Taxonomy & naming
Leporinus pellegrinii was described by the Austrian ichthyologist Franz Steindachner in 1910 and placed in the genus Leporinus, part of the headstander family Anostomidae within the order Characiformes. The genus name Leporinus is Latin for "hare-like," a reference to the two prominent, forward-projecting incisors in the upper jaw that give the group's mouth a rabbit-like look; the species epithet pellegrinii honours the French ichthyologist Jacques Pellegrin, a prolific describer of Neotropical and African freshwater fishes in the same era.
Anostomidae — the headstanders — is a moderately large family of oblique-swimming, algae-grazing characins found only in South America, and Leporinus is by far its largest genus, with well over 80 recognised species that are frequently confused with one another and with the closely related genus Hypomasticus, into which a number of former Leporinus species have been reassigned by recent revisions. The trade name "Leporinus pellegrini" that circulates in the aquarium hobby is a common orthographic slip of the correctly spelled epithet pellegrinii; this account follows the original, correctly latinised spelling.
Morphology
Leporinus pellegrinii has the elongated, laterally compressed, torpedo-like body typical of the genus, with a pointed head, a small terminal-to-slightly-subterminal mouth armed with the incisor-like teeth that give Leporinus its name, and a forked tail. FishBase records a maximum length of 4.5 in total length, making it one of the smaller members of a genus whose largest species exceed 15.5–19.5 in.
Colouration is silver-gray to dark brown over the flanks, broken by a scatter of irregular black spots and blotches rather than the bold, regular vertical bars seen in some other Leporinus species; the pattern is variable between individuals and can shift somewhat with mood and water conditions. As in other headstanders, the body is built for holding station at a steep, head-down angle while grazing, and the fins are unremarkable — no exaggerated extensions or bright colour markings distinguish this species from its many close relatives.
Habitat
The species is native to the coastal river systems of the Guianas and the upper Amazon River basin, with records extending south into Argentina. Within that range it occupies shallow, calm stretches of rivers and lake margins rather than fast, turbulent water, grazing surfaces exposed to light where algae and biofilm accumulate.
FishBase gives a temperature range of roughly 77–79 °F and pH 5.8–7.5 for the species, while hobby sources report a slightly wider working range of about 75–81 °F and pH 5.9–7.2 — together indicating a warm, soft-to-neutral, mildly acidic to near-neutral freshwater fish typical of Guiana Shield and upper Amazon drainages, without evidence of the extreme blackwater conditions seen in some other Neotropical characins.
Feeding
Leporinus pellegrinii is fundamentally a grazer. FishBase describes it as benthopelagic and herbivorous, feeding on algae and plant material, and hobby accounts confirm an omnivorous-but-primarily-herbivorous diet: the fish uses its pointed incisors to nibble algae and aquatic plants from wood, rock and leaf surfaces, supplementing this with small crustaceans and insects picked up while grazing.
In the aquarium this translates into a need for a genuinely vegetable-forward diet — blanched vegetables, spirulina- or algae-based flake and pellet foods, and driftwood or other grazing surfaces — with occasional protein such as small live or frozen invertebrates. Because it will readily nibble soft-leaved plants when vegetable matter is scarce, keepers who want a planted tank should favour tough, unpalatable species or accept some grazing damage as normal behaviour rather than a diet problem to correct.
Mating
FishBase describes the species as forming distinct pairs in densely vegetated, weedy areas at spawning time, which is the typical pattern reported across small to medium Leporinus species. There is no documented external sexual dimorphism for L. pellegrinii in the available sources, and hobbyists generally identify a compatible pair by behaviour — pairing off and staking out a patch of weed — rather than by colour or fin differences.
A hobby account adds that eggs are laid in summer and hatch within a few days, consistent with a warm-season spawning trigger, but detailed courtship behaviour has not been documented for this particular species and should not be assumed to mirror better-studied Leporinus relatives in every detail.
Breeding
Leporinus pellegrinii is an egg-scattering species with no parental care: FishBase notes that pairs spawn among dense weed growth and does not report any nest-guarding or brood-care behaviour, consistent with the genus as a whole, in which home breeding is rare and most reproduction documented in the literature involves either wild spawning or, in a handful of larger commercial Leporinus species, farmed production rather than deliberate hobbyist breeding.
A hobby source reports that eggs hatch within days of laying and that the resulting fry feed independently on plankton and small crustaceans without parental involvement. Because home breeding reports for this specific species are scarce, keepers hoping to spawn it should treat conditioning in soft, warm, slightly acidic water with dense fine-leaved vegetation as a starting point rather than a guaranteed method, and should not expect any nest defence or fry-guarding behaviour from the adults.
In the aquarium
At a maximum of about 4.5 in, Leporinus pellegrinii is a manageable size for a well-planned community aquarium, and one hobby guide describes it as pleasant and non-aggressive, living well in groups and not preying on smaller tankmates — a notably gentler temperament than the fin-nipping reputation that dogs several larger Leporinus and Anostomus species. That said, it is still an active, oblique-swimming grazer that benefits from a reasonably long tank with open swimming space along with wood and rock surfaces to graze, and keeping it in a small group rather than as a singleton is consistent with the social behaviour reported in the hobby literature.
The most important care point is dietary: this is a grazing herbivore, not an omnivorous scavenger, and a tank without adequate vegetable matter or grazing surfaces will see the fish turn to soft aquarium plants. Keep water warm (roughly 75–81 °F) and soft to neutral (pH around 5.8–7.5), provide driftwood and rock for algae to establish on, and offer vegetable-rich foods regularly. As with any Leporinus, it is worth monitoring behaviour toward slow-moving or long-finned tankmates, since even the comparatively placid species in this genus retain the family's grazing bite.
Conservation
Leporinus pellegrinii has not been formally assessed by the IUCN Red List and is classified here as Not Evaluated. This is a common status for smaller, regionally distributed Neotropical characins that are not major fisheries or trade species; it reflects a lack of dedicated assessment rather than any known population decline.
No specific threats to the species are documented in the sources reviewed for this article. As with other freshwater fish of the Guianas and upper Amazon, the general pressures facing the region — deforestation, mining-related sedimentation and water-quality change, and habitat alteration from damming — are relevant long-term watch items for the rivers it inhabits, even though the species itself carries no current conservation designation.