The 'blue gourami' is what? A three-spot? (trichogaster trichopterus)
What's the 'orange'?
Are they the same species?
When you say they 'attack each other', do you mean they actualy attack each other or one chases the other around? Do you know what sex they are? If they are attacking each other, I'd expect them to be male and I don't find this behaviour surprising at all since three-spots, and other gouramies too - but usualy to a lesser extent, are territorial and the males will sometimes fight to the death. I have tried keeping 2 male three-spots in a 20 gallon - I know am a firm believer that you can only keep male three-spots together if you have lots of females and a large enough tank to accomodate them all (it also helps if you combine lots of color morphs for some reason) and lots of plants.
How big is your 'pretty tank' and how many of each species you listed do you have in there? I suspect they attach the gourami because there is limmited space and he is intruding in their home. Also, it's no surprise the barbs attack him - those are very nippy fish and gouramies have nice long, tempting fins.
