Has anyone else had a Gnathonemus petersii & pimelodus pictus sharing community tank and fighting?

just have a question regarding the social behaviour of a couple of the fish in my partners 4ft community freshwater tank. We have today purchased a beautiful pimelodus pictus and introduced it to the tank. Please bear in mind this is our second pimelodus pictus as our first one went missing and is presumed dead. We have a gnathonemus petersii in the tank and while it is generally peaceful towards others in the tank (rainbow fish, plattys, bristlenose's etc etc) it has taken a instant dislike to the pictus. It almost seems as though it seeks it out in the tank only to har and chase it. We were advised by the salesperson that the two breeds should interact fine. We do think that the elephant fish had something to do with pictus #1 and its dissapearance. Pictus #2 seems rather stressed as one would expect but does not fight back or retaliate. Any help or advice would be appreciated as we would love to keep both fish but do not know what to do re: behaviour towards eachother