About piranhas in aquarium – and not only there (part 2) – Paweł Czapczyk, PhD

For nearly 40 years a passionate aquarium and terrarium hobbyist, writer, editor and breeder; organizer of exhibitions and conferences on aquarium and terrarium hobby; author of many books and press articles, as well as radio broadcasts and screenplays for documentary films; nature photographer, editor-in-chief of “Aquarium Magazine”.

In old stories of travelers who reached the Amazon, we can read about many brave wanderers who had the courage to venture deep into the Amazon basin and who were attacked by bloodthirsty piranhas.

However, in reality only some of the piranhas, especially from the genera Pygocentrus and Serrasalmus, the so-called proper piranhas, can be considered real danger to humans. They are famous for their predation and group attacks on their prey.

PYGOCENTRUS NATTERERI (KNER, 1858) – RED-BELLIED PIRANHA, RED PIRANHA The red piranha is a legendary animal. This fish is emblematic of the family Serrasalmidae and responsible for the reputation of the entire group. It has the look of a born killer. With a protruding and swollen mandible and an ominously immobilized upper jaw, it can be frightening. Its mouth houses an impressive row of teeth, as if designed to instantly tear through tough skin and bite into the soft tissues of the victims. The incredibly sharp, hard and conical teeth (characteristic of carnivorous piranhas) leave relatively large and blood-broiling cavities in the flesh. The red piranha can reach 50 cm in length. But only in natural biotope, in aquariums the largest specimens are usually around 30 cm long. The species’ home is the South American queen of rivers, the Amazon River, along with its tributaries. It can also be found in the watercourses of northeastern Brazil and in the Parana, Paraguay and Essequibo basins. Like any predator, it has incredibly sharp senses. It gets excited by blood spreading through the water, even if it is in great dilution. The aroma of blood

Pygocentrus nattereri

Picture of Pygocentrus nattereri

causes the red piranha, which we thought to be a lazy and sluggish animal that lives in the lower parts of the tank, to transform into a bloodthirsty beast. Each abnormal movement in the water like a bird falling into the river, or a human swimming and splashing through the water, or even another piranha entangled and fluttering unnaturally among the plants, can stimulate similar behaviour. Some local Indians insist that only an open wound from which lymph and blood are oozing is likely to stimulate piranhas to attack. Others rub their bodies with an extract of tropical herbs just before bathing or working in the river. Some tribes from the Amazonian are also known for purifying mourning rites involving immersing the corpse of the deceased in water ”boiling” with piranhas. The remains, stripped down to their skeletons, are then buried in the ground by the natives. Lovers of this species sometimes use in their tanks solutions, which might seem surprising for amateurs. Along with the school of adult piranhas, they keep a few dozen/hundred neon tetras. How is it possible that colourful Characiformes are not attacked? An old theory, mentioned in many aquarium guides, suggested that the light reflected by fluorescent fish causes fear among predators. Nowadays it is rather believed that neon tetras get ”unnoticed” because they are an overly microscopic snack. Similarly, in the tanks of a public institution that I am friends with, wild Mexican cichlids of the

Chapalipchthys pardalis species, much larger than neons, coexist peacefully with piranhas. Aggressive reactions, on the other hand, can (and often do!) occur within the same species. Starved piranhas can easily pick a fight, attacking not only the weakest specimen, but biting each other as well. The protruding parts of the body are particularly vulnerable to attack, namely the fins, the back and the ventral region. It also happens that in the amok of catching prey, lips and mouth parts are also bitten off. Fortunately, as long as we do not forget about abundant and regular feeding, the defects get quickly reconstructed, the gouged places get healed; with only scars left, which are, humorously speaking, a field of work for the aesthetic doctor. You should remember no to introduce other, slightly smaller specimens to tanks with piranha, because their fate seems to be sealed. And it is important to follow basic safety precautions when feeding fish and doing any cleaning in the aquarium. Some aquarists wear special wire gloves to protect their hand and forearms. Others approach the fish (which have been amply fed before) with calmness, but closely observe the situation in the tank. This is because, in general, piranhas are timid. They react with fear to sudden movement in front of the aquarium or sudden illumination of the tank and that’s why it is recommended to use lighting with simulation of sunrise and sunset. During the desludging process, fish can lie side by side in sand or hide behind plants in the darkest corners. On the other hand, when kept alone and having only large cichlid fish for company, piranha appears to be a docile and harmless animal. But in such a configuration when the fish is a „single”, it neither hides well nor can its characteristic natural behaviours be observed. Pygocentrus nattereri is a social fish leading a hierarchical life in the watercourses of Amazonia. In home tanks, this fact should be respected and the species should not only be provided with adequate living space (the minimum tank capacity is currently considered to be 500 liters, while the minimum length should not be less than two metres) but also kept in groups of at least 6-7 individuals. Of course red piranhas show their original beauty only in a school consisting of a dozen or so representatives of their own species, swimming in aquariums that decorate hotel lobbies, shopping malls or gracefully arranged large living rooms in homes. Such tanks (about a dozen

