The Red Tail Shark is very territorial and can be overly aggressive, especially to their species and fish of a similar appearance, such as the Rainbow Shark, Sliver Flying Fox and some algae eating loaches.
It is recommended to house these fish with other semi-aggressive fish or ensure the aquarium is large enough for the other fish to escape harassment. In keeping with other shark type species ensure there is a group, so the aggression is more distributed instead of focused on a single fish.