I have 2 tiger barbs ( normal striped kind ), a red tailed shark, a female betta, and a black molly all in the smae tank, a 10 gallon at that, never had any problems, the betta however loves the mollie, and the barbs still keep trying to takeover the cave the shark stays in, but he won't let it happen, Barbs however do nip really badly, I had a tank a few years ago that was a 29 gallon and I had 3 green tiger barbs, some kind of spotted catfish thing, a huge 16 " pleco, 2 angels, a fancy tailed goldfish and a huge goldfish that grew way to big and broke his back agianst the tank wall. the tank was truely overloaded and it couldn't handle that many fish it was so nasty after a week, but anywas my barbs nipped everything the could until the pleco rammed on agiasnt the wall and killed it and the others died of old age, I thought plecos were peaceful, but apperently he had enough lol