Short answer...no, these cannot be together. Primary reason is that both discharge electric fields.
Knifefish possess a weakly discharging neurogenic electric organ and ampullary electro receptors that are distributed from head to tail. This is used as a "radar" to detect their surroundings and to locate prey. The body is thus inflexible in order to function as a receptor of electronic signals returning to the fish.
Mormyrids (Elephant nose, etc) produce a weak electric field using specially-adapted muscle tissue located towards the tail. It also possesses electroreceptors which allow the fish to receive electrical signals. With these, the fish can sense the tiniest of movements as the field around it is disturbed, and navigate in total darkness, useful skills for a poorly-sighted fish when hunting prey or avoiding predators in the gloom.
