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Red-Bellied Pacu

Piaractus brachypomus

The 'Vegetarian Piranha' and the Tank Buster (60-80 cm / 2-3 feet). The Pacu represents the most irresponsibly sold fish in the entire aquarium industry. At 2 inches long, they look absolutely identical to the deadly, bloodthirsty Red-Bellied Piranha, complete with a gorgeous, glowing red belly. Unknowing beginners buy them thinking they are getting a badass killer. Instead, the Pacu is a peaceful, fruit-eating, skittish giant that explodes in growth to the size of a trash-can lid (weighing up to 50 lbs). They possess horrifyingly human-like square teeth for crushing walnuts, completely destroy all aquarium plants, and strictly require massive 1,000+ gallon indoor ponds.

Taxonomy

Class:Actinopteri

Order:Characiformes

Family:Serrasalmidae

Subfamily:Serrasalminae

Genus:Piaractus

Species:Piaractus brachypomus

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Water Temperature

24 - 28 °C

pH Value

6 - 7.5

Water type

Freshwater

Tank level

All levels

Adult size

88 cm

Minimum tank volume

>= 500 L

Minimum group

>= 1

2 - 15 dGH

1 - 7 dKH

TDS

40 - 295 ppm

Conductivity

63 - 461 uS/cm

Species description

Geographical Origin and Habitat: Broadly native to the massive, deep main channels and incredibly vast flooded jungle forests of the Amazon and Orinoco river basins in South America. During the long rainy season, the rivers flood the surrounding jungle for miles. The Pacu plays an absolutely vital ecological role: it swims directly beneath the massive canopy of flooded fruit trees, waiting for heavy, rock-hard tropical nuts and fleshy fruits to plummet into the water, eating them whole and dispersing the seeds miles away across the Amazon.

Taxonomy and Morphology: The Nut-Crushing Titan (Serrasalmidae). Closely related to the true Piranha, it shares the exact same iconic, deeply compressed (flattened side-to-side), tall, disc-like or diamond-shaped body. The jaw and head are incredibly thick and heavily muscled to support the bite force. The most famous, viral, and terrifying aspect of the Pacu is its teeth: while Piranhas have razor-sharp, interlocking triangular blades for shearing flesh, the Pacu's mouth is lined with two rows of massive, square, flat, horrifyingly HUMAN-LIKE molar teeth, perfectly designed for crushing the hardest nuts and seeds on earth into powder.

Social Behavior: The Nervous, Giant Sheep. They are completely peaceful, schooling, strictly herbivorous/frugivorous giants. They lack any of the aggressive, territorial, or bloodthirsty hunting instincts of true Piranhas. They are incredibly lazy, perpetually hungry, and graze the water column like aquatic cows. THE TRAGIC FLAW (The Panic Detonation): Despite their massive 50-pound bulk, they are inherently schooling prey-fish, making them notoriously nervous, skittish, and paranoid. A sudden shadow, turning on the room lights, or a loud noise will cause the massive fish to instantly panic and violently 'detonate', swimming at breakneck, blind speed directly into the glass or driftwood, causing horrifying injuries to themselves.

Coloration and Sexual Dimorphism: The Pet Store Deception. At 2 inches long, they are a breathtaking, stunning silver mirror with an absolutely radiant, fiery blood-red throat, belly, and anal fin, perfectly mimicking the lethal Red-Bellied Piranha as a defense mechanism against predators. AS GIGANTIC ADULTS: As they push past 15 inches, the beautiful red completely and depressingly fades away into a dull, dirty brown. They become massive, monotonous, dark charcoal-grey, dusty black, or drab silver, heavily-scaled slabs. Males and females look entirely identical to the naked eye.

Care, breeding and tankmates

Aquarium Setup: The 'Indoor Pond or Bust' Mandate (Tank Busters). Do not ever, under any circumstances, buy this fish for a standard home aquarium. A massive, tall, 30-inch long, heavy disc of pure muscle requires an absolute minimum of an 8 to 10-foot long (300+ cm / 800+ gallons) indoor heated tropical pond or massive custom acrylic tank. GLASS SHATTER WARNING: A panicked 40-pound Pacu will easily shatter standard 10mm glass with a single headbutt, flooding your house. You must use extremely thick glass or acrylic. DECORATIONS: Absolutely pointless. A Pacu will instantly eat, shred, and destroy any live plant, rip up fake plants, and knock over massive rocks, crushing glass heaters (use heavy PVC Sump filtration only). Keep the massive middle swimming area totally empty and void of obstacles.

Diet and Feeding: The Trash-Can Vegetarian (Frugivore/Omnivore). Feeding them is a joy because they are bottomless pits that will eat literally anything. In the wild, they crush rock-hard nuts. In the aquarium, they will ravenously devour whole blanched zucchinis, entire sliced cucumbers, boiled carrots, apples, grapes, lettuce heads, and spirulina discs. You can supplement their diet with massive jumbo Cichlid pellets and the occasional earthworm or peeled shrimp. DEADLY WARNING: Do not feed them heavy, constant meat diets (like goldfish or beef). They are vegetarians. Overfeeding meat causes fatal fatty liver disease, immense toxic waste, and severe bloat.

