Scientific Name:
PYGOCENTRUS PIRAYA.

Common Names:
Piraya, Piraya Piranha, Rio São Francisco Piranha, Black-tailed Piranha.

Range:
This species is only found in the Rio São Francisco, Brazil.

Maximum Size:
It is said that this species can reach up to 60cm. (24"), although there are no records of specimens of this size. In the home aquarium, this rare and expensive species has been grown up to at least 35cm. (14"), but it never reached its full potential size yet.

Body Characteristics:
P. Piraya looks very similar to the other members of its genus: bulldog-like face, high and steep forehead, and powerful lower jaw with very sharp teeth. The large eyes are silvery, with a dark diagonal 'band' for camouflage, and are positioned in front of the head. A feature unique among piranha's, is its tufted adipose fin. The coloration of the face, belly-region, anal and pectoral fins ranges from light yellow to deep red, with all possible colors in between. Another distinctive features that sets it apart from the other two members of the genus Pygocentrus is the fact that the belly coloration flames up, and may even extend to above lateral line.

Distinctive/unique features:

• Rayed adipose fin.
• Silvery eyes.
• Coloration on the flanks (also known as 'flames') extend above the lateral line.

  

  Tank:
  A well-planted tank will be appreciated, but according to owners of this species, it tends to be less shy than the far more common Red Belly Piranha. The Piraya can be very agressive towards it's own species, but on occasion also to other tankmates. It's attacks seem to be more efficient than other Pygocentrus-species, and when it strikes, the opponent is often left with a large open wound, as opposed to the head-butting, chasing and warning behaviour its relatives exhibit before starting an all-out attack. Perfect water quality is required to achieve maximum growth rate and good health (as with other species), but contrary to what some may think, this species is no more vulnerable to bad water conditions than it's relatives.
  
  Compatible Species:
  Pygocentrus nattereri, Pygocentrus cariba, Pygoncentrus ternetzi, Super Reds.

• Food:
  The same as the other members of the Pygocentrus family: live feeder fish, frozen fish and fish fillets, shrimps, krill and other crustaceans, insects, small mammals, fresh meat (chicken, beef) etc.

  
  

  Comments:
  The Piraya is the unchallenged king of all Pygocentrus piranha's (and from all carnivorous piranha's, only Serrasalmus Manueli can reach similar sizes), it is one of the biggest piranha's known. The Piraya is very similar in appearance to the Redbelly, with the exeption of a tufted adipose fin, unique to this species only, the more abundant, flame-like coloration on the sides, its massive, far more powerful lower jaw, and its silvery eyes (as opposed to P. Nattereri's red eyes). And it can grow almost twice as large as P. Nattereri.
  Because the Piraya only lives in one river (ie. Rio São Francisco), a river where fish catching for the pet industry occurs very infrequently, it is quite a rare site.

Optimal Water Conditions for Pygocentrus cariba Reproduction

Pygocentrus cariba, also known as the Orinoco piranha or black-spot piranha, is native to the lowland floodplains of the Orinoco River Basin in Venezuela and Colombia​ fishbase.se. To encourage breeding in captivity, one should closely mimic the natural water chemistry and seasonal physical conditions of its habitat​ monsterfishkeepers.com. 

In the wild, these piranhas experience distinct dry and wet seasons that dramatically alter water parameters (pH, hardness, temperature, dissolved oxygen, flow, etc.), and their reproductive cycle is tightly linked to these seasonal changes​ britannica.com, monsterfishkeepers.com. Below is a detailed overview of the Orinoco environment where P. cariba thrives, including how key parameters fluctuate through the year and trigger spawning.

Water Chemistry (pH and Hardness)

The waters of the Orinoco Basin where P. cariba lives are generally soft and slightly acidic. This river receives both sediment-rich “whitewater” (from Andean tributaries) and tannin-stained “blackwater” (from the Guayana Shield forests), resulting in a mix of water types​ aquaticecology.tamu.edu. As a result, pH can range roughly from ~4.5 up to ~7.0 depending on location and season​ monsterfishkeepers.com. 

Blackwater streams and floodplain lagoons (full of decaying plant matter) tend toward the lower end of this range (very acidic), whereas the main river channel and clearwater tributaries are often near-neutral. A typical pH around 6.0 is common in habitats of P. cariba​ monsterfishkeepers.com.