Snails of the species Melanoides tuberculata, eating food scraps, prove very useful in tanks with piranhas

thousand liters in volume each) allow not only to properly arrange the interior and take care of proper water parameters, and then maintain the whole at a stable level, but also to be consistent with modern lifestyle at one hand and the principles of biotope aquaristics on the other. Fish will feel best in clean, well-oxygenated and efficiently filtered water. Over-filtration achieved with a sump or at least two large canister filters is not only advisable but indispensable. Why? Because it is rightly assumed that all piranhas are particularly ”messy” fish, not only do they eat sloppily, but they have fast metabolism as well. Thus, they can contribute to significant water quality degradation in a short period of time. To ensure correct development and coloration of the fish you need to provide slightly acidic (within 5.5-7.5 pH) and soft (from 6 to 10°dH) water with a minimum concentration of nitrates. However, it is possible to keep red piranhas (apart from the spawning and breeding season) in water that is much harder, even up to 20°dH. The water temperature should range from 23-28°C. As a substrate you can use both fine sand and gravel. The tank should be arranged to provide plenty of free space, hiding places made of roots and branches and with strong and sturdy plants growing in clumps in its corners and along the back wall of the aquarium. The plants can include tape grass, bacopa, lesser water-plantains, cryptocorynes and Thai onion plants. The light should be moderate and diffuse as excessive lighting of the tank will increase the stress of fish and enhance their natural skittishness. Everyone knows that the red piranha is a declared carnivore. However, not everyone suspects that these fish are actually food opportunists, also eating seeds, nuts and fruits in the wild, depending on the season. In an aquarium, these fish can be fed with both live and frozen food (but in room temperature).

Adolscent piranhas must be kept in a group of individuals of the same size

Other appropriate foods include whole fish and large fillets, and occasional poultry, horse meat, and beef. After all, piranhas lurking in South American rivers sometimes pose a threat to livestock coming down to the watering hole, as well as wild tapirs or deer. This situation occurs especially during droughts, when starved fish are cut off from the mainstream in shallow backwaters. It should be remembered, however, that excess lipids from warm-blooded animals are not metabolized properly and may be deposited in internal organs, leading to their damage. The best food for the young is obviously fish meat. However, feeding with small carps and goldfish carries the risk of parasites. It is a good idea to occasionally serve krill, shrimp, clams, common earthworms or European nightcrawlers. A high-protein granulated food with spirulina (which I have tried successfully myself) works well as a dietary supplement, but piranhas need to get used to feeding dry food. Red piranhas reach sexual maturity in an aquarium when they exceed about 15 cm (often even earlier) and they are the most frequently reproduced members of the Serrasalmidae family by breeders! The spawning tank must not be too small. Best results are obtained when a parent pair can match spontaneously within larger group of fish. The nesting territory chosen by the male and the female is immediately and fiercely defended. At this time it is advisable to darken the aquarium a bit, and to oxygenate the water more intensively. The male digs a hole in the sand and the female lays up to several thousand eggs, usually stuck to plant roots, from

Two-month-old Pygocentrus nattereri with visible fi n loss

which the larvae usually hatch after 2-3 days. The fry fed several times a day with zooplankton grow quite rapidly but unevenly. Initially the male takes care of the offspring, sometimes the female supports him in the effort of upbringing. However, acts of cannibalism among adolescent fry (if we do not start separating the juveniles according to size in time) seem to be inevitable.

PYGOCENTRUS CARIBA (HUMBOLDT, 1821) Although Humboldt described this piranha as early as the third decade of the 19th century, it is still commonly confused with Pygocentrus nattereri, and some breeders and ichthyologists even consider it to be its subspecies. Either way, Pygocentrus cariba can be found in the Orinoco River basin of South America within Colombia and Venezuela. It is most often spotted in acidic, tannin-rich, and mineral salt-poor „black waters” where it does not usually exceed 28 cm in length. Like the red piranha, it has a stocky body that is strongly laterally fl attened, and teeth that are pointed and conical, serving both to bite off bites and to crush food. In addition to fi sh, it eats invertebrates, seeds, fruits and green shoots of plants. Tank residents should be fed a mixed diet with a predominance

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of animal proteins: fi sh fi llets, shrimp, earthworms. In addition, it is worth enriching their diet with proteinrich granules with spirulina. A spacious aquarium should be set up and equipped the same as in the case of Pygocentrus nattereri (preferably sandy substrate, decoration with branches and roots, partial stocking with hardy plants, but also

Picture of Pygocentrus cariba

leaving free swimming space). Over-filtration is also necessary, preferably in the form of a sump or bucket filters. The water should be additionally changed every week (up to about 40% of the tank volume). The water pH should oscillate between 4-7 pH and the temperature should be kept between 22-28°C. It is recommended to keep the species in a group of at least several specimens. However, in especially large tanks Pygocentrus cariba can successfully live with Pygocentrus nattereri.

