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Captain Britannia
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serra's just seem to have a more elongated mouth than pygo's who have a blunt shape to the haed the easy way to describe is concave /convex but looking at my reds even though they are blunt headed they still have a slight concave bit between eyes ,i think different broods will have slightly different shapes to them not all look exactly the same a bit like humans
 

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Natts are members of the genus pygocentrus. According to OPEFE there is no such thing as Serrasalmus Nattereri. This is an example of another site giving out misinformation. Visit OPEFE for the best information on the classification of piranhas. This site will be opening up its own sections (heavily based on OPEFE) in the very near future to aid hobbyists in recognizing the different types of piranha.

I could be wrong on this though, I just got my info from OPEFE, maybe frank or one of the other experts here could clarify further?
 

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When thinking about convex and concave head shapes the difference is very clear when comparing two pictures:


Pygocentrus Cariba


Serrasalmus Rhombeus

The way Ive always looked at it is how the forehead of the pygos round outward around the eyes and continue on to the mouth. Serras round inward before the mouth. I could be wrong on this but this is how Ive always looked at it. Of course, convex and concave head shape is not the only determinent of species, just one characteristic.
 

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Bare in mind that the concave profile above the eyes is found primarily in juveniles and young adults of all species. With very old piranas (such as S. rhombeus) they are very convex profile to the point of looking like a Pygocentrus. Only in home aquarios do tank raised piranas tend not to have a massive dorsum because of diet and lack of certain vitamins found only in nature. That is why you see many of the wild caught appear different when compared to same species raised in aquarios.
 

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"The Dancing Banana Man"
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hastatus said:
Bare in mind that the concave profile above the eyes is found primarily in juveniles and young adults of all species. With very old piranas (such as S. rhombeus) they are very convex profile to the point of looking like a Pygocentrus. Only in home aquarios do tank raised piranas tend not to have a massive dorsum because of diet and lack of certain vitamins found only in nature. That is why you see many of the wild caught appear different when compared to same species raised in aquarios.
hmmm thanks
 

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It should also be noted that it really wasnt misinformation, it was a matter of being out dated information. Nattereri used to be classified as Serrasalmus before Dr. Fink revised the twp genus several years back
 

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It should also be noted that it really wasnt misinformation, it was a matter of being out dated information. Nattereri used to be classified as Serrasalmus before Dr. Fink revised the twp genus several years back
Actually you are quite mistaken on several of your points above. P. nattereri was ranked as a subgenus Taddyella nattereri (Gery, 1972, 1977). Antonio Machado-Allison (1985) revised the group in its original Eigenmann (1915) placement of 4 genera. Fink had little to do with the placement as you describe. He revised the genus Pygocentrus only by naming 3 species and providing a key. Prior to this several other authors also broke the group up, some reestablishing the original placement, others using the Norman 1929 lumping.

The misinformation that you say didn't exist, actually did when Gery said there were only 17 species of piranas in all of South America.
 
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