I have found that my two Pacu's are extremely docile to my other fish - blue acaras, port acara's, pleco's, pictus cat, and synodontis - but they are very aggressive towards each other, to the point of almost completely ripping each others dorsal fins off. They love fruit and are very fast growing fish.
I had 2 pacus given to me. They were already large when I got them, but now the big guy is about 50 cm long, the smaller one about 40 cm. They are extremely skittish, just yesterday I came home to find the big one on the floor! He had jumped up, knocked the lid off my tank, the light fixture into the tank, and thrown himself out. Luckily we got him back in water on time. He is beaten up pretty badly, with torn fins and scrapes on his head. I now keep weights on top of the tank. I also have been told these fish are supposed to be vegetarians...mine ate two oscars, two plecostomus, and three smaller catfish. They do love pears though, but won't eat the skin.
I have had a red belly pacu for about a year. He lives in 280 liter tank. He eats shrimp pellets and bloodworms. His nose is messed up because he used to freak out and do nose dives into the gravel. He doesn't do this anymore and is very calm. He has only eaten fish that have died, that I haven't taken out because I didn't know that it had died. He isn't aggressive and is a wuss. I enjoy him and like the way he looks. He lets me rub him with my vacuum. He usually stays on the side of the tank that has more open space.
I had a red belly pacu in a tank for about three years. He was with two oscars, a convict, a jack dempsey, a pleco and some type of large goby. Well the pacu ended up getting pretty big, he would splash water out of the tank. He was a little bigger than a dinner plate. When he more than outgrew the tank, and out of fear of him breaking the tank, I had to get rid of him so I gave him to a public aquarium where he was put in a tank with may other pacus of the same size. I named him Tim after some guy at my work who looks just like just like him. Usually I gave him strawberries and and a bunch of other stuff, but I found that he and the oscars liked insects a lot.
I have had two Red Bellied Pacu's for about eight months and I just love to watch them in my tank. My Pacu's love to eat any and everything I give them. They especially like it when I feed them live feeder shrimp once a month. They have grown so fast in my 400 L tank that I am getting a larger tank so they will be more comfortable.
We purchased a Red Belly Pacu about 2 years ago. He is now about 45 cm long. He is huge. He eats algae disk and can fit about 20-30 in his mouth. We had him in a 200 liter with 2 Oscars who ate feeder fish. He apparently did not like the idea of them eating other fish, so he slowly killed them off. Now we have him and 12 feeder goldfish (who are now huge), 2 pink kissing gouramis and 2 pleco's in a 380 liter tank. We are going to get rid of the goldfish (a friend of ours has a huge pond). He does seem happy in the tank with them all.