I had my P. Annectens in with fish for almost two years,and apart from one chomp "he" was good...until about six months ago, when he started chewing on everything and now has a tank on his own...The only lungs I keep with other fish are the SAL. I tried keeping my Fly River turtle (6") in with my big SAL (36"), which lasted about a day until the FRT began biting it's tail...
And what did I learn? Lungfish and turtles do not mix...