Likewise, the hardness and mineral content are low. Orinoco waters are often classified as soft water, with total hardness on the order of 2–8 °dH (German degrees of hardness)​ monsterfishkeepers.com. In parts of the upper Orinoco and blackwater areas, hardness can be at the low end (near 2 °dH, very soft), while whitewater influx can raise it slightly (approaching 6–8 °dH, still relatively soft). 

The softness reflects the low dissolved mineral content – blackwater from the ancient Guayana Shield carries very few dissolved ions, and although whitewater tributaries bring some minerals, the overall hardness remains modest​ aquaticecology.tamu.edu. In practical terms, water in P. cariba’s habitat often has <100 ppm of dissolved solids. The electrical conductivity is likewise low and varies with flow (higher in dry season, lower when diluted by rains)​ semanticscholar.org.

Tannins and clarity: Orinoco floodplain waters are often tea-colored from humic substances. During the rainy season, heavy runoff stains the water dark and can also carry suspended silt from the Andes, reducing clarity and light penetration​ aquaticecology.tamu.edu, aquaticecology.tamu.edu. 

In contrast, during the dry season, many pools and channels clear up (the sediments settle out and fewer new tannins enter), resulting in more transparent water. This seasonal difference in water color and chemistry is important for simulating a natural look in the aquarium (using peat or leaf litter to create a light tannin stain similar to blackwater). Maintaining slightly acidic, soft water year-round is crucial, but also consider a period of extra softness and acidity to mimic the flood season when breeding is to be triggered.

Temperature and Dissolved Oxygen

The Orinoco Basin lies in the tropics, so ambient temperatures are warm year-round. Water temperature in P. cariba’s natural habitat typically ranges from about 24–28 °C (75–82 °F) through the year​ monsterfishkeepers.com. There is little seasonal change in average temperature – the region’s climate is generally hot and stable (monthly means vary by only a few degrees)​ britannica.com. 

However, there are some patterns:

In the dry season (roughly Dec–March), air temperatures in the Llanos can get very high during the day (dry-season midday highs >35 °C are common)​
britannica.com. Shallow streams and lagoons under direct sun can warm above 30 °C in the afternoon, then cool a bit at night under clear skies. Thus, daily fluctuations are more pronounced in the dry months​britannica.com. Overall, dry-season water in shallow areas may be on the warmer side (upper end of 20s°C).
 

In the wet season (April–Sept), increased cloud cover and rainfall tend to moderate temperatures. Flooded waters are more extensive and often a bit deeper, which can buffer temperature swings. Typical wet-season water temperature stays in the mid-20s°C range (around 25–28 °C). The difference is not huge, but many observers note that the hottest water temperatures occur toward the end of the dry season when water is low and sun exposure is high​ britannica.com.
 

The table below summarizes how key parameters differ between the dry and wet seasons in the Orinoco (in the regions where P. cariba is common):

Sources: Seasonal patterns synthesized from environmental data​

britannica.com

​

britannica.com

; water chemistry ranges from field reports​

monsterfishkeepers.com

and floodplain studies​

semanticscholar.org

; dissolved oxygen dynamics from floodplain lake research​

horizon.documentation.ird.fr

.

Photoperiod and Light Cycle

As noted in the table, the photoperiod in the Orinoco Basin is roughly 12 hours year-round, due to its tropical latitude. Unlike temperate regions, there is no extreme difference between winter and summer day lengths – only about an hour difference between the shortest and longest days of the year. In P. cariba’s natural range (~5–8° N latitude), daylight will be ~11–12 hours in the dry season and ~12–13 hours in the wet season. 

Because this variation is mild, light cycle is a less dominant seasonal cue for breeding than the hydrology is. However, there is evidence that many tropical fish still use slight changes in day length or intensity to anticipate seasonal shifts. In the Orinoco, the wet season often brings more overcast days; conversely, the dry season skies are sunnier. So fish may associate increasing day length and softer, overcast light with the coming rains.

For captive simulation, providing a consistent 12-hour light:12-hour dark cycle is a good baseline. One can adjust it slightly (perhaps 11 hours in “dry season” phase and 13 hours in “wet season” phase) to mirror nature. Also, mimic the diffuse lighting of the rainy season – for example, using dimmer, filtered light during the “flood” period to simulate tannin-stained water under cloudy skies. 

The water itself in the tank should have a slight tea coloration (use driftwood, leaves, or peat filtration) especially during the breeding attempt, to replicate the natural light conditions P. cariba would spawn in.

