Edit Serrasalmus rhombeus

You can suggest changes to this profile. A moderator will review each change.

Name

Scientific name

Serrasalmus rhombeus

Described by

Not recorded

Family

Serrasalmidae

Common names

Black Piranha/Rhom

Photograph credits

All 2 credited

Summary

Serrasalmus rhombeus, known as the black piranha or rhom, is a large piranha recorded from much of northern South America. It occurs in num…

Size and aquarium

Maximum size

450mm, standard length

Aquarium size

Minimum length 210 cm, Minimum depth 45 cm, Minimum height 45 cm

Water

Water conditions

22.2–27.8°C

Hardness

1–20dGH

Conductivity

Not recorded

Behaviour

Temperament

Species tank only

Community suitability

Not recorded

Where it lives

Countries, regions, rivers and lakes

Amazon, Negro, Orinoco

Writing

Etymology

Not written yet

Distribution

This species is widespread in nature although the true extent of its range is an issue for debate. Officially it's been recorded from Venezuela, Guyana, Surina…

Habitat

Inhabits a range of biotopes but as an adult is particularly associated with larger, deeper river channels where it's typically found hunting in deep water or …

Aquarium size

This is an active, riverine species. A single, fully-grown adult would need a tank measuring upwards of 210 ∗ 45 ∗ 45 cm to itself.

Maintenance

Requires a well-oxygenated set-up, ideally furnished with a sandy substrate and some driftwood roots and branches to provide cover. You can attempt to grow aqu…

Water conditions

Temperature: 22.2 – 27.8 °C pH: 4.5 - 7.5 Hardness: 1 - 20°H

Diet

Wild fish are opportunistic, feeding on the fins and flesh of other species as well as smaller fishes, insects and crustaceans. They have also been recorded sc…

Behaviour and compatibility

Should only be considered as a specimen fish for the enthusiast since it doesn't make a good tankmate for anything else. Scattered reports of it coexisting wit…

Sexual dimorphism

No external sexual differences between the sexes have been recorded although females in spawning condition are usually plumper than males.

Reproduction

This species has only rarely been bred in captivity with the main restriction appearing to be the volume of water required to avoid the fish murdering one anot…

Notes

There are in excess of 30 described species of Serrasalmus many of which appear superficially similar and have confusing taxonomic histories. S. rhombeus is am…

There are in excess of 30 described species of Serrasalmus many of which appear superficially similar and have confusing taxonomic histories. S. rhombeus is among the most convoluted of all with numerous synonyms of which S. niger is the most well-known. There has also been a muddle surrounding the common names "white" and "black" piranha, both of which have been used to describe the species.

Of greater interest to both scientists and hobbyists has been the discovery of numerous geographical forms, some of which vary considerably in size, body form and colouration. The primary feature linking these is the deep red eye that characterises mature specimens and the existence of a species complex has been suggested by several authors. In addition some species in the genus (e.g., S. aureus, S. hollandi) were described using what is now considered to be insufficient data and may turn out to be synonymous with S. rhombeus.

Juveniles are particularly tricky to identify correctly as they lack the red eye until they are around 5"/12.5 cm5 in in length, and share their spotted patterning with some other species. We've seen young S. rhombeus mislabelled as S. marginatus, S. sanchezi and S. compressus among others. To illustrate the difficulties involved, the specimen in the second image above was sold as and confirmed by several experienced piranha keepers as S. marginatus but turned out to be an S. rhombeus variant after more than a year in captivity.

Some of the forms are highly-prized in the hobby and have been assigned specific vernacular names. Ostensibly implemented to ease identification, these have instead added to the confusion, with exporters/dealers frequently attaching false locality details to fish in order to increase their value. The more commonly seen ones include the rio Xingú form, the so-called "Diamond" forms and the "Jet Black/High-back" Peruvian fish with its characteristically deep body. Fish from Venezuela are often referred to using the nickname "Vinny" by enthusiasts.

Most experts agree that a detailed revision of Serrasalmus is necessary since historically the genus has been viewed as something of a "catch-all" for similar-looking fin-biting/predatory characins for decades and has long-been regognised a polyphyletic grouping. There have been several attempts to reorganise the group with the most recent major revision published by Géry in the late 1970s but a handful of new species have been described since then and an exhaustive molecular analysis of member species remains lacking.

The family Serrasalmidae consists of over 60 species in 16 genera and also includes the seed and fruit eating tambaquis and pacus among others. Their characteristic features include a compressed body shape, long dorsal fin with 16 or more rays and possession of sharp serrae on the ventral surface formed by modified abdominal scales. The number of the latter is variable, ranging from 6-9 in Acnodon to over 60 in Piaractus spp..

Members display three main feeding habits: carnivory (flesh-eating), frugivory (fruit and seed-eating) and lepidophagy (eating the scales and fins of other fishes). Carnvirous species normally possess a single row of tricuspid teeth on each jaw, frugivores tend to have two series of incisor or molariform teeth on the premaxilla, one row of teeth on the dentaries, and often a pair of symphyseal teeth, while in lepidophages the teeth are tuberculated and located on the outer side of the premaxilla.

Based on the results of their mitochondrial DNA-based phylogenetic analyses of serrasalmids Ortí et al. (2008) recommended that member genus Pristobrycon be restricted to contain just the single species P. striolatus with all other members placed in Serrasalmus, to which they are more closely-related, but this concept appears not to have achieved general acceptance at time of writing.

In South America only Pygocentrus species are referred to as "piraña", with Serrasalmus and other related genera being referred to by other names such as "Pirambeba". Serrasalmus species are therefore not considered to be "true" piranhas, the name being applied to them by the English-speaking world and aquatic hobby.

It should also be said that serrasalmids are not the fearsome "monster fish" as often depicted by the media. Obvious care must be taken when performing tank maintenace but these fish will usually only bite when threatened, and they can be quite skittish in an aquarium setting unless their rather specialist needs are catered for. Most also live in excess of ten years and become less active as they mature so careful thought is required before purchasing one as they represent a considerable investment.

Editing needs JavaScript. This is the text as it was last saved.

Where does this come from?

My own experienceFor example, I've kept twelve in a planted 60 cm tank since March 2024.A website I sawFor example, an IUCN Red List assessment, a museum catalogue or a FishBase page.A paperFor example, Marshall et al. (2011), Water temperature differences in interfluvial palm swamp habitats of Paracheirodon axelrodi and P. simulans.A book, or something not onlineFor example, Tappin (2010), Rainbowfishes: their care and keeping in captivity.Something already on the pageFor example, the Behaviour and compatibility section already says this.

Web address

Paste the address of the page that says this. What counts as a source

DOI

Paste a DOI and we will look up the rest of the reference. A DOI looks like 10.11646/zootaxa.4694.4.1, and most papers print it on the first page.

Title

Enter the title of the paper, book or page. If you leave it empty, we will use the website's address.

Authors

Separate authors with semicolons, e.g. Tan, H.H.; Ng, P.K.L.

Year

Journal or publisher

Pages

Enter the page that says this, e.g. 218 or 218–221.

Anything worth adding

Describe what you saw, or which part of the source says this.

References

No references

Name

Scientific name

Described by

Family

Common names

Photograph credits

Summary

Size and aquarium

Maximum size

Aquarium size

Water

Water conditions

Hardness

Conductivity

Behaviour

Temperament

Social needs

Community suitability

Where it lives

Countries, regions, rivers and lakes

Writing

Etymology

Distribution

Habitat

Aquarium size

Maintenance

Water conditions

Diet

Behaviour and compatibility

Sexual dimorphism

Reproduction

Notes

References

References