Piranha Anatomy
As mentioned, piranha's can be divided into a number of
different genera, all with different visual traits. Members from the genus
Pygocentrus are all recognizable by the convex shape of their head and massive
bulldog-like lower jaw (more powerful and muscular than most
Serrasalmus-species). This reflects their diet: besides being scavengers, if
necessary all Pygocentrus-species are full blown predators as well, that
actively give chase to their prey.
All piranha-species have a powerful, high, thick but laterally
compressed body shape, with keel-like edges running over the upper part of the
body from head to dorsal fin, and on the lower body running over the belly.
Together with a large and powerful large tail and a body covered with very
small scales, their streamlined bodies make them very fast and agile swimmers.
The oddball in the family, shape wise, is Serrasalmus elongatus, the
Elongated or Pike Piranha. This species has a salmon-like, elongated and
slender body, but with the same powerful, well developed tail. It is said to be
the fastest swimmer of all piranha species.
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All piranha-species have a powerful, high, thick but laterally
compressed body shape, with keel-like edges running over the upper part of the
body from head to dorsal fin, and on the lower body running over the belly.
Together with a large and powerful large tail and a body covered with very
small scales, their streamlined bodies make them very fast and agile swimmers.
The oddball in the family, shape wise, is Serrasalmus elongatus, the
Elongated or Pike Piranha. This species has a salmon-like, elongated and
slender body, but with the same powerful, well developed tail. It is said to be
the fastest swimmer of all piranha species.
Unlike many fish-species, piranha's have a small adipose fin between tail and
dorsal fin. This feature is characteristic for the Characin-family, although
members from some other families, like catfish, have an adipose fin as well.
Their predatory lifestyle is reflected by large eyes and a large nose with big
nostrils to maximize the water inflow. They have a very acute sense of smell:
in their natural habitat, murky rivers in South-America, even more darkened by
overhanging vegetation, scent is their main way of tracking down their prey.
Determining the gender of piranha's is considered almost or all together
impossible by most piranha experts, because there are no visible differences
between the genders (in other words, piranha's are not sexually dimorphic). The
general consensus is that the only more or less fool-proof method to sex
piranha's is to observe them during spawning. It is true that adult female
specimen tend to be thicker due to the eggs they carry, it nonetheless is an
unreliable method to tell both genders apart, as well-fed males are often just
as thick.
The only known exceptions to this sexual dimorphism are the Wimpel Piranha (Catoprion
mento), of which males and females are easy to tell apart, and possibly the
Five-Cusped Piranha (Pygopristis denticulata).
