Taxonomy & naming
Schizodon borellii was described by the Belgian-British ichthyologist George Albert Boulenger in 1900. The species epithet honours Dr Alfredo Borelli (1857–1943), the Italian zoologist and arachnologist whose South American collecting expeditions supplied specimens to European museums around the turn of the twentieth century. It belongs to the family Anostomidae — the headstanders — within the order Characiformes, a family whose members are recognisable across genera (Schizodon, Leporinus, Anostomus, Laemolyta, Pseudanos, Chilodus) for their upturned or downturned grazing mouths and their habit of feeding at an angle to the substrate rather than head-on.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the working authority for the valid genus and combination; nothing in the cited sources suggests any recent generic reshuffling for this species, and it should be treated as Schizodon borellii, not reassigned to Leporinus or any other anostomid genus. GBIF taxonomy confirms Schizodon borellii (Boulenger, 1900) as the valid name in family Anostomidae, distributed through the Paraguay River basin.
Morphology
Schizodon borellii has the typical anostomid build: an elongated, moderately compressed, torpedo-shaped body, a small terminal-to-slightly-subterminal mouth adapted for grazing rather than grabbing, and a plain silvery flank with none of the bold striping seen in some Leporinus and Anostomus species. FishBase records a maximum published length of 14 in for males and 15.5 in for females (total length) — a genuinely large fish for a species so often lumped in casual conversation with small algae-grazers, and one that comfortably outgrows the great majority of home aquaria.
Sexual dimorphism is not well documented for this species beyond the size difference reported by FishBase, with females reaching the larger maximum length; there is no described colour or fin difference distinguishing the sexes.
Habitat
The species is native to the Paraguay River basin, recorded from Argentina and Brazil, where it occupies tropical-to-subtropical freshwater river habitat and is described as benthopelagic — spending time both near the bottom, where it grazes, and in open water within the river channel and its floodplain margins. FishBase gives a maturity length of around 7 in, consistent with a fish that grows well past that size in open river systems.
Because the Paraguay basin at this latitude runs subtropical rather than fully tropical, water temperatures here are cooler on average and more seasonally variable than in equatorial Amazon tributaries; the cache does not report a specific temperature range for this species, and a keeper should treat this as a cooler-running, non-blackwater South American river fish rather than default to warm, soft, acidic Amazon-style parameters without confirmation.
Feeding
Schizodon borellii is a herbivore-leaning omnivore — FishBase records it with a low trophic level (2.4), consistent with a diet dominated by algae, biofilm and plant material rather than animal prey. Like other headstanders, it grazes aufwuchs from submerged wood, rock and other firm surfaces in the characteristic oblique, head-down posture, picking at the same kind of film a plecostomus or an otocinclus targets, but from a considerably larger-bodied fish.
In the aquarium this translates to a diet built around vegetable matter: algae wafers, blanched vegetables, spirulina-based foods and biofilm-rich driftwood, supplemented with a modest amount of prepared or live protein. Soft-leaved aquarium plants are readily eaten by grazing headstanders generally, and a keeper should expect this species to treat tender vegetation as food rather than decor.
Mating
FishBase describes Schizodon borellii as breeding in distinct pairs among densely grown weedy places, indicating a period of pairing off from any larger group before spawning, timed to vegetated microhabitat within the river or floodplain margin. Beyond that pairing behaviour, the cache does not document courtship displays, colour changes or other details of mate selection for this species, and none should be assumed.
Breeding
Schizodon borellii is an egg-scatterer: FishBase reports that pairs spawn in densely vegetated shallows and that there is no parental care of eggs or fry once spawning is complete. This matches the general pattern for headstanders as a group, most of which scatter eggs over or among plants and leave them, in contrast to the substrate-guarding behaviour of true piranhas in the same order.
The species is not documented as a regular aquarium- or farm-bred fish. As with most headstanders, home breeding is rare to essentially unreported; keepers should not expect to reproduce this species in a typical aquarium setup, and any account claiming otherwise should be treated with caution absent a citable source.
In the aquarium
The size on the label matters here: at up to 15.5 in, Schizodon borellii is not a nano algae-eater and needs a large, long aquarium as an adult — closer to the footprint required for a large barb or a mid-sized characin predator than for the small Otocinclus- or Ancistrus-sized grazers hobbyists often associate with algae-eating fish. Tank decor should include driftwood and rock to support natural grazing behaviour, along with tough, grazing-resistant plants (Anubias, Java Fern) rather than soft-leaved species, which this fish and other headstanders will strip.
Headstanders as a group range from placid nano grazers to nippy, territorial adults, and aggression in several genera (notably Leporinus and Anostomus) is strongly reduced by keeping a real group rather than one or two individuals — solitary or lightly-stocked headstanders are more prone to becoming shy, stressed or aggressive. The cache does not report specific aggression data for Schizodon borellii itself, so a cautious keeper should provide generous space, cover and, where practical, a group, and avoid delicate long-finned tankmates as a precaution common to the family. This is a long-term, large-tank commitment, not an impulse purchase for algae control.
Conservation
Schizodon borellii is assessed by the IUCN Red List as Least Concern, consistent with a widespread distribution across the Paraguay River basin in Argentina and Brazil and no reported threatened populations. It is not known to be a significant target of the aquarium trade, and the cache does not report specific fisheries or habitat pressures acting on the species; its conservation picture is that of a common, unthreatened river fish within a large drainage rather than a range-restricted species of concern.