Piranha Fish: Types, Feeding, Reproduction, and Rearing

Piranhas are iconic animals of the Amazon (Machado et al., 2018), but they have gained a notorious reputation due to movies portraying them as ruthless killers of humans. However, these extraordinary fish have long captivated the imagination of adventurers and scientists.

Despite their fearsome reputation, piranhas are not mindless killers as often depicted in movies and popular culture. In this article, we provide you with a general overview of the different types of piranha fish, their feeding, reproduction, and rearing.

Taxonomy and Characteristics of Piranhas

Piranhas are a group of fish belonging to the family Serrasalmidae and the genera Serrasalmus, Pygocentrus, Pygopristis, and Pristobrycon (Machado et al., 2018). They are characterized by having a row of tricuspid teeth in their upper and lower jaws (Thompson et al., 2014).

The taxonomic classification of piranhas is as follows:

Phylum: Chordata

Class: Actinopterygii

Order: Characiformes

Superfamily: Erythrinoidea

Family: Serrasalmidae

Genera: Serrasalmus, Pygocentrus, Pygopristis, and Pristobrycon

Common Names: Piranha, Caribe, Red-Bellied Piranha, Red-Bellied Piranha

These freshwater fish are known for their distinctive appearance, characterized by sharp teeth and robust bodies.

Piranhas have a streamlined body shape that allows them to move quickly through the water. Depending on the species, piranhas can reach a length of 12 to 35 cm, an average weight of 300 grams, and can live up to 10 years.

Their powerful jaws are equipped with interlocking sharp teeth, perfectly designed for tearing flesh. Contrary to popular belief, piranhas do not have a bite force strong enough to sever limbs or prey on larger animals. Instead, they rely on their large numbers and coordinated attacks to overwhelm their prey.

The coloration of piranhas varies depending on the species and their habitat. Most piranhas have a silver or grayish body with dark spots or stripes, providing effective camouflage in turbid waters. This allows them to ambush unsuspecting prey and avoid detection by predators.

Some species, such as the red-bellied piranha, display vibrant colors during mating rituals, exhibiting their vibrant red or orange bellies as a sign of dominance.

Habitat

Piranhas are mainly found in freshwater rivers, lakes, and flooded forests of South America, particularly in the basins of the Amazon, Orinoco, and Paraná rivers. These regions provide abundant food sources and suitable breeding grounds for piranhas. They are particularly abundant in areas with dense vegetation, as this provides ample hiding places for them to ambush their prey.

These fish are highly adaptable and can thrive in diverse aquatic environments, from fast-flowing rivers to aquaculture ponds. Their ability to survive in such varied habitats is a testament to their remarkable adaptability.

Despite their preference for freshwater habitats, Caribe are also known to venture into brackish and even saltwater environments. This adaptability allows them to colonize new territories and expand their range. In recent years, there have been reports of Caribe found in unexpected places, such as rivers in Florida, United States. These occurrences highlight the piranhas’ ability to survive and thrive in different ecosystems.

Rahman et al. (2008) reported that piranhas have been introduced in Thailand, China, Singapore, the Philippines, and Bangladesh.

Types of Piranhas

There are more than 30 recognized species of piranhas, each with its own characteristics and unique adaptations.

Red-Bellied Piranha (Pygocentrus nattereri)

The red-bellied piranha or red piranha (Pygocentrus nattereri) is the most well-known and commercially available in aquariums. This fish is commonly found in rivers and lakes of South America, primarily in the rivers of northeastern Brazil and the basins of the Paraguay and Paraná rivers. The red-bellied piranha can grow up to an average length of 29 cm (Bevilaqua et al., 2010).

This species is known for its aggressive behavior and sharp teeth, making it a formidable predator. Although this piranha species is primarily a carnivorous piscivore, it can be opportunistic and feed on plants, insects, worms, and crustaceans (Schartl et al., 2019).

Pygocentrus nattereri exhibits social behavior and swims in shoals, typically consisting of 20 to 30 fish that feed together. These fish can withstand long periods of prey scarcity and hunger.