Seasonal Cycle and Breeding Triggers in the Wild

Reproduction in P. cariba is strongly seasonal. In the wild, this species does not breed continuously year-round; instead it has a defined breeding season linked to the flood regime​ pubmed.ncbi.nlm.nih.gov. Field studies on Venezuelan populations have documented the annual cycle as follows:

Simulating These Conditions in Captivity

To replicate the optimal conditions for breeding P. cariba in an aquarium, an aquarist should aim to mimic the natural seasonal transition. Simply keeping the fish in static “good” water parameters may not induce spawning, because in nature the change of season is the trigger. Here are some guidelines drawn from both the wild data above and successful aquarium breeding practices:

By aligning tank conditions with the natural seasonal cues, breeders have successfully induced P. cariba to spawn in captivity. In summary, the optimal breeding conditions to replicate are those of the Orinoco early rainy season: warm (~27 °C), soft (near 0–4 dH), slightly acidic (pH ~6.0 or a bit below) water, with gentle flow and high oxygen, in an environment that has just transitioned from a period of hotter, stagnant conditions. This transition – from “dry” to “wet” – is the key to unlocking their reproductive cycle, just as the flood pulse triggers it in the wild​ pubmed.ncbi.nlm.nih.gov, monsterfishkeepers.com. By paying close attention to pH, hardness, temperature, flow, photoperiod, and other factors as outlined above, one can closely simulate the Orinoco River Basin conditions and greatly improve the chances of successful captive breeding of Pygocentrus cariba.

Sources:

This cycle is clearly tied to the environment: P. cariba “chooses” the flood season to reproduce because it maximizes survival chances for the next generation. The flood brings (1) spatial expansion – many safe, vegetated areas to lay eggs, which reduces predation on eggs/larvae; (2) food surges – floodwaters trigger blooms of productivity (invertebrates, fruits, detritus) that feed the fry and their prey; and (3) relatively stable, warm water conditions for egg incubation (no sudden chilling). A study of Orinoco fishes confirms that the annual gonadal cycle of P. cariba is “closely related to changes in the annual hydrologic cycle of the Orinoco,” i.e. the inundation (flood) and isolation (dry) phases​ pubmed.ncbi.nlm.nih.gov.

For captive breeding, experts recommend maintaining temperatures at the upper end of the natural range when attempting to spawn P. cariba. In practice, this means around 29 °C (~84 °F) during the induced “spawning period”​ monsterfishkeepers.com. This is slightly above their usual average, mimicking the warm shallow conditions that might occur in nature at the onset of the rains.

Dissolved Oxygen (DO): P. cariba lives in well-oxygenated waters but can also tolerate the somewhat lower oxygen levels found in stagnant floodplain pools. In the dry season, many of the waters are shallow and often fully mixed by wind and daytime heating, so DO levels tend to stay high (often near air-saturation, ~6–8 mg/L in daytime)​ horizon.documentation.ird.fr. 

Because dry-season pools are small, wind stress can stir the entire water column, preventing stratification of oxygen. Indeed, studies of Orinoco floodplain lakes found they were almost entirely unstratified at low water – temperature and oxygen were uniform top to bottom due to constant mixing​ horizon.documentation.ird.fr. Thus, fish trapped in isolated lagoons during the dry season generally have adequate oxygen (except in extreme drought cases where pools might stagnate or start to dry out).

During the wet season, the picture changes slightly. As rains flood the plains, a huge amount of organic matter (soil, leaf litter, etc.) is suddenly submerged. Bacterial decomposition of this material consumes oxygen, and the flooded areas are larger and often sheltered by vegetation (less wind mixing)​ horizon.documentation.ird.fr , horizon.documentation.ird.fr. As a result, DO can dip in the flood season, especially in the depths of floodplain lakes or during the night. Researchers have observed that at high water some Orinoco flood lakes developed hypoxic conditions near the bottom (low DO) until the water began receding​ horizon.documentation.ird.fr , horizon.documentation.ird.fr. However, complete anoxia is rare because the Orinoco’s floodplain lakes are relatively shallow (typically <6 m deep) and get periodically mixed by river inflows​ horizon.documentation.ird.fr, horizon.documentation.ird.fr. 

In fact, the main river channels remain fast-flowing even at flood, so they carry plenty of oxygen. P. cariba often spawns in shallow vegetated areas of the floodplain (where plants can produce oxygen in daytime), so daytime DO during spawning is likely sufficient. Still, it’s natural for them to experience slightly lower nighttime O₂ levels in flood season.

