Taxonomy & naming
Leporinus arcus was described by the American ichthyologist Carl H. Eigenmann in 1912, from material collected at Tukeit, Guyana, which stands as the species' type locality. It belongs to the family Anostomidae — the headstanders — within the order Characiformes, a family whose members are named for their distinctive habit of feeding at a steep, head-down angle rather than for any anatomical "standing" structure. The genus Leporinus is large and taxonomically active, and species-level identification within it is frequently difficult without close comparison of banding pattern, body depth and fin coloration, so aquarium-trade identifications of Leporinus species should be treated with some caution.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the standing authority for the valid name and combination; this article follows that placement and the genus Leporinus as given, without reassignment. The common name "lipstick leporinus" refers to the reddish or orange mark that some individuals show around the mouth, distinguishing the species by eye from other yellow-and-black-banded Leporinus in the trade.
Morphology
Leporinus arcus has the classic headstander silhouette shared across the genus: an elongated, slightly compressed, torpedo-like body with a small, underslung mouth set for grazing rather than grasping prey, and a tail and dorsal fin proportioned for quick bursts of swimming. FishBase records a maximum size around 15.5 in, and aquarium-trade sources consistently describe adults in the 12–15.5 in range — a genuinely large characin, not a nano or small community fish, and considerably bigger than the banded Leporinus species most casually sold as juveniles.
Colouration follows the typical Leporinus pattern of dark vertical or diagonal bars over a pale, silvery-yellow body, with the "lipstick" common name pointing to a reddish tinge around the mouth in some individuals. As with many Leporinus, juveniles and adults can differ somewhat in banding intensity and body depth, and colour can shift with mood and social standing within a group.
Habitat
The species is native to the coastal river systems of the Guianas and Venezuela and extends into the upper Amazon basin, occupying benthopelagic freshwater habitats — it associates closely with the river bottom and submerged structure rather than the open water column. Within these systems it grazes over wood, rock and sediment surfaces where algae and biofilm accumulate, consistent with the head-down feeding posture that gives headstanders their name.
Water across its range runs warmer tropical to a touch cooler than many Amazonian blackwater characins: aquarium-care sources report a workable range of roughly 68–82 °F and pH 6-7.5, spanning mildly acidic to neutral conditions rather than extreme soft blackwater. Data on the specific hydrology of its home rivers is otherwise sparse in the available sources.
Feeding
Leporinus arcus is a benthic omnivore and aufwuchs grazer: in the wild it feeds on algae, small invertebrates and organic detritus picked from submerged surfaces while angled head-down, the classic headstander foraging posture. This grazing habit means the species also readily browses soft aquarium plants, and keepers should expect some plant damage unless tough, unpalatable species are used.
In the aquarium it takes a varied diet well: algae-based foods, sinking herbivore/omnivore pellets, blanched vegetables and occasional protein such as small invertebrate-based foods round out a diet that mirrors its natural grazing-plus-opportunistic-feeding habits. A diet skewed too heavily toward meaty protein, with no vegetable matter, does not match what the species eats in the wild.
Mating
Little detail on courtship behaviour specific to Leporinus arcus appears in the available sources. What is documented is that distinct pairs form and spawn among densely grown weedy vegetation, suggesting pairing behaviour with a preference for heavily planted or root-dense spawning sites, broadly consistent with egg-scattering habits reported elsewhere in the genus. Data on external sexual dimorphism, courtship display or specific spawning triggers is sparse and not confirmed by the cache for this species.
Breeding
Leporinus arcus is, per the available sources, an egg-scatterer that spawns in pairs over dense weedy growth in the wild, matching the pattern documented for other Leporinus and Anostomus headstanders, which are rarely bred successfully in the home aquarium. FishBase explicitly notes that aquarium breeding of this species has been unsuccessful, and no parental care is documented — consistent with the scattering, non-guarding mode typical of the group.
Hobbyists should not expect to breed this species at home; it is essentially a wild-collected or farmed import for the trade rather than a captive-bred aquarium fish, and prospective keepers should set expectations accordingly.
In the aquarium
The headline fact for any keeper is size and temperament: Leporinus arcus grows to 12–15.5 in and needs a genuinely large aquarium — trade sources suggest at least 160 US gal for a small group of five to six fish — with strong filtration and open swimming space along with structure to graze on. This is not a fish for a standard community tank sized for small tetras.
Socially, the species establishes a hierarchy among similarly sized individuals, and that process involves real aggression: equal-sized tankmates may fight intensely at first, though most accounts describe the group settling into peaceful coexistence once the pecking order is established. Like many of its Leporinus and Anostomus relatives, it has a real reputation as a fin-nipper, particularly toward slower or long-finned tankmates, so stocking should favour robust, fast, similarly sized fish — hobbyist accounts describe it as comparatively less consistently aggressive than true Anostomus headstanders, but still capable of nipping. It has also been kept successfully alongside larger South American cichlids. Because it browses soft vegetation, keepers wanting live plants should choose tough, unpalatable species. As with all large characins, never assume a juvenile's mild manners will hold once it reaches adult size.
Conservation
Leporinus arcus is assessed by the IUCN Red List as Least Concern. The species has a reasonably wide native range across the coastal rivers of the Guianas, Venezuela and the upper Amazon, and the available sources do not document any significant population decline or targeted conservation concern. Detailed population trend data and specific threats within its range are not covered in the available sources, so this account does not speculate beyond the Least Concern assessment.