South America's most notorious fish is plentiful in the Pantanal. Under the right conditions, they can live up to their voracious reputation - but entering the waters of the Pantanal doesn't necessarily mean you'll disappear in a tumult of thrashing waters.
Piranha have a robust, narrow body, and a blunt head. The jaw is thrust forward, containing triangular razor-sharp cutting teeth which interlock when closed. Adults typically measure 25-33 cm (10-13 in) - although other species such as the Black Piranha (Serrasalmus rhombeus) in the Amazon region can reach up to 45 cm (18 in). Relative to its size, the piranha has one of the most powerful bites of any animal - exerting up to 30 times its bodyweight. There are three species in the Pantanal.
National Geographic: Piranha
- Red-bellied piranha (Pygocentrus nattereri). This species is the most common species - and with the most fearsome reputation. Although named for their usually red belly, they can also appear orange or yellow. Some are so intensely gold-speckled that they are sometimes also called "Gold Dust piranha". They have a convex head-shape and sometimes red-coloured eyes.
- Ruby-red piranha or Gold piranha (Serrasalmus spilopleura aka. S. maculatus). Same size as the red-bellied. Can appear gold or yellowish, with black trim on their tail. Others of this species in the Amazon region have a bright orange-red underside. Slightly concave head-shape.
- Marginatus piranha or Pirambeba (Serrasalmus marginatus). Silver, with a yellow anal fin, tinged with black. Concave shaped head. This species has a preference for shady areas, hiding in vegetation close to the riverbanks. Adults measure up to 20 cm (8 in).
National Geographic: Piranha
Behaviour and Habitat
Everyone knows that piranha are carnivorous - but they're not entirely so. An analysis of the stomach contents for fish caught in the Pantanal shows a surprisingly high level of vegetable matter - particularly for P. nattereri and S. spilopleura, where appears to be a significant part of their diet. The non-vegetable portion of their diet consists of insects, crustaceans, fish eggs, scales/fins, and small vertebrates and fish. Piranha appear to be opportunistic scavengers more than mindless assassins - often exhibiting "grazing" behaviour where they quickly nip at other fish passing by (including other piranha). This is non-lethal to the prey. They also scavenge the carcasses of other dead animals in the water. Piranhas prefer to approach their prey from behind. Some fish, such as the oscar, have a false eye spot on their rear flank, causing the tail to resemble a head and deter piranha attacks.
Piranha hunt, but are opportunistic - targeting easy prey which appear old, weak, wounded or exhibiting signs of distress. Hence, the common triggers for attacks are splashing and the scent of blood. Strangely, the fact that piranha are prey for a multitude of other animals (e.g. dorado, jacaré, giant otters, amazon dolphins and numerous species of birds), makes piranhas timid - and is why they frequently stay together in shoals as a form of mutual protection.
Red-Bellied Piranha is really yellow.
The seasonal rise and fall of most waters where piranhas live is also directly and indirectly responsible for numerous piranha deaths. During the dry season many piranhas of all sizes become trapped in desiccating floodplain lakes and ponds cut off from the rivers. Most either die or become food items for predators and scavengers such as fish-eating mammals, wading birds, jacaré, water snakes and vultures.
Piranha attacks on people are rare - but their fearsome nature means they can quickly make headlines worldwide when they happen. Recent occurrences include attacks in Rosario (Argentina) and Cáceres (Mato Grosso, Brazil). The trigger large-scale attacks on beaches or riverside communities is unknown - but its suspected that the decrease in natural predators has led to an increase in piranha numbers. Lack of food, and warmer weather which increases the piranhas' metabolism have also been suggested as possible factors. As a result of attacks, wire mesh nets and public address systems have been installed around some popular river beaches. However, rather than mass attacks, random attacks where a single piranha takes a bite out of a passing swimmer or person wading through the water (i.e. piranhas exhibiting their natural "grazing" behaviour) does occasionally occur. Splashing tends to make piranhas more likely to attack, and children are often attacked for this reason.
The most dangerous period for attacks is usually the dry season. This is where the piranha are concentrated into smaller areas - and less food in the environment makes them more aggressive. This is less of an issue in major rivers where they are free to move further downstream - but lagoons and oxbow lakes can be especially dangerous.