Captive tip: Ensuring good oxygenation in the aquarium is important (use air stones or surface agitation), but some breeders even mimic the stagnant conditions briefly – for example, during a simulated “dry season” they might lower water flow (turn off filters for a short period)​ monsterfishkeepers.com. This approach reflects the calmer, lower-oxygen waters of dry-season pools, but one must be cautious to not suffocate the fish. Generally, keeping dissolved oxygen around saturation (≥5 mg/L) is recommended, with perhaps a slight dip during the “dry” phase if simulating one, and then strong aeration when “rains” return.

Flow Regime and Seasonal Water Levels

One of the most critical environmental cues for Orinoco fishes is the annual flood pulse. The region has a stark dry season (low water) and wet season (flood), which dramatically alter water depth and flow​ britannica.com , britannica.com. P. cariba evolved in this floodplain ecosystem and times its reproduction around the flood cycle. Key aspects of the hydrology include:

• During the late dry season (roughly January through April), P. cariba adults undergo gonadal maturation – their ovaries and testes develop in preparation for spawning​ monsterfishkeepers.com. By the end of the dry season (around April or early May), most adults are in prime breeding condition (high gonadosomatic index, ripe eggs/sperm present)​ monsterfishkeepers.com. Ecologically, this corresponds to a period when waters are still low (“isolation” phase) but the fish sense the coming change in environment.
   

• As the rains arrive and waters rise (May–June), the conditions become favorable for spawning. The actual spawning of eggs and fertilization typically occurs in the mid-wet season, primarily July and August in the Orinoco floodplains​
  monsterfishkeepers.com. By this time, the floodplain is fully inundated, providing abundant space and food (in the form of insects, crustaceans, and smaller fish flushed out by the flood) for the offspring. Spawning in July–August means the peak of hatchling and fry presence is during August–September, when the flood waters are still widespread. Notably, researchers report P. cariba’s reproductive peak in May–June, with actual spawning stretching into July–August as water levels climax​ monsterfishkeepers.com. This suggests that early in the wet season (late May or June), the fish may start spawning in response to rising water (some initial spawns), and spawning activity continues through the height of the flood. By the end of the wet season (late August or September), spawning activity tapers off as adults likely shift focus to feeding and the young-of-year grow before waters recede.
   

• Once the waters recede (late wet season into early dry season), spawning stops. The floodplain drains and young piranhas either move to permanent water bodies or perish if trapped in drying pools. Adults then have a rest period during the early dry season when they recover and feed, and their gonads remain spent until the cycle repeats with new maturation after a few months of rest​ monsterfishkeepers.com.
   

• Baseline Water: Maintain soft, slightly acidic water as the default. Aim for ~5.5–6.5 pH and very low hardness (use peat or RO water to achieve ~2–6 °dH)​ monsterfishkeepers.com. Temperature can be kept around 26–27 °C during the non-breeding period (comfortably within their natural range).
   

• Dry Season Simulation (conditioning phase): Increase temperature a bit (toward 28 °C) and let water level in the tank drop or remain lower. Some breeders actually lower the water level by ~20% for a few weeks to simulate the shallow waters of the dry season​ monsterfishkeepers.com. During this time, feeding should be heavy and nutritious – this corresponds to the conditioning period when fish build up reserves and gonads develop (analogous to Jan–Apr in nature). Keep the water somewhat stagnant but aerated: for example, reduce filtration flow (even turn off filters for a week, relying on an airstone for minimal circulation)​monsterfishkeepers.com
  . This mimics the still, warm, oxygen-poorer environment of dry-season pools and can help trigger physiological changes. Ensure the fish are not stressed – the idea is warm, “stagnant” water rich in food, which tells the fish it’s drought time but they are well-fed (a precursor to upcoming rains).
   

• Rainy Season Simulation (spawning trigger): After a set period of “dry” conditions (hobbyists often use ~1–2 months of conditioning), introduce the “flood.” This involves adding cooler, soft water to fill the tank back up, dropping the temperature slightly (perhaps from 28 °C down to 26–27 °C)​ monsterfishkeepers.com. The fresh water should be very soft and slightly acidic (like heavy rain), achieved by using deionized or rainwater-conditioned water. At the same time, restart strong filtration and aeration – the return of currents simulates river inflow​ monsterfishkeepers.com. Many breeders also add peat extract or tannins at this stage to tint the water (signaling “wet season” chemistry)​ monsterfishkeepers.com. The “rainy season” changes should be done in concert: rising water level, slight temperature drop, softness increase, and perhaps a drop in barometric pressure if possible (some aquarists time water changes with actual storms in their area, noting that piranhas may respond to barometric pressure changes)​ monsterfishkeepers.com. According to reports, P. cariba often begin courtship and nest-building behaviors soon after these changes if they were properly conditioned prior.
   