The red-bellied piranha is often confused with the pacu (Piaractus brachypomus) due to their similar belly coloration.

Black Piranha (Serrasalmus rhombeus)

Another notable species is the black piranha or caribe (Serrasalmus rhombeus), which is the largest and most powerful piranha species. With its robust body and strong jaws, it is capable of crushing snail shells and crustaceans. The black piranha is also known for its territorial nature, fiercely defending its territory against intruders.

Other Piranha Species

Other species, such as the white piranha (Serrasalmus brandtii) and the yellow piranha (Serrasalmus maculatus), have their own unique characteristics and adaptations. Despite their differences, all Caribe species share common traits such as sharp teeth, predatory behavior, and the ability to survive in diverse aquatic habitats.

Feeding Habits and Diet

Piranhas are known for their voracious appetite and frenzied feeding behavior. Contrary to popular belief, they do not solely rely on consuming meat and are not indiscriminate killers. While piranhas have a carnivorous diet, their feeding habits are more complex and varied than commonly described.

Schartl et al. (2019) highlight that piranhas are known for a unique combination of morphological, physiological, and behavioral traits, making them the top freshwater predators in their habitats.

Theses fishes are opportunistic feeders, meaning they will consume any available food source. Their diet consists mainly of fish, crustaceans, insects, and even plant matter.

It is important to note that piranhas do not typically prey on larger animals such as humans. They are more likely to scavenge on carcasses or attack smaller, wounded prey. Cases of Caribe attacking humans are extremely rare and usually occur when the fish feel threatened or cornered.

In captivity, Khan et al. (2010) report that piranhas (Serrasalmus spilopleura) can be trained to eat almost any meaty food, including goldfish, rosies, small tetras, frozen fish (cod, catfish, salmon, tuna, etc.), shrimps, krill, mussels, squid, insects, and even small mammals (mice, etc.), reptiles, and amphibians.

Regarding this, Mirzabagheri et al. (2016) studied 17 different diets in the feeding of P. nattereri and concluded that a diet with live worms allows for the highest growth rate.

Behavior of Piranhas and Social Structure

These fishes are highly social animals that exhibit complex behaviors and social structures. They are known to form tightly knit groups, called shoals or schools, which can consist of hundreds or even thousands of individuals. These groups provide protection for piranhas, increased hunting efficiency, and opportunities for reproduction.

Within a shoal, piranhas establish a hierarchy based on size and dominance. Larger and more dominant individuals occupy the primary feeding and breeding territories, while smaller individuals hold subordinate positions (Oldfield et al., 2023). This social structure helps maintain order within the group and ensures that food resources are distributed fairly.

Communication among Caribe is mainly through visual signals and body language. They use fast movements, fin displays, and changes in coloration to communicate with each other. These signals can convey aggression, submission, courtship, and other social interactions. By observing these behaviors and signals, scientists have gained valuable insights into the complex social dynamics of piranhas.

Reproduction and Life Cycle

Piranhas have a unique reproductive process that is closely linked to the annual flood cycles of their habitats. Queiroz et al. (2010) report that piranhas have two annual reproductive seasons in their natural environment, synchronized with water level fluctuations and flood pulses.

Sexual maturation in male and female Caribe occurs when they reach a length of around 16 cm. Sexually active male and female red-bellied piranhas darken in color and lose most of their red pigmentation.

However, for piranhas of the species Serrasalmus rhombeus, S. gouldingi, and Pygocentrus cariba, their colors intensify to the point that their overall tone is almost black (Germain, 2017).

Female red-bellied piranhas, Pygocentrus nattereri, have up to 30,000 oocytes, but only about a third of them are mature and available for spawning in a single batch (Queiroz et al., 2010).

Females deposit their eggs in shallow waters or among vegetation, where males fertilize them. The eggs are adhesive and attach to plants or submerged objects for protection. The parents guard the eggs until they hatch, ensuring their safety from predators.