Water Quality: The Fecal Overload (Industrial Filtration Required). A 40-pound giant eating whole heads of lettuce produces unbelievable, staggering amounts of thick, rotting, organic fecal waste. If kept with a standard canister filter, the water will instantly turn cloudy, ammonia will spike to lethal levels, and the Pacu will develop severe 'Cloudy Eye' (bacterial burn) or 'Hole in the Head' disease (HITH) from toxic nitrates. You absolutely MUST use massive, industrial Pond Filters or giant Sumps, paired with brutal 50% weekly water changes. They require very warm tropical water (24-28°C / 75-82°F) and moderate, stable pH (6.0-7.5). High oxygenation via air stones or wavemakers is mandatory for their massive gills.

Compatibility and Cohabitation: The Giant, Peaceful Bowling Ball (Monster Comm Only). It is an incredibly peaceful, gentle giant that completely ignores other fish. BUT it is a massive, heavy, fast-moving object. It beautifully and harmoniously co-habitates with other massive Elite Monsters: adult Arowanas, giant Redtail Catfish, massive Datnoids, and giant Oscars. THE DANGER TO SMALL TANKMATES: While they are vegetarians and won't actively hunt small fish like Neons or Corydoras, if a small fish accidentally swims into the Pacu's mouth while it is blindly inhaling floating pellets, it will accidentally crush and swallow it without noticing. If they panic, they will violently smash into smaller, delicate tankmates like a bowling ball hitting pins, severely injuring them.

Aquarium Breeding: The Massive Farm Secret (Impossible in Captivity). Completely and utterly impossible to naturally breed in a 300-gallon glass box in your living room. Successful breeding only occurs in multi-acre outdoor mud ponds in massive Asian or South American commercial aquaculture fish farms (often grown for human consumption as a food fish). The farmers extract the massive adults, inject them directly with artificial pituitary hormones, and force them to spray millions of tiny eggs into the muddy water, which hatch into the millions of tiny 'Piranha-mimic' babies flooded into global pet stores.

Risks and Diseases: 1. THE STUNTING CRUSH DEATH (Spinal/Organ Deformation): The most infamous, horrific, and common tragedy in the hobby. The ignorant owner keeps the rapidly growing Pacu locked in a 55-gallon or 125-gallon tank. The massive, tall, disc-like fish hits the glass walls. Its massive spine permanently curls and folds into a 'U' shape to fit, horribly crushing and destroying its own internal organs (liver, stomach, heart), dooming it to a slow, agonizing, toxic, and depressed death by biological suffocation. 2. THE PANIC SKULL FRACTURE (Collision Death): The fish gets spooked by a loud noise, explodes into a blind, frantic sprint, and smashes its massive head into the glass or a large rock. The impact snaps its jaw, fractures its skull, and permanently disfigures the fish, often causing it to die of starvation or shock. 3. TOXIC AMMONIA BURN: Keeping the fish with inadequate filtration. The fish literally drowns and burns in its own massive output of urine and rotting feces, causing its eyes to permanently glaze over white with bacterial infection and rotting away its fins.

Geographic Origin and Distribution

Broadly native to the massive, deep main channels and incredibly vast flooded jungle forests of the Amazon and Orinoco river basins in South America. During the long rainy season, the rivers flood the surrounding jungle for miles. The Pacu plays an absolutely vital ecological role: it swims directly beneath the massive canopy of flooded fruit trees, waiting for heavy, rock-hard tropical nuts and fleshy fruits to plummet into the water, eating them whole and dispersing the seeds miles away across the Amazon.

Origin

Amazon, Orinoco, and GuianasNorth AmericaEurope, Mediterranean, and West Asia

Fish profile

Temperament: Semi-aggressive
Diet: Omnivore
Sex ratio: Solitary
Feeding frequency: Twice daily
Bioload: The Redbelly pacu produces a massive bioload due to its extremely large adult size and constant eating habits. Exceptional mechanical and biological filtration is absolutely essential. Keeping nitrates under control requires huge, routine water changes and meticulous tank maintenance.
Flow: Stagnant
Reproduction: Oviparous
Compatibility & tankmates: Despite their intimidating size and relation to piranhas, they are generally peaceful herbivores. They should be kept with other large, robust, and peaceful fish that will not nip their fins. Small fish may be accidentally eaten if they fit in the pacu's mouth, but they are not active predators.
Tank level: All levels

FishBase

Window to the official scientific data of the species

Data synced on: 06/15/2026

Scientific Parameters & Models

Trophic level: 2.5 ± 0.22 se
Resilience: Low (4.5 - 14 years)
Phylogenetic uniqueness (PD50): 0.625
Bayesian Length-Weight: a = 0.03162, b = 2.99

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

Related species

Recommendations grouped by close relatives, companion choices, and similar care.

Variants and close relatives

Same atlas type, nearby scientific identity, genus, or family.

Silver Dollar

Metynnis argenteus

Species description

Care, breeding and tankmates