just to clear up the mis-information here a red tailed payara does not = hydrolycus Armatus. A red tailed payara is a hydrolycus Tatauaia and a armatus is another hydrolycus species as well but it is alot different in size and temperment than a Tatuaia. The picture you have up there is a armatus payara. A redtailed Tatuaia looks like this and they get to about 18'' or so. And grow very slowly.