Can a pacu live with a turtle?

It all depends on the size of the turtle and the pacu. If the pacu is at least the same size as the turtle then it is okay for them to be tank mates. The worst that would happen is that the turtle would be able to nip on the fins of the pacu which will eventually grow back. aquatic turtles produce a lot of waste so make sure that your filter is rated for twice the gallons that your tank holds. The species of turtle and the age of the turtle will make a difference as well, for example red eared sliders are more herbivorous when they get older, past 5yrs, while snapping turtles will have a higher chance of injuring/killing your pacu. It is very important that both the aquatic turtle and the pacu are housed in a large tank/pond because they both get big. This will decrease the chances of them encountering each other.

Experienced aquarists never mix fish with Amphibians or Reptiles because they know they are heading for failure. It is recommended that many Reptiles (depending upon species) be kept in a set up where they can actually get out of the water and dry out a bit and sunbake too sometimes. As the other person above wisely says, the Turtle could also damage the fish by biting chunks out of it.