Piranhas & Pacus

The sheep pacu, Acnodon normani, is a serrasalmid from Brazil, possibly restricted to the Xingu and Tocantins watersheds of the Amazon basin. Also known in the trade as 'tiger pacu', it is often said to be a frugivore or herbivore, but aquarium observations suggest it also feeds on the scales of other fishes. That makes it unsuitable for the community aquarium, although it does not seem to target much smaller species.

The spotted metynnis, Metynnis maculatus, is a silver dollar probably confined to the upper rio Madeira and upper rio Paraguai in Bolivia and Brazil. It is most often confused with M. argenteus and M. lippincottianus, but it has more midlateral scales and more spines on the ventral keel than either. It schools in nature and needs a very large tank with a group of six or more.

The black-barred myleus, Myleus schomburgkii, is a close relative of the redhook from parts of Venezuela, Peru and Brazil. The black vertical bar on the flanks distinguishes it, and it is a smaller adult fish, though it is sometimes offered for sale as a redhook. Also called the black-ear pacu and disc pacu, it should be kept in groups of at least five, and a tight-fitting lid is a good idea as it moves extremely quickly when startled.

The white piranha, Serrasalmus brandtii, may be restricted to the rio São Francisco watershed in eastern Brazil. Also known as 'green piranha' or 'Brandt's pirambeba', it appears infrequently in the trade, and its name is sometimes misapplied to the distantly related Pygopristis denticulata. Adults are uniformly golden-bronze with dark fin margins and a concave head profile above the eye. It is best kept alone as a single specimen.

Goulding's piranha, Serrasalmus gouldingi, is a deep-bodied piranha from the rio Negro drainage in Brazil and the Casiquiare system in Venezuela. It occasionally appears in the ornamental trade, sometimes as 'blue tiger piranha'. The eye is bluish or coppery, the body carries vertically-elongate dark spots and the caudal-fin has a blackish basal band. Its native rivers are acidic, mineral-poor blackwater, and it is best kept alone.

The piraya, Pygocentrus piraya, is a piranha restricted to the rio São Francisco watershed in eastern Brazil. It can be identified by bright yellow-orange pigmentation on the lower jaw, opercle and flanks in life, and larger specimens have rays in the adipose fin. It is best maintained alone because mature individuals are reported to be extremely aggressive towards one another when space is limited.

The pike piranha, Serrasalmus elongatus, is a streamlined piranha from the Amazon and Orinoco basins in Venezuela, Ecuador, Peru, Bolivia and Brazil. Its elongate shape is unique among serrasalmids and makes it possibly the easiest Serrasalmus to identify, although large adults fill out into a more diamond-shaped figure. Known as 'caribe pinche' in its native countries, it is a rare find in the trade and suits only the enthusiast as a specimen fish.

Géry's pirambeba, Serrasalmus geryi, is a piranha from the Rio Araguaia and Rio Tocantins drainages in Brazil. Sometimes sold as the 'violet-line piranha', it is one of the easiest Serrasalmus to identify because the purple stripe from the lower jaw over the top of the body is unique to it. S. compressus has been sold as S. geryi, and reports of it living in groups are considered tenuous, so it is kept as a specimen fish.

Serrasalmus maculatus, the mac, is a piranha from the Amazon, Paraguay and Paraná river systems, described from the rio Guaporé in western Brazil. It grows to a manageable size, is relatively hardy and is sometimes called the 'gold piranha' or 'golden mac' in the hobby. It has often been confused with S. spilopleura, and it should be considered a specimen fish that does not make a good tankmate for anything else.

Serrasalmus marginatus is a piranha from the Rio Paraguay and Rio Paraná drainages in Brazil, Paraguay, Uruguay and Argentina. Its main distinguishing feature is the thick, black, v-shaped marking in the anterior portion of the caudal fin, and it is rarely seen in the hobby. Individuals defend feeding territories in the wild, and conspecifics are liable to fight until only one remains, so it is kept singly as a specimen fish.

Sanchez's piranha, Serrasalmus sanchezi, is a small piranha endemic to Peru, collected from rivers including the Ucayali, Itayi and Pacaya. It is sometimes still sold as 'Spilo cf' or 'Ruby-red Spilo', and its red throat has led to confusion with S. medinai and even Pygocentrus nattereri. The serrae on the underside are arranged irregularly, unlike other Serrasalmus. Whether it can be kept in groups remains hotly debated.

Serrasalmus serrulatus is a piranha reported from Peru, western Brazil and Argentina. The validity of that range is unclear, since the name may have been applied to more than one species. It also occupies a particularly confusing taxonomic position within the 'humeralis group' and is very close in appearance to S. eigenmanni, S. hollandi, S. humeralis and S. nalseni. Its habitat is unknown. Conspecifics are liable to fight until only one remains, so it is a specimen fish for the enthusiast.

