The Best Tankmates For A Red Tail Shark
Red Tail Sharks do best in large aquariums with fast moving (but not overly aggressive fish). It is often recommended that a Red Tail Shark can work well in a cichlid tank, but experience and a bunch of ripped fins have taught me that this is not the case – at least not if the cichlids are the flashy, brightly colored African variety. South American cichlids seem to be more laid back, or at least, less likely to view the Red Tailed Shark as something to be devoured.
When considering tankmates, one also needs to consider tanks. The twenty gallon recommended minimum isn't a minumim because this fish gets particularly large (15 centimeters is about the max) but because smaller confines make it too aggressively territorial. My red tail, forced to share a ten gallon tank with a Jewel cichlid (because they had both been victims of terrible bullying in the main tank) promptly went after the Jewel with vicious attacks that would make its namesake proud.
Although Red Tail Sharks feed largely on vegetable type matter and have mouth parts more suited to rasping than tearing off chunks, those mouth parts can do plenty of damage when applied to the scales of another fish. At the end of the day it became necessary to separate the Jewel and the Red Tail Shark. The tank was simply too small for the both of them. Let this be a cautionary tale if you are considering introducing a Red Tail Shark into a tank smaller than 20 gallons.
Aggression is a common problem in fish keeping, more common than you might imagine. In my experience, keeping fish is 50% chemistry, 50% aggression management. If you get the water conditions right, that's only half the battle won, you also need to ensure that your tank is stocked with fish that do well together.
The desire to keep 'community tanks' with fish of various species originating from different areas in the world causes a great deal of trouble, though it can work on occasion. For instance, I keep a Jack Dempsey (a South American cichlid) with several Dog Tooth Afras and other related African Cichlids from Lake Malawi. The Jack Dempsey does fine because he is by far the biggest thing in the tank and more than able to defend himself, but the Jewel cichlid (also a South American cichlid) fell prey to bullying very quickly and had to be removed, as did the Red Tail Shark (which originates in Thailand.)
Prior to the introduction of African Cichlids, the Red Tail Shark, Jewel Cichlid and Jack Dempsey had all gotten on very well. So, as you can see, I was a fool to upset the balance with the Africans. You live and you learn. Either keep your Red Tail Shark in a large aquarium with larger (preferably South American) cichlids, or keep them alone.