The problem is your tank size. I have a managuensis, JD, and venny pike that were housed in a 55 gallon. The jag and JD would jaw lock and the jag would get his face all tore up (although the jag is a relentless little bugger that always started it).
The ONLY way to keep a jag and JD together is to have at least a 125 gallon tank.
So, the question is; what size is your tank?