Our local Petco has a humongous pacu that must weigh at least ten pounds in an outdoor style freestanding glass pond. I understand that the pacu is a copycat to the pirhana, which I have seen at Seaworld in San Antonio, and the adult pirhana's were about four pounds. Is the pacu I am talking about a genetic freak or do they actually get this large? It seems that the disguise would be less effective if they are not the same size as the fish they imitate.

Scientific name …colossoma brachypomus (silver) or colossoma macropomum (red-bellied)

The pacu originate from the upper Amazon, and they can grow to be between 18 and 30 inches in length,

They are related to a piranha, but not a piranha per se. Those who own this breed of fish say that they are a friendly breed and intelligent. The only time they act like a piranha is when they are small, but this is merely a protective behavior until they reach a certain length then this behavior ends.

It also has been noted that while pacu are mostly a vegetarian, they will if given the opportunity, eat smaller fish in the tank. Some owners say that they get along well with other community fish, while others have reported missing fish.

Interesting, this one is at least 20 inches long and six inches thick I would estimate. It is a massive fish larger than any Oscar I have seen. In fact I thought at first glance that it was an Oscar, but on second glance it was clearly a pacu. It is in a tank with koi and a few Jack Dempseys. The JD's do not mess with him though!

Thanks piggins, for the good answer!

I had a giant pacu for 4 years, sadly he died durring Hurricane Andrews in south Florida.
This was no mere fish but was an actual pet and odd enough, a friend.
I had suffered from intestinal cancer and confined to home for a year in which time I got to know this pacu quite well. I named him pug because he was very timid at first and rammed his face into an aquarium rock, removing a big chunk of skin from his upper mouth. He didnt seem to suffer it much but I know it pained him.

Anyhow, I eventually could stick my hand into the water and rub him, he would even swim up to my hand and brush against it as if he wanted to be pet. He seems to have loved me quite a bit but didnt care for my wife much, making here sorta hate the poor guy.

When she got near the tank he would splash water hard enough to knock the top off the aquarium and scare the hell out of her (I thought it was funny, she didnt)

He wanted to eat anything I was eating and would do the same water splashing till he got it.
One day I was tossing m&ms unto the air and catching them in my mouth as he watched. Soon he began splashing the water and letting me know he wanted one.

I dropped it into the tank and it went to the bottom as he watched it sink. He began splashing water again.

This time I threw the m&m into the air and it went into the tank.
The guy darted after it and seemed to have swallowed it, then to my surprise he spit it out and caught it between his teet (he had teeth) and turned to look at me and shook his head as if showing me he can catch them too.

He was 24" long and from bottom to dorsal was 18 1/4 " tall. Very large indeed.
He would eat spagetti noodles but only if I held it up while he gulped it down.

I had named him PUG because the damage he did to his nose PUG NOSE.

They are very smart and given proper attention can easily become a very amusing pet.

I just wanted to share this story with other pacu owners.