By the way, those pictures that were posted above are of Black Pacus (generally identified as Colossoma macropomum). They are known to grow much larger than the Red-Belly Pacu (Piaractus brachypomus). Still, RBPs will grow to two feet or more in length.
yah the black P do get a lot bigger. but i think everyone agrees here that with RPB's diet and size they definitely need more than a 55. if you want a happy healthy, and active fish provide 'em a bigger tank. and telll your expert to go join MFK will set him straight.
here's memo (my RPB) 125 gal
indoor pond / belong's to a fellow member ... this is what you need for the pacu's and many other large fish , that pleco will grow large as well too depending on the specie .. good luck and up grade please , the health risk's are to great to not dew so ex: ammonia will most sertinaly spike if not already!!