Boi de Piranha
The expression "Boi de piranha" (piranha bull) is well-known in Brazil, with a meaning equivalent to the english "sacrificial lamb" or "scapegoat". This term originated in rural areas, such as the pantanal, where it referred to a practice adopted by cowboys crossing through piranha infested waters with their cattle herds. To reduce the risk of attack, they'd butcher an old or weak bull, then throw the carcass into the waters downstream. This would attract the shoals of piranhas - allowing the cowboys and their cattle herds to pass through upstream relatively unscathed.
Piranha reach sexual maturity around two years of age. They breed and spawn in the wet season, although the exact months may differ by region depending on conditions - being Nov-Dec in some areas and Apr-May in others. Observers have reported colour variations during the spawning period, with piranha exhibiting stronger colour on their belly, but appearing lighter overall. However, this isn’t consistent and there may be regional or species variations - as other observers have reported the opposite whereby the fish become darker.
During this spawning season, piranhas become more aggressive towards other fish as they pair up and defend their spawning territories. Spawning typically occurs in lagoons or in shallow water close to riverbanks, where the female lays clusters of 1,000 to 5,000 eggs in a bowl-shaped nest formed in sediment close to vegetation. These nests are 4-5 cm (1.5-2 in) deep, and around 15 cm (6 in) in diameter. Individual eggs measure about 3mm (1/8 in) in size. The nest is subsequently fertilised by the male.
Eggs hatch after two to five days depending on water temperature and species, with both parents staying nearby to protect their eggs and subsequent brood. Based on observations in aquariums, it appears that males choose the nest site, then create the bowl-shaped depression - sometimes removing excess vegetation by biting it with their sharp teeth. Notably, spawning doesn’t always go smoothly since males initiate courtship by actively pursuing a female - but it can sometimes end up in the mutilation or death of one or both fish.
Notes for Fishing
Piranha are among the most common fish in the Pantanal - meaning they’re also among the commonly caught. However, their sharp teeth pose a challenge, and there are two key things to remember:
- Be VERY careful removing them from your hook. Although your piranha bite scar might enthral listeners at a bar or pub in future as you recount and embellish your story - it really hurts, so probably isn’t worth it. Hold the fish firmly, behind the gills.
- Place a small length of leader wire above the hook. Don’t hang the hook directly on the fishing line as those sharp teeth will cut straight through the line (meaning you’ll lose both the hook and the fish).
Easy (but not recommended) piranha fishing method
Cooking Your Piranha
Piranha isn’t a great eating fish. It’s bony with very little meat. Its a sweetish meat and, while travelling with a Korean friend in the Pantanal we made some pretty good sushimi - although not a lot. However, they are plentiful, and the most common way to enjoy them in Brazil is with a broth known as Caldo de Piranha. This involves cooking the fish then dropping it into a blender. The flesh is liquified - with bones and being strained out through a mesh sieve and mixed with other ingredients.
Pantanal Recipes (including Caldo de Piranha)
Conservation and Threats
Since piranha are common throughout the Pantanal and Amazon regions they aren’t considered under any imminent threat. Despite their bad reputation, they’re important ecologically because they provide abundant prey for a wide variety of other animals such as jacaré, otters, Amazon river dolphins, and dorado. Their biggest threat comes from developments that degrade water quality such as large-scale agriculture and dredging.
- Piranhas are the most common fish in the Pantanal. They occur in virtually all places where there is water with some depth.
- Although piranha attacks in Pantanal rivers are extremely rare, caution is advised. Do not swim in areas where you see a lot of them. Don’t let them circulate around swimmers or divers.
- A large 12 kg pintado catfish can be devoured by a school of piranhas in less than two minutes. Once the prey is in the process of being stripped, other local fish such as piraputangas will also join in for a meal.
- If swimming in rivers with piranhas, the breaststroke is recommended since this causes less noise and stirring in the water. In closed ponds and lagoons it is recommended not to swim at all.
- Piranha have been reported in the waters of Florida and Thailand after supposedly having been dumped by aquarium owners or traders. However there hasn’t yet been any acknowledgment of them becoming a serious invasive species or threat in either location.
- In his book Exploration Fawcett, Colonel Fawcett describes execution by piranha which supposedly took place during the Paraguayan War. Those to be executed were tied to stakes in the water - then cut, leaving the piranha to do the rest.
Banner image: Piranha with mouth open (Shutterstock/Alberto Loyo).
Serrasalmus marginatus (Paul Louis Oudart); Red-bellied piranha (Shutterstock/Maxim Tupikov); Footer images: Piranha teeth (Shutterstock/Chris Howey); Red-Bellied Piranha (Shutterstock/kostudio); Cachara catfish in Pantanal market (Andrew Mercer)