PYGOCENTRUS PIRAYA (CUVIER, 1819) – PIRANHA This is third piranha of the genus Pygocentrus, which is considered by some sources to be the most dangerous member of the family Serrasalmidae. Some experts believe that this fish, penetrating all parts of water, is also the strongest of all piranhas in the world. A muscular head with a high forehead and strong jaws immediately betray adaptation and food specialization. So does its mandible, which is thick and protruding and its extremely sharp teeth. A healthy fish could easily bite off an adult’s toe or hand. Is this ”beast” beautiful? Here, opinions are divided. There are times when its ventral yellow-orange or fiery red body part, which when confronted with a darker silver-black back with lighter mottling, will take the breath away in someone looking for offbeat colour solutions. Pygocentrus piraya reaches a maximum length of 35 cm in the aquarium, although in the wild spe- cimens even over 50 cm have been observed. The first English name, Gold Piranha, refers to the qualities of the fish; the second, San Francisco Piranha, indicates the primary location of the species, which is limited in South America primarily to the Rio São Francisco and its tributaries. One can also come across the common name ”Piraya Piranha”, as well as the catchy marketing term ”Man-Eating Piranha”, which leaves no illusions as to the nature of this genre. When starved, these fish can be particularly fierce and aggressive. They can react similarly furiously when exposed to stressors. Some data tell of many,

sometimes massive, attacks on humans, however they have never been fully corroborated. Pygocentrus piraya is obviously a definite carnivore. But, in addition to fish, it also eats large insects and almost anything that comes near its mouth. It will also not disdain plant foods from time to time. In the aquarium it eats fish and fish fragments, shrimp, crabs, squid and krill. Occasionally, you can feed it with frozen chicken and mice. If it is gradually accustomed to ready-made foods, it will also consume high-protein granulated feeds, but these should be fed in moderation. Breeding ”Man-Eating Piranha” in an amateur aquarium is not easy, as fratricidal mutilation and acts of cannibalism can occur in a group of kept fish. It is highly likely that an accidentally bitten or injured fish will attract the attention of the rest of the stock and will end its life torn apart by the others. The smallest member of the group may face similar aggression. And it may happen that from a shoal of a dozen or so fish, at the end we will be left with only the biggest and strongest one. Although the fish become statistically more tolerant as they age, they are strongly territorial during the spawning season. Some U.S. breeders recommend keeping individuals in a mixed school of mostly Pygocentrus nattereri representatives, but this is not a view that replicates the natural environment, as the two taxa, although closely related, are not found together in the natural biotope. The recommended aquarium capacity for Pygocentrus piraya is 1000 litres or more. The fish is quite tolerant of the chemical parameters of typical tap water so you can start with 6-7.5 pH (in the Rio São Francisco basin, the water pH varies between 4.8 and 8.7 pH). It tolerates hardness above 20°dH well, while the temperature should be kept at 21-24°C, and should be raised only slightly for the breeding season (then it is also good to lower the pH). The water in the tank should be efficiently filtered and

Serrasalmus rhombeus

aerated, as well as regularly refreshed, as this will significantly improve the mood of the fish and reduce their aggression. It is best to use a sandy substrate and decorate the interior with roots and the background and sides of the aquarium should be planted with clumps of hardy plants. The mating habits of this species resemble those of Pygocentrus nattereri. However the female, which is usually staying in deeper parts of the river, chooses shallower area with sandy bottom for spawning. The fishermen of the Rio São Francisco who wade in the river often bear on their feet and hands the marks of ”close encounters of the third degree” with the fierce and ferocious fish that guard the eggs and newly hatched fry. Their limbs are marked with sickle-shaped scars, characteristic reminders of the razor-sharp teeth of piranhas. Human encroachment on the environment has caused significant population depletion and, at present, importation of this species from some South American countries is prohibited. On the other hand, well cared for and wonderfully colored they are an unquestionable decoration of large exhibition aquariums. And as such, they are finding an ever-growing group of enthusiasts who are willing to devote all their free time to them.