Once born, piranha fry are relatively independent and grow rapidly. They feed on small invertebrates, algae, and other microorganisms until they reach maturity. The exact time it takes for piranhas to reach maturity varies depending on the species and environmental conditions. During this time, they will form shoals and establish their social structures, preparing to continue the cycle of life.

Breeding Piranhas

In some aquarium stores, you can find Caribe specimens; however, it’s important to note that in some countries, such as the United States and the Philippines, the commercialization of these fish for breeding in aquariums is prohibited.

The most common type of piranha available in the ornamental trade is Pygocentrus nattereri, the red-bellied piranha. Piranhas can be purchased as adults or young ones, often no larger than a thumbnail.

It is important to keep Pygocentrus piranhas either alone or in groups of four or more, not in pairs, as aggression between them is common, weaker fish won’t survive, and aggression is more widely distributed when kept in larger groups.

In the table 1 below, we present the main optimal ranges of water quality parameters for the ornamental breeding of red-bellied piranhas (Pygocentrus nattereri) in aquariums. It is important to note that piranhas are NOT a good choice for a community aquarium as they will eventually consume other fish or shrimp.

Table 01. Water Quality Parameters for Ornamental Breeding of Piranhas.

Myths and Misconceptions about Piranhas

Piranhas have long been the subject of myths and misconceptions fueled by sensationalized portrayals in the media and popular culture. While these misconceptions have added to the fearsome reputation of piranhas, they often obscure the true nature of these extraordinary creatures.

A common misconception is that piranhas hunt in large packs, devouring everything in their path. In reality, piranhas are more likely to feed in small groups or individually. They rely on their sharp teeth and swift movements to catch and immobilize their prey, rather than overwhelming them through sheer force in large groups.

Another myth is that piranhas are attracted to blood and will attack anything that is bleeding. While piranhas can detect blood in the water, they are not solely attracted to it. They are more likely to be drawn by the sight and sound of struggling prey, rather than the presence of blood alone.

It is also important to dispel the myth that piranhas are man-eaters. These fish do not typically prey on larger animals, and cases of piranhas attacking humans are rare. When such encounters do occur, they are usually the result of mistaken identity or defensive behavior. It is crucial to understand the true nature of piranhas and not fall victim to exaggerated stories and misinformation.

Mol (2006) reported that attacks on humans by Serrasalmus rhombeus in Suriname were associated with high densities of piranhas during the dry season, high densities of human prey, agitation of the water by humans, and the spilling of food, fish offal, or blood into the water.

Interactions Between Piranhas and Humans

While Caribe are generally not a threat to humans, there have been cases of interactions between the two. These interactions are often the result of human activities encroaching on piranha habitats, leading to increased encounters and potential conflicts.

In areas where fishing is prevalent, piranhas can be accidentally caught as bycatch. This can result in bites or accidental injuries when handling the fish. Additionally, recreational activities such as swimming or wading in piranha-infested waters can increase the likelihood of encounters between humans and these fish.

To minimize the risk of negative interactions, it is important to understand and respect the natural habitats of piranhas. Conservation efforts and responsible tourism practices can help protect both piranhas and humans, ensuring that these encounters remain rare and harmonious.

Beyond chance encounters, piranhas are also used as a food source for certain communities in the Amazon. Although the fish can be consumed, it is important to adhere to sustainable fishing practices to prevent overexploitation and maintain the ecological balance of piranha populations.

Conclusion

Piranhas are fascinating creatures that have captured the imagination of people around the world. While they have a fearsome reputation, they are not mindless killers or man-eaters. Piranhas are highly adaptable fish with complex behaviors, social structures, and unique adaptations that make them successful predators in their natural habitats.

Understanding the true nature of piranhas and dispelling myths and misconceptions is crucial for appreciating these remarkable fish and promoting their conservation. By respecting their habitats and practicing responsible interactions, we can coexist with piranhas and ensure the preservation of these iconic Amazonian species for future generations.

References

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