There would be a good chance that the Fahaka kills the Jaguar, of course, if the Jaguar is big enough to swallow the puffer, you'll have two dead fish on your hands. I guess it might work if there were enough fish in the tank that the Fahaka's aggression was dispersed between multiple targets, but you'd probably have a tank full of chewed up fish... Then again, fish do have individual personalities to a certain extent, perhaps there is a mellow fahaka out there, I haven't seen it, but it may exist...