SERRASALMUS RHOMBEUS (LINNAEUS, 1766) – THE REDEYE PIRANHA, ALSO KNOWN AS BLACK PIRANHA, WHITE PIRANHA, SPOTTED PIRANHA OR YELLOW PIRANHA The characteristic features of this species include a distinctively beveled, rhomboid body, sharply defined dorsal and anal fins, and a black-edged caudal fin. In aquariums, this fish struggles to reach 35 centimeters in length while in the wild it can be even 20 centimeters bigger. Some researchers maintain that the ”true” Serrasalmus rhombeus is found only in Guyana and suggest that this taxon needs to be more thoroughly studied and revised in systematics. However, most ichthyologists assume

that the range of all species varieties extends from the Amazon and Orinoco rivers and their tributaries, through the coastal watercourses of northeastern Brazil, to the eastern and northern rivers of Guyana. The also claim that the individual populations (Guyanese, Brazilian, Venezuelan, or Peruvian) differ only in coloration. This species is considered a behavioural opportunist as it is characterized by high adaptability and tolerance to various chemical parameters of water. It feels good not only in habitats with soft and black water, but also in typically white and quite hard waters. This should make aquarists happy as spotted piranha does not have high requirements to the chemical composition of water and meticulous correction of its parameters is not necessary. The arrangement of the interior of the tank and the type of decorations used is a secondary matter as well. You can use either rocks and stones (white waters), or roots and leaves of beech, oak or ketapang lying on the bottom (black waters). Serrasalmus rhombeus is a shy fish at first sight, but with age the level of aggression in specific individuals clearly increases. The bite force of this piranha may seem shocking as according to some sources, it is comparable to the jaw pressure of a white shark! That’s why it must have been really surprising when in 1977 a stock of these piranha was discovered in the pond of an abandoned amusement park in the Miami area. Ichthyologists alarmed that the fish, most likely released by an extremely irresponsible aquarist, overwintered in Florida. However, in its homeland, this fish is sometimes caught by fishermen with fish bait. However, the menu of this species is much richer. Serrasalmus rhombeus preys on fish, small mammals, crustaceans, lizards, beetles and other insects; and sometimes even carrion. This should be taken into account by the aquarists who need to make sure that fish’s diet is as varied as possible by including high-protein granules in the menu. Some breeders

feed mostly with beef hearts but I personally don’t consider it obligatory. I believe that best food includes fish parts (with skin and scales), crab meat, and shrimp. From a purely moral point of view, it may seem questionable to give live fish (goldfish or large livebearers from our own breeding), but it is an action that is completely in line with the natural needs and hunting instinct of this species. However, feed fish should be quarantined beforehand. This predator rushes greedily at its prey, tearing it apart. Then the food particles float in the water, generating an increase in the concentration of nitrogenous substances. Good water aeration and, above all, effective and efficient filtration (over-filtration!) are therefore basic requirements for successful breeding. Fish should not be disturbed without reason, for example, by tapping on the glass. Care must also be taken when feeding, changing water, and desludging the bottom. Remember that the skin on your hands must be free of wounds and fresh cuts from which blood would ooze. Before any maintenance inside the aquarium, you should also make sure that the fish are well fed. Under certain conditions, Serrasalmus rhombeus can become dangerous to humans. Cases of fierce attacks and serious bites have been reported in Suriname, among other countries. In the wild, the redeye piranha can be found living solo or in groups. However, it is most often seen grouped in loose shoals. In the tank be wary of keeping more than one individual in the aquarium, whether a juvenile or adult. Only very experienced growers can afford such an experiment. After all, it is not a sociable fish, able to lead a peaceful and harmonious existence with other members of its own

species. Sooner or later there will be a fratricidal fi ght to the point of extinction, consisting of biting each other’s fi ns and eating out scales. In an aquarium Serrasalmus rhombeus grows quite slowly, but is characterized by its longevity. It can live up to about 28 years.

SERRASALMUS MANUELI (FERNÁNDEZ-YÉPEZ & RAMÍREZ) Not entirely researched, yet fascinating representative of the subfamily Serrasalminae is Serrasalmus manueli, which is very rarely found in both private and public tanks. This strong and agile swimmer and aggressor with needle-sharp teeth is native to the Amazon and Orinoco basins (inhabiting the waters of northern Brazil and Venezuela). It can be spotted in the Rio Negro, Rio Xingu as well as Rio Cassiquiare, Rio Atabapo and Rio Cunucunuma tributaries. It can reach nearly 50 cm in length (according to some sources even 55 cm, and according to local fi shermen as much as 60 cm), but specimens of this size are practically unheard of in aquariums. It requires an eminently meaty but varied diet, although in the wild it also eats food of plant origin. It shows great environmental adaptability. In the wild it can be found in both black water and river biotopes characterized by high transparency (White Water). It does not avoid the main sections of rivers with fast current, sunny shallows with lush vegetation, or slow-moving or meandering watercourses in the middle of dense tropical jungle. As it grows and reaches sexual maturity, the shape of the fi sh changes slightly, and the coloration of the gill cover changes from shades of silver and metallic celadon, through yellow and orange, eventually changing to a distinct fi ery red. So far, this species, like many other members of the family Serrasalmidae, has not been successfully propagated in an aquarium.

Photos: Paweł Czapczyk