Well for starters, when the Oscar is big enough, he will probably eat the Tiger barbs and tetras so I shouldn't put any small fish in with Oscars. I would probably put a few silver dollars in if it was my tank. You could go for three or four pictus catfish but make sure they are relatively big when you get them. Remember that catfish are nocturnal and will be active at night. For this reason, give the Oscar somewhere to retreat to sleep so he doesn't get disturbed too much. That's just a couple of suggestions, I'm sure other people will give you a few more
