Aquarist Atlas
Aquarist Atlas · piranhas, pacus & the big characins

Piranhas & Pacus

The big and oddball characins the Tetras section leaves out. Alongside the true piranhas (Serrasalmus, Pygocentrus) and their vegetarian cousins the pacus and silver dollars, this section covers the headstanders, the wolf fish and trahiras, the fanged payara and freshwater barracuda, the pike characins, and the African distichodus and citharinids. They are the characins with a reputation — and the section’s job is to separate the myth from the honest warning: most piranhas are wary fin-nippers, not man-eaters; the cute young pacu becomes a metre-long pond fish; the calm silver dollar will shred your plants; and the wolf fish will kill its tankmates. Built to the same standard as the cichlid, cory and pleco pages — researched, cited, no Wikipedia, no invented facts.

© Adobe Stock

This section covers the rest of the characins (order Characiformes) — every family the hobby meets except the small tetras, which have their own Tetras section (Characidae, the hatchetfish, pencilfish, Congo tetra and their kin). What’s left is the big, predatory and oddball side of the order: the piranhas, pacus and silver dollars (Serrasalmidae), the headstanders, the wolf fish, the payara and pike characins, and the African characins. Following the Catalog of Fishes for valid names — Serrasalmidae is being split hard, so the silver-dollar genera in particular are in flux — we group the families by a friendly ecology axis rather than by clade. Four honest themes run through every account. The piranha myth: most are shy scavengers and fin-nippers that need a group, not a frenzy. The size trap: pacus and the big predators are sold tiny and grow into pond fish — the adult size is stated plainly, and the pacu warning includes never release. Tankmate honesty: silver dollars shred plants, headstanders and some Africans nip fins and eat scales, wolf fish and payara eat their neighbours. And breeding is mostly egg-scattering, with the big food-fish farm-bred rather than home-bred. Read each account before you buy.

A red-bellied piranha in profile — silver flank, orange-red throat and belly, blunt jaw
A red-bellied piranha (Pygocentrus nattereri) — the face of the family and the source of the myth. In truth it is a nervous, shoaling fish that scavenges and nips fins far more than it hunts; it needs a group and heavy cover to settle, and a lone, exposed specimen is a stressed one. The jaws are real and command respect at feeding and netting, but the frenzy of film is the exception, not the rule.
A large, deep-bodied grey pacu with a blunt head and human-like molar teeth
A pacu (Colossoma, Piaractus) — the size trap at its worst. The “vegetarian piranha” is sold at 5 cm and grows to about a metre and 30 kg, crushing seeds and nuts with molar teeth unnervingly like a human’s. It is a pond and food-fish, never a living-room fish, and must never be released — feral pacus now turn up on several continents.

Photos © Adobe Stock

872 species in the atlas

Grouped by a friendly ecology axis — the piranhas, the pacus & silver dollars, the headstanders, the wolf fish & trahiras, the predatory characins (payara, freshwater barracuda and pike characins), the hemiodus & minor characins, the African characins and the South American darters — rather than by the shifting family boundaries, though each account names its current family and authority. This is the non-tetra half of one of the largest orders of fish; following the Catalog of Fishes and FishBase, the roster is deduplicated against the Tetras and Catfish sections, and new accounts are added as they are researched.

Species

872 of 872 species

Piranhas · 43

The true piranhas of family Serrasalmidae — the red-bellied shoaling Pygocentrus, the solitary Serrasalmus, and their kin (Pristobrycon, Pygopristis, and the scale-eating wimple Catoprion). The reputation is mostly MYTH: most piranhas are wary, opportunistic scavengers and fin-nippers, not the frenzy of film. The shoaling species (Pygocentrus nattereri) are nervous and need a GROUP and heavy cover to settle; the solitary Serrasalmus are territorial and kept one to a tank. Catoprion is a specialist scale-eater. The jaws demand respect at feeding and netting — but the honest risk is to tankmates and fingers, not a legend. Piranhas are restricted or banned in many regions; check local law before buying.

