Order Characiformes
Family Characidae
Subfamily Serrasalminae
Genus Piaractus
— Red-bellied Pacu — Piaractus brachypomus [Cuvier, 1818]. Synonym: Colossoma bidens, brachypomum, mitrei, paco; Myletes bidens, brachypomus, edulis, mitrei, paco; Piaractus mitrei, Reganina bidens. (Eng.: Pacu, Pirapatinga, Red Pacu, Silver Pacu). Brazil, Peru, Argentina, Amazon and Orinoco river basins. 40-60 cm. The fish has a flattened body structure, which is entirely covered with small silvery scales. The coloration is bronze-brown with silvery scales and a moiré-black lower half of the body. Adult fish darken significantly and become almost black.
The lower abdomen, chin, pectoral fins, and sometimes the leading rays of the anal fin are colored red. A dark stripe runs along the edge of the caudal fin. Spots are scattered across the body. The male is slightly smaller, with elongated first rays of the dorsal fin and a serrated anal fin. Juveniles are silvery with dark spots, and the sail-like anal fin is carmine-red. When young, they closely resemble juvenile Pygocentrus nattereri.
These fish reach impressive sizes and sometimes decorate large display aquariums. Keeping them requires a species aquarium of very large volumes. At least 100 liters of water should be provided per fish. They are timid and do not like cramped aquariums. This fish is herbivorous, feeding primarily on plant-based food, although it looks very much like a piranha. The preference of these pacus for a plant diet by no means excludes animal feeds. They will quickly rid the aquarium of plants and grow very, very fast — up to two or three kilograms! A multi-ton tank is not at all necessary for this. Even a 200-liter aquarium will yield a quite respectable specimen.
Peaceful fish despite their large size, though they view small fish as lunch. Aggressiveness increases with age. Large gravel is best used as substrate in the aquarium. Only artificial plants should be used for aquarium decoration. The aquarium must have cave-like shelters large enough for the fish to fit inside. Good aeration, filtration, and periodic water changes are necessary.
They eat live and vegetable food (various vegetables, lettuce and dandelion leaves, oatmeal, nettle). You should not constantly feed the fish live food; it should only be supplemental. Sexual maturity is reached at about 3 years of age. They live up to 25 years. pH 5.8-7.5; dH 1-20°; T 22-28°C.
Identification: Red-bellied Pacu — Piaractus brachypomus.
Genus Ossubtus
The genus Ossubtus is closely related to the genus Mylesinus, differing only in teeth. Kept in aquariums: — Ossubtus xinguense [Jegu, 1992]. Brazil, Xingu River. 17 cm. Females behave aggressively towards other females. They feed mainly on plant matter and frozen foods. T 22-25°C.
Genus Pristobrycon
— Speckled Piranha — Pristobrycon striolatus [Steindachner, 1908]. Synonym: Pristobrycon baratai, Serrasalmus, Pygopristis antoni, Serrasalmus striolatus. Brazil, Venezuela, Guyana, Amazon and Para rivers. 15-18 cm. Body diamond-shaped, silvery with an orange tint and rare black dots, with a red lower jaw. Adults have a small spot on the cheek. The base of the adipose fin is very dark. Fins are orange-red (especially the anal fin, which is also more curved in the male), the root and outer rays of the tail are black. The edges of the caudal fin rays form a black “V” shape.
Brazilian species have a reddish-orange tint, while those from other waters may be golden-yellow. A strict hierarchy is maintained in a piranha school. Juveniles are sometimes kept together, but as they mature, their natural behavior develops rapidly, and they should not be kept in groups. It is recommended to keep single adults in species aquariums. They nip the fins of other fish. Undemanding regarding water parameters. Filtration, aeration, and weekly water changes are needed. Lighting is diffused and dim.
Genus Pygopristis
— Big Toothed Piranha — Pygopristis denticulata [Cuvier, 1819]. Synonyms: Pygopristis fumarius, Serrasalmus denticulatus, punctatus. (Eng.: Big Toothed Piranha, Lobetoothed Piranha, Pirambeba). Brazil, Peru, Venezuela, Orinoco River. 20 cm, in the aquarium up to 15 cm. They have unique, specialized teeth that help remove the skin from seeds and fruits.
The body is silvery-bluish, with possible dark spots and stripes, and lemon or red fins. Usually, the upper part of the body has a bluish tint, while the lower part and the base of the caudal fin are yellow or orange. Adults may acquire dark brown colors. Dorsal, anal, and caudal fins have a lemon tint with a grayish-white border.
Unlike many other piranha species, they can be kept in groups. Carnivorous by nature, they feed on small fish; because of this, it is better to keep them singly, or if tank size permits, in a small group. They should not be mixed with other piranhas as they might eat them. The aquarium should contain shelters among roots and stones, as well as plenty of plants. They are fed bird seeds, fish fillets, frozen fish, shrimp, krill and other crustaceans, earthworms, tubifex, bloodworms, pellets, flakes, fruits.
Pygocentrus cariba, Pygocentrus nattereri, Pygocentrus piraya.
Mylossoma aureum, duriventre, Myloplus rubripinnis, Myleus schomburgkii, ternetzi. 
