Pacus are shoaling fish and really do like the company of their own kind. Keeping 1pacu is making the fish pretty miserable. I had 4 pacus a while back in out 10ton pond together with some large kois in Malaysia. They grew to about 50cm (20inch) and well, at the end of the day, it ended up on the dinner table. Pacus are farmed for table fish in many Asian countries (china for instance) because of their size and their growth rate.

kev