Characteristic , however , is a blue-gray to brownish dorsal coloration , with a paler shade and a silvery luster on the flanks . In fry and juvenile specimens the throat , abdomen , and pectoral , ventral , and anal fins are bright vermilion . This coloration fades with increasing age , however . The species is generally regarded as being very aggressive . It is possible that the remaining piranhas described here as synonyms , color varieties , local races , or subspecies of Serrasalmus nattereri .
Numerous investigations carried out by the author indicate otherwise , however .
For this reason it is suggested here for the first time that Serrasalmus nigricans be classified as a species in its own right . Where Serrasalmus notatus is concerned , the reader is referred to the South American literature already available . 25-28 teeth on the ventral keel . The body is similar in shape to that of S.nattereri , but the head and jaws are daintier in build . Juvenile coloration is silvery with numerous black spots .