Serrasalmus altuvei is a piranha from the Venezuelan section of the Rio Orinoco basin, where it lives in the clear, sunlit waters of the Llanos. Very scarce in the hobby, it turns up mostly among imports of juvenile S. rhombeus and is also known as 'caribe azul' or 'blue caribe'. It belongs to the 'compressed group' and can be very tricky to tell from S. compressus, though juveniles supposedly differ in having speckling only on the upper half of the body.

The wimpel piranha, Catoprion mento, is a scale-eating fish from Colombia, Venezuela, Guyana, Brazil and Bolivia. Though not a true piranha, it resembles them and is quite closely related to Pygocentrus species. The common name comes from the German 'Wimpel' (banner), after the extensions to the leading dorsal-fin rays in mature fish. Adults are best housed alone, and it is sensitive to poor water quality and to swings in chemistry.

The black pacu, Colossoma macropomum, is a very large serrasalmid from the Orinoco and Amazon basins in Colombia, Venezuela, Peru, Bolivia and Brazil. Known as the tambaqui in its native countries, it is the second largest scaled fish in the Amazon basin and easily capable of reaching 60 cm in captivity. It is regularly sold as a small juvenile, and releases of outgrown fish have led many wildlife authorities in the US to ban its sale. Wild stocks suffer from gross overfishing in many of its native waters.

Metynnis argenteus is a silver dollar, a relative of the piranhas probably endemic to the Rio Tapajós drainage in Brazil. It is very similar to M. hypsauchen, and both are sold in the hobby as 'silver dollar'. The two are virtually identical in appearance and care, but M. hypsauchen has a black blotch above and behind each eye. An avid plant-eater, it is best kept in a group of at least five and may eat much smaller fish.

The silver dollar, Metynnis hypsauchen, is a relative of the piranhas with a patchy distribution in Guyana, Brazil, Peru and Bolivia. Sometimes called the plain metynnis, it is sold under the same name as the very similar M. argenteus and differs in the black blotch above and behind each eye. A striped form is not a distinct species. An avid plant-eater, it is best kept in a group of at least five.

Metynnis lippincottianus is a spotted silver dollar from Brazil and French Guiana, found in the lower and middle Amazon and the Oyapock system. It is occasionally seen for sale, sometimes as 'silver dollar', and its spotted pattern tells it apart from M. argenteus and M. hypsauchen. The spots are less pronounced than in M. maculatus, with which it shares a common name. The precise extent of its range is unclear.

The redhook, Myloplus rubripinnis, is a relative of the silver dollars from much of northern South America, including the Amazon and Orinoco. Commonly sold as a silver dollar, it can be told apart by its black-trimmed, red anal fin and grows much larger, to around 25 cm. Given a large enough aquarium, correct feeding and good water quality it should not pose many problems. It is still widely referred to as Myleus rubripinnis.

The red-bellied pacu, Piaractus brachypomus, is a serrasalmid from the Orinoco and Amazon basins in Colombia, Venezuela, Peru, Bolivia and Brazil. Known as the pirapitinga in its native countries, it is one of the largest scaled fishes in the Amazon basin, with wild fish recorded to 88 cm. Juveniles mimic the red-bellied piranha and are sold small as 'vegetarian piranha', and releases by aquarists have left populations in the USA and elsewhere.

The black spot piranha, Pygocentrus cariba, is restricted to the Río Orinoco basin in Colombia and Venezuela. Many of its habitats lie within the llanos, and it has been recorded from river channels, tributaries and floodplain lakes, many of them acidic blackwater environments. Specimens over 100 mm SL have a large humeral spot and few spots on the body, which separates it from P. nattereri. It is best maintained alone.

The red bellied piranha, Pygocentrus nattereri, occurs through much of the Amazon basin and south into the Paraná and Uruguay river systems. Famed as a rapacious predator, it is among the most notorious freshwater fishes in the world. According to Herbert Axelrod (1976), the myth began with a feeding frenzy staged for Theodore Roosevelt in Brazil in 1913. Usually only juveniles form aggregations, and the species is relatively easy to breed in the aquarium.

Serrasalmus rhombeus, known as the black piranha or rhom, is a large piranha recorded from much of northern South America. It occurs in numerous geographical forms that vary in size, body form and colour, linked by the deep red eye of mature fish, and a species complex has been suggested. Juveniles lack the red eye and are easily mislabelled. Conspecifics fight until only one remains, so it is kept alone.

Serrasalmus manueli, sometimes sold as the 'green tiger piranha', is a piranha from parts of the Amazon and Orinoco basins in Brazil and Venezuela. Adults are caught in deep, flowing sections of major river channels and grow to 435 mm SL. Imported fish are notoriously sensitive travellers with high mortality, and this is a species for the specialist that must be kept alone, since adults fight until only one remains.