Goliath and Vittatus and all other species of Tigerfish can be kept togther depending on the size of your tank, i have had mine for about 2 years now and they are all roughly 9 to 10 inches long and all get on fine, i have two wolf fish, and 6 african tigerfish, 2 vittatus 1 Goliath 1 Brevis and the other two i believe to be other species with the more dolphin shaped snout, when they reach closer to the 14 inch mark things might start to change i terms of how well they get on!!! hwoever as everyone who kees these will know they do take ages to grow so im not worried at the moment.