I have 1 Channel(18"), 2 tsn(18" and 16"), 1 jau(18"), 1 rtc(16.5"), 1 pleco(13"), 2 oscars(14", and 12"), and 1 jaguar cichlid(14.5"), and 1 ckf(16") all in my 1100 gal pond. The way I see it is that the oscars are way too tall to fit even sideways in my tsn or any other fish in that tanks mouth. There is no aggression between any of the fish except the jau likes to pic on the channel, and rtc. The TSNs never bother anyone, they are the most mellow fish I have. They just wait on their shrimp to be handfed to them, and the rest of the time they lay in their hiding spots. The oscars swim around looking for pellets that I throw in for them. Here's the thing my biggest tsn is 18" which is 4" longer than my biggest oscar, but yet his head is like maybe, and I say maybe
2.5-3" wide. The oscar is probably 5-6" tall and 2" thick. There's no way in hell they are getting eaten for a long time to come. Their major threat would be the rtc, and the jau. The rtc is only 16" but his head is already 3.5-4" wide. In another 6 months or so I would say that my oscars days are numbered, except I hope to have my bigger pond up and running by then, and my oscars can go in the 350 gal pond. I started with already large oscars though. They were already like 8" each when I got the first TSN at 3". Hope this helps put some perspective on things. Again aggression is not the problem unless in a small tank, but in the future like 6 months to a year from now the oscars might be chow, but they are not too expensive, plus they are not catfish lol. I can always find people around here who say their oscars are too big for their 10-30 gals, and get them for free, but no one in montana save for me has RTC.