You know, I really don't know anything about Oscars or other aggressive cichlids. I do have a Blood Parrot and he is fairly aggressive towards the baby Blood Parrot (BP) that I have but other than those I don't have any experience!!
All I can say is that I would think that since it's a small Oscar ?? that it should be okay for a few days or so in your 29 gallon. Who knows.....maybe it won't be as aggressive as some??
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Do you have enough territorial space available for the Oscar to try and make a home for himself in your 29.....?? Maybe get a few more plastic plants and stick him in and see what happens?? You would only need to keep the Oscar in the 29 for a week or so is what I'm pressuming since your filters are established already, right??
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Your tank should be over the hump in about a week!!
You could always do what I've had to do with my Angels.....someone - who was that again
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- adviced me to make a wall/divider out of plastic plants so the Angels could have their "area" because they were becoming aggressive towards the other fish but not themselves. I believe they are praciticing the mating process
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. Anyhow, your Silvers, if not too big, will probably hang out on the one side of the tank and the smaller guys will probably go back and forth. Doing something like this may make the Oscar feel that he has his "own" space
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. Maybe start with the wall in the middle and see which side the Oscar takes liking to, if either, and then squeeze him a little and give him maybe only 1/3 of the tank.
Again, I have really no idea, but that's probably what I would do if I had no choice in the matter.
Hopefully someone more experienced will reply before you have to take action
Good Luck!!
Silver
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