The small group of tropical freshwater fish known by their common name of 'sharks' have very little relation to the large predators of the oceans, but they are still an interesting group of aquarium fish
The 'shark' name comes not from any relation to marine sharks but from the fishes well-defined fins, particularly the shark-like dorsal fin, and the sleek body shape. The freshwater sharks however, can be quite a handful in their own right, and should always be chosen with care.
Freshwater sharks have plenty of character and presence and in the right environment, a freshwater shark can be a great addition to the home aquarium. In the wrong environment however, some of the freshwater sharks can become your worst nightmare.
Ruby's, red-tails, and rainbowsPerhaps the best recognised of the sharks is the Red-Tailed Black Shark (RTBS) Epalzeorhynchos bicolor The jet-black colour of the solidly shaped body perfectly shows off the fish's well-defined 'shark-like' finnage and bright red tail, and it is this appearance that has made the fish so popular.
Although often sold as a community fish, many fish keepers have since learnt better. If it is able to, a rogue RTBS will dominate an entire tank, terrorising and harassing the other fish, especially in smaller aquaria.
A RTBS however, will only pick on the easy targets - mix a red tail with fish unlikely to feel threatened or run away, and the red tail will soon stop trying, or at least cause little more than an occasional squabble.
For this fish, robust tank mates like large barbs, peaceful cichlids, and rainbowfish are the ideal choices. Typical smaller 'community' fish, timid species, or slow moving fish will not fare well against a RTBS.
A good alternative to the RTBS is the Ruby Shark Epalzeorhynchos erythrurus, a similar looking fish with a slightly lighter and more slender body, and red colouration on all the fins. Although still a little territorial, the Ruby Shark is much more sociable and with the exception of very delicate fish, can be kept in community aquariums.
The Ruby Shark is often confused with the Rainbow Shark Epalzeorhynchos frenatus, which sports a lighter grey body and slightly different fin shape. The differences in behaviour and size between these two fish however, are not significant enough to cause concern.