Kner, 1858. Characiformes, Characidae, Serrasalminae .
Common Names: Red Belly Piranha, Red Piranha, Red Bellied Piranha.
Environment: Pelagic; freshwater;
Description: D 16-18; A 28-32; l.lat. 85-100; 24-31 scutes in ventral keel. Gill rakers of the outer branchial arch elongate, hooklike. The number of gill rakers posteriorly on the first arch (total 8-15 in Pygocentrus). Body very deep and strongly compressed; edge of belly serrate. The height of the body is nearly one-half of the total length (without caudal); snout very obtuse and short; lips fleshly; the width of the interorbital space is a little more than one-half of the length of the head; the second infraorbital bone touches the preopercular limb. The anal and dorsal fins are set well posterior and the adipose fin is present (it always remains a rounded lobe); caudal fin distinctly forked; anal fin-base long, in old individuals fin produced to a point anteriorly. Scales small ( 2-3 mm). Piranhas have a single row of sharp teeth in their upper and lower jaws. These teeth are tricuspid (three points) with a large, triangular blade-like middle cusp. Extremely sharp, the teeth are tightly packed and interlock, making them excellent for puncturing and shearing flesh. Coloration very variable, depending on age and environmental the body-depth and form of the head likewise change with age. Healthy, 10-15 cm. long fishes are blue-grey to brown-grey on the back; flanks pale brown above to delicate olive, silvered with numerous tiny metallic spots; underside, including the keel and belly, pectoral and ventral fins and and anterior part of the anal, gleaming cinnabar to blood-red ; dorsal and caudal fins dark, the latter with a pale inner field ; anal fin red with a broad black margin. Total length up to 33 cm, body weight up to 3.5 kg.