• Spawning Behavior: In the wild, P. cariba spawn in flooded grassy or root-filled areas. In the aquarium, provide a similar setup – e.g. one side of the tank densely planted or with tangles of roots and some fine sand or leaf litter substrate​ monsterfishkeepers.com. Males will excavate a shallow “nest” in the substrate or use the base of plants to deposit eggs​ monsterfishkeepers.com. Dominant males may darken in color, and females often become aggressive as spawning approaches​ monsterfishkeepers.com. Ensuring some private, secluded sections of the tank (use partitions or visual barriers) is important because piranhas can be shy about human presence during breeding​ monsterfishkeepers.com.
   

• Guerrero et al. (2009) study on Venezuelan floodplain fishes – showed P. cariba’s annual cycle tied to flood season​ pubmed.ncbi.nlm.nih.gov, monsterfishkeepers.com.
   

• OPEFE (Orinoco water chemistry data) – provided pH, hardness, temp ranges​
  monsterfishkeepers.com  and breeding guidelines from experienced aquarists​
  monsterfishkeepers.com.
   

• Britannica & hydrology studies – described Orinoco seasonal depth, flow, and climate patterns​ britannica.com, britannica.com, comptes-rendus.academie-sciences.fr.
   

• Vasquez (1992) floodplain lake research – details on temperature and oxygen stratification in Orinoco vs Amazon flood conditions​ horizon.documentation.ird.fr, ​
  horizon.documentation.ird.fr.
   

• Aquarium sources (MonsterFishKeepers forum, Aqua-fish guide) – practical parameters and successful spawning anecdotes​ monsterfishkeepers.com, monsterfishkeepers.com.

• Dry Season (Approx. Oct–March): Rainfall is minimal, and the Orinoco River recedes to its low-water mark. By the end of the dry season (Feb–March), the river is at its shallowest. For example, near Ciudad Bolívar (in the lower Orinoco), the river depth averages about 15 m (~49 ft) during low water​ britannica.com. Many off-channel habitats shrink or dry up: vast tracts of the Llanos grasslands turn into patchy wetlands or isolated oxbow lakes. Water flow in the main channels slows significantly, and tributaries coming from rain-fed plains may dwindle to a trickle. In the floodplain, what were large lakes become small pools or disconnected “ponds” in this period (local people refer to this as the time of “aguas bajas” – low waters). Currents in smaller streams are also much weaker in the dry season. Overall, fish like P. cariba experience more confined, still water conditions and higher density of fish in remaining water bodies during these months.
   

• Wet Season (Approx. April–Sept): As the Intertropical Convergence Zone shifts northward and rains return around April​ britannica.com, the Orinoco and its tributaries begin to swell. The river’s rise begins in April at the start of the rains​
  britannica.com, and by June–July the water level is climbing rapidly. The Orinoco reaches its “high-water” peak around July, which in the lower basin means an astonishing depth of ~50 m (~165 ft) at Ciudad Bolívar​, britannica.com. From June through August, the Llanos floodplains are extensively inundated – what were grasslands become a vast shallow lake or marshy expanse​ britannica.com , ​
  britannica.com. In some places the flood can submerge the land by up to 20 m (65 ft) of water​ britannica.com, though typical flood depths over the plains are on the order of 1–5 m. The breadth of the Orinoco River expands dramatically as well (in places it can swell to over 20 km wide during floods​ gettyimages.com).
   

• Flow and Current: During the peak wet season, the river’s discharge is massive. The Orinoco ranks among the top three rivers globally by volume; at peak flow it pushes ~37,600 m³/s of water towards the ocean​ comptes-rendus.academie-sciences.fr. Main river channels have strong currents in this period, and turbidity is high from sediment load. However, P. cariba often retreats into the calmer floodplain lagoons and submerged forests to spawn. In those flooded areas, water flow is much gentler – essentially still water among the grass and bushes, with only slow exchange as the floodplain drains back gradually. So in the wet season the piranha have the best of both worlds: plenty of fresh water and space, but not necessarily fighting strong currents except when they move back to the main river after floods. By October, the rains taper off and water levels fall, entering the next dry phase.
   

•