Taxonomy & naming
Serrasalmus hollandi was described by Carl H. Eigenmann in 1915 and placed in the piranha genus Serrasalmus, within the family Serrasalmidae (piranhas, pacus and silver dollars) in the order Characiformes. The species epithet honours Dr. William Jacob Holland (1848–1932), the American entomologist, paleontologist and long-time director of the Carnegie Museum of Natural History, a common practice among early-twentieth-century ichthyologists naming species after museum patrons and fellow naturalists.
Serrasalmus is a taxonomically difficult genus — many species were described from a handful of preserved specimens over a century ago, and their limits have been repeatedly revised as more material and, more recently, molecular data have become available. Serrasalmus hollandi is explicitly flagged in the specialist piranha literature as one of the genus's less settled species, its status debated alongside close relatives such as S. humeralis, and a fuller taxonomic review has not resolved the question. This article follows the Catalog of Fishes' current treatment of the name and genus; it should be read as the best available placement rather than a final word.
Morphology
Like other members of Serrasalmus, S. hollandi has the classic piranha build: a deep, laterally compressed body, a blunt profile, an underslung lower jaw and a single row of interlocking, triangular, razor-edged teeth in each jaw. FishBase records a maximum published size of 7.5 in standard length, making it one of the smaller true piranhas rather than one of the large-bodied Serrasalmus species; aquarium-reported adult sizes run smaller still, commonly cited around 6 in.
Detailed published descriptions of colouration and fin proportions specific to S. hollandi are sparse in the available sources; as with many Serrasalmus, expect the typical silvery flanks with darker speckling and the humeral spot pattern used to distinguish species in the genus, though reliable field identification of Serrasalmus generally requires close comparison of dentition and body proportions rather than colour alone. No external sexual dimorphism is documented for this species in the sources reviewed.
Habitat
Serrasalmus hollandi is recorded from the Madeira River basin in Bolivia; its occurrence in Guyana is noted in the literature as uncertain rather than confirmed. FishBase classifies it as a freshwater, benthopelagic species in a tropical climate, consistent with the lowland river and floodplain habitats typical of Madeira-basin tributaries.
Detailed habitat descriptions — specific tributaries, seasonal water-level use, substrate or vegetation associations — are not available in the sources reviewed here; the data are sparse enough that this article does not speculate beyond the confirmed basin-level range.
Feeding
Aquarium literature describes Serrasalmus hollandi as a specialised fin-eater, biting pieces from other fish rather than attempting to consume them whole — a well-documented feeding strategy in several small-to-medium Serrasalmus species and one that fits the broader piranha pattern of opportunistic, often non-lethal predation rather than the pack-hunting myth. Within a mixed group of piranhas, conspecifics themselves are noted as being treated as a potential food source, consistent with the species' solitary, territorial temperament (see "In the aquarium").
In captivity it accepts frozen and live foods and will sometimes take pellets. As with other Serrasalmus, a varied diet of fish fillet, prawn and other meaty foods is preferable to a live-food-only regime, both for nutrition and to avoid the disease risk that comes with feeder fish.
Mating
No courtship behaviour has been documented for Serrasalmus hollandi in the sources reviewed. General accounts of Serrasalmus breeding biology describe conditioning on excellent water quality, an acidic pH and a temperature drop into the mid-20s °C as likely spawning cues, mirroring seasonal water changes in the wild, but none of this has been specifically confirmed for this species. Given its strongly solitary and aggressive temperament, any pairing attempt in captivity would need to be approached cautiously, with an escape route for a rejected partner.
Breeding
Breeding has not been documented in captivity for Serrasalmus hollandi, and the species does not appear in aquarium or commercial spawning records available to this article. As a true piranha, when breeding does occur in this genus it is expected to follow the same pattern seen in better-documented relatives: a pair clears and defends a substrate nest site among roots or plants, the female releases adhesive eggs that are guarded and fanned — most often by the male — and the eggs hatch within a few days. That pattern is inferred from the genus generally (and confirmed for genus-mates such as Pygocentrus nattereri) rather than confirmed for S. hollandi specifically, so it should be treated as a reasonable expectation rather than an established fact for this species. This account makes no claim of a mouthbrooding or bubble-nesting mode, and prospective breeders should expect data to be genuinely sparse.
In the aquarium
Serrasalmus hollandi is, like most of its genus, an "Einzelgänger" — a solitary fish that will not tolerate conspecifics and is particularly territorial and aggressive toward its own kind. It should be kept alone, not in a group; this is a firm departure from the shoaling Pygocentrus piranhas more commonly seen in the trade, and mixing multiple S. hollandi in one tank risks serious injury or death to the loser. Somewhat unusually for a Serrasalmus, hobbyist accounts note it can coexist with larger, faster fish that are neither small enough to be prey nor slow enough to be an easy fin-nipping target, though any tankmate should still be chosen with caution given the species' fin-eating habit.
Recommended water conditions from aquarium sources run cooler than many tropical characins, around 72–77 °F, with strong filtration to manage waste from a predatory diet. A well-planted tank with driftwood, rockwork and floating plants for shade suits its wary, cover-seeking nature. As with all Serrasalmus and Pygocentrus species, handle only by container rather than net, and check local and state law before acquiring one: piranhas are restricted or banned outright in many U.S. states and other jurisdictions, and this species should never be released into open water.
Conservation
The IUCN Red List assesses Serrasalmus hollandi as Least Concern, an assessment dated December 2020. Detailed population trend data and specific threats are not covered in the sources reviewed for this article; as with many single-basin Serrasalmus, the LC rating most likely reflects a lack of evidence for decline rather than a well-studied, monitored population, and it is not currently the subject of commercial fishery or dedicated conservation programmes noted in available sources. It is not a significant presence in the aquarium trade, which limits collection pressure but also means less incentive for captive-breeding programmes that might otherwise reduce reliance on wild-caught individuals.