I'd avoid Denison barbs - they're very active and perhaps too big for your tank. Also, they need cool (15-20ºC), well oxygenated and fast flowing water while the Shark needs 23ºC minimum.
Are you sure you really want a Rainbow Shark? Here's a few comments:
Compatibility: Do not keep with members of its own kind or any other kind of 'shark' unless there is plenty of space for both fish to establish territory and so they aren't in constant sight of each other. This fish can also be somewhat aggressive to other fish, especially other fish that live in the bottom strata. May also nip fins, but doesn't make it a habit like a tiger barb.
Decoration: This fish loves caves. Provide at least 2 caves, each on opposite sides of the tank. They will sleep in their cave. A cave of wood or rocks will make the fish feel secure. If shelter is not provided they'll take to any tight fitting secure place, including behind the heater, so provide a few caves to make them happy. Planted tanks also make this fish feel more secure, so a few plants are a plus ***CAUTION: will eat some plants, hungry or not*** Make sure the plants have relatively thick leaves, anubias or Java fern works well. The more secure the fish feels, the less aggression its likely to show. Badman's Tropical Fish
The Rainbow Shark is a freshwater cyprinid that comes from Thailand and may not be a good choice for a community tank. The Rainbow Shark likes to stake out their own territory in the tank. This territory can be in the form of small caves, rocks and even plants. They will become aggressive with smaller fish that invade this territory. Only keep one Rainbow Shark in your tank because they will not tolerate another Rainbow or Red Tail Sharks in the same tank. They may exist together for awhile, but one will end up chasing the other relentlessly until the other succumbs....... You will need a good tight fitting hood with no escape points because the Rainbow Shark has been known to jump out of the tank.......This fish can become aggressive with other, smaller fish in your tank that invade its territory.......Because of their temperament it is a good idea to house them with similar sized fish. Fishlore
The trouble with mixing barbs in with the Shark is that most barbs like to nose around at the bottom of the tank looking for food... and this is Shark territory!!