[dave mcg]

this is a very old rhom and about 12 inches long.its a confident fish with great looking protruding teeth but iv never known exactly what type he is.can anybody help

 

[Judazzz]

That's a Serrasalmus rhombeus - pain and simple. An awesome-looking one, I might add

What variant it is cannot be guessed from just watching at a picture - you need to know where it was collected.
And a common name based on how the fish looks makes no sense either - anyone can slap a name tag on a fish based on what he sees. It holds no value whatsoever, though.

 

[marco]

very nice rhombeus,