Scientists working on the molecular phylogeny of piranhas (Serrasalmidae) have found molecular data to be useful in distinguishing the species.
In a study published in a recent issue of the journal Zootaxa by Barbie Freeman, Matthew Osentoski and Timothy Collins of Florida International University, and Leo Nico and Howard Jelks of the United States Geological Survey, the molecular systematics of the piranha family (Serrasalmidae) were examined using sequences for three mitochondrial genes.
The results of their studies show that molecular data was useful for identifying species of piranhas where traditional methods have encountered difficulties.
Piranhas are traditionally difficult to identify from external morphology, because of changes in colour pattern as the fish grows, and differences in colour due to habitat.
"A wide range of neotropical fishes occurring in black- or tannin-stained waters tend to be very darkly colored whereas in white- or muddy waters individuals are much lighter.
"Such differences are often much greater than the subtle color differences used by some ichthyologists to differentiate purported new species.
"Consequently, we suspect the influence of water type on phenotype (i.e. intensity and pattern of pigmentation) has contributed, on occasion, to erroneous new species descriptions."
The study also hints at future changes in the taxonomy of piranhas, as both Serrasalmus and Pristobrycon were not found to be natural groups: "If the term piranha is to refer to a monophyletic clade, it should be restricted to Serrasalmus, Pygocentrus, and Pristobrycon (in part), or expanded to include these taxa plus Pygopristis, Catoprion, and Pristobrycon striolatus."
The biogeography of the group was also studied, with the analysis from this study suggesting that the piranhas are a much younger group (diversifying at 1.8 million years ago) than previously thought.
For more information see the paper: Freeman B, LG Nico, M Osentoski, HL Jelks and TM Collins (2007) " Molecular systematics of Serrasalmidae: deciphering the identities of piranha species and unraveling their evolutionary histories. Zootaxa 1484: 1"38.