Pacus & silver dollars · 62

The plant- and fruit-eating side of Serrasalmidae. The pacus — Colossoma (tambaqui), Piaractus and Mylossoma — are the SIZE TRAP at its worst: sold at 5 cm, Colossoma reaches ~1 m and 30 kg, with human-like molar teeth for crushing seeds. They are pond and food-fish, never a living-room fish, and must NEVER be released — feral pacus turn up worldwide. The silver dollars — Metynnis, Myloplus, Myleus and kin — are peaceful, disc-shaped schoolers that need groups and open water, but they are committed PLANT-SHREDDERS that strip a planted tank bare. Mostly egg-scatterers; the big pacus are farm-bred.

Headstanders · 174

Families Anostomidae and Chilodontidae — the headstanders, named for the oblique, head-down posture they hold while grazing algae and picking at the substrate. The striped Anostomus and Leporinus are handsome but often nippy and territorial; many Leporinus grow large and turn aggressive with age, and several are notorious FIN-NIPPERS. The spotted headstander (Chilodus) is a gentler, smaller nano-grazer. Mostly herbivorous grazers that also relish soft plants; egg-scatterers rarely bred in aquaria. Keep the nippy ones in numbers or not at all.

Wolf fish & trahiras · 25

Family Erythrinidae — the wolf fish and trahiras (Hoplias, Hoplerythrinus, Erythrinus), plus the recently described swampfish Tarumania. Solitary, cylindrical, air-breathing AMBUSH PREDATORS armed with heavy conical teeth. Hoplias are large, powerful and genuinely aggressive — single-specimen fish that kill anything they can catch and can inflict a serious bite; the giant H. aimara exceeds a metre. The smaller Erythrinus and Hoplerythrinus ('red wolf fish') are more manageable but no less predatory. They gulp atmospheric air and endure deoxygenated pools. A specialist's predator, never a community fish.

Predatory characins · 41

The open-water hunters — the payara or vampire fish (Cynodontidae, Hydrolycus) with a pair of dagger-like lower fangs; the freshwater 'barracuda' (Acestrorhynchidae, Acestrorhynchus); and the pike characins (Ctenoluciidae, Boulengerella, Ctenolucius). Fast, streamlined, fragile-skinned pursuit predators of large rivers. Most are UNSUITABLE for home tanks: they need length to swim, panic and split their snouts against the glass, and eat fish tankmates. The payara reaches a metre and is a public-aquarium fish. Beautiful, demanding, rarely bred in captivity.

Hemiodus & minor characins · 288

A broad catch-all of mid-water and bottom characins the hobby meets less often. The hemiodus (Hemiodontidae) are fast, silver, shoaling dashers. The flannelmouth characins (Prochilodontidae — Prochilodus, Semaprochilodus) are large detritus-grazing migrators and major food fish. The toothless curimatas (Curimatidae) and scrapetooth Parodon (Parodontidae) are quiet substrate grazers. Bryconidae holds the powerful Brycon and the golden dorado (Salminus), a prized game fish; Triportheidae the keeled hatchet-tetras (Triportheus). Sizes and temperaments vary widely; most are egg-scattering shoalers and several grow large.

African characins · 122

The African branch — families Distichodontidae, Citharinidae and Hepsetidae. Distichodus runs from the peaceful nano Neolebias and Nannaethiops to the big, boisterous D. sexfasciatus and D. lusosso, which grow large and shred plants. The odd Phago and Ichthyborus are FIN-EATERS that rasp scales and fins from other fish. The deep-bodied citharinids (Citharinus) are grazers and important food fish. Hepsetus, the African pike-characin, is a lurking ambush predator with sharp teeth. A mixed group — read each account, because size and aggression swing hard between genera.

South American darters · 117

Family Crenuchidae — the South American darter tetras and sailfin characins. Small, often nano, bottom-perching fish that dart and rest like a true darter. The sailfin characins (Crenuchus spilurus, Poecilocharax) are prized blackwater nano-fish with fine finnage and a gentle, if shy, temperament — best in a species or quiet tank; Characidium are widespread stream-bed darters. Micro-predators on tiny invertebrates that often ignore flake — soft, acidic water and live or frozen foods suit them. Some are substrate egg-layers with brief male care.

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