement and keeps the species in Leporinus. As with many Leporinus species, identification within the genus can be difficult without close examination of meristic counts and colour pattern, and older literature or trade listings may apply names loosely; this account treats only what can be attributed to L. cylindriformis specifically. The genus name Leporinus derives from the Latin lepus ("hare"), an old allusion to the fish's protruding, rabbit-like incisor teeth used for grazing.
Morphology
Leporinus cylindriformis has the characteristic headstander build shared across the genus: an elongate, sub-cylindrical body (reflected in the species name cylindriformis, "cylinder-shaped"), a small terminal-to-slightly-inferior mouth set with the chisel-like incisors typical of Leporinus, and a single dorsal fin set well forward of the adipose fin. FishBase records a maximum published length of 8 in standard length, a modest size for the genus, some of whose members exceed 12 in.
Colour pattern in Leporinus generally consists of dark bars or blotches over a pale silvery-to-golden ground colour, though the cache consulted for this account did not capture a detailed pattern description specific to L. cylindriformis; keepers should expect the general Leporinus look — a slender, laterally compact body built for holding position in current — rather than assume a specific banding pattern without a photographic reference. No reliable external sexual dimorphism is documented for this species.
Habitat
Leporinus cylindriformis is native to South America, recorded from the lower Amazon River basin in Brazil. It is described as benthopelagic, occupying the water column just above the bottom, consistent with its head-down grazing habit over submerged wood, rocks and leaf litter in flowing or slow-moving freshwater.
Specific water chemistry data for this species was not captured in the available sources; as a lower-Amazon-basin fish it can be expected to encounter the region's typically warm, soft-to-moderate, mildly acidic-to-neutral water, but keepers should treat precise pH and hardness figures as unconfirmed for this species rather than assume the extremes sometimes cited for blackwater specialists.
Feeding
Leporinus cylindriformis is an omnivore with a strong lean toward grazing, reflected in FishBase's trophic level of 2.4 for the species — closer to a herbivore/detritivore than a predator. In the wild it grazes algae, biofilm and plant material from submerged surfaces in its head-down posture, supplementing this with small invertebrates such as insects, worms and crustaceans.
In the aquarium, related Leporinus species are fed a diet built around vegetable matter — algae wafers, blanched vegetables such as lettuce, courgette and peas, and spirulina-based foods — alongside occasional meaty foods like bloodworm or brine shrimp to round out the diet. This species should be fed the same way: a vegetable-forward diet with modest protein supplementation, not a carnivore-style regime.
Mating
FishBase describes Leporinus cylindriformis as forming distinct pairs that breed in densely vegetated, weedy areas, which is consistent with the pair-spawning behaviour documented across the genus. Beyond that, the available sources do not describe courtship behaviour, conditioning triggers, or how sexes are distinguished for this species; data is sparse, and no dimorphism has been documented.
Breeding
Headstanders in the genus Leporinus are, as a group, egg-scatterers with no parental care, and reports of successful captive breeding are rare — a handful of Leporinus and the closely related Anostomus have spawned in well-planted aquaria, and some Leporinus species are produced on a small farmed scale for the trade, but this is not a group that breeds reliably or predictably at home. FishBase's note that L. cylindriformis pairs breed in densely grown weedy places points to a scattering spawn over or among fine-leaved vegetation, similar to its relatives, but no detailed spawning account for this specific species was found in the sources consulted.
Prospective breeders should treat L. cylindriformis as essentially unbred in the hobby: honest expectations matter more here than optimism, and eggs, if produced, would receive no parental care and should be assumed vulnerable to predation by the parents and any tankmates unless removed.
In the aquarium
At a documented maximum of 8 in SL, Leporinus cylindriformis is a mid-sized characin that needs a long, well-filtered aquarium with open swimming space and strong water movement to reflect its riverine, benthopelagic habits — a tank in the range suggested for similarly sized Leporinus (roughly 200+ litres) is a reasonable starting point, sized up as the fish grows. Décor should include driftwood and smooth stones for it to graze over, along with tough or fast-growing plants, since soft-leaved species are likely to be sampled or shredded.
As with many Leporinus and Anostomus species, individuals can become territorial and nippy as they mature, particularly toward slow-moving or long-finned tankmates; this is a genus-wide honest hook, not a guarantee for every individual, but keepers should plan tankmates and stocking density with that risk in mind. Feed a vegetable-forward diet (see Feeding) and expect an active, hardy, if unspectacular, grazing characin rather than a centrepiece fish.
Conservation
Leporinus cylindriformis is assessed by the IUCN Red List as Least Concern, though the sources consulted did not capture a specific assessment year or numeric ID for that listing. As a lower-Amazon-basin species without an unusually restricted range noted in the available literature, it does not appear to face the acute, localised pressures that threaten single-river or single-lake endemics elsewhere in South America, though the general pressures on Amazonian freshwater habitats — deforestation, damming and water-quality change — remain relevant long-term watch items for the basin as a whole.