I used to be quite a fish tank man.
The first time I got oscars I didn't realize they were so aggressive. I put them in a tank with about 20 other fish. Fish kept turning up dead and I kept flushing suspicious looking other fish until about half my fish were dead either at the teeth of the little oscars or in the maw of my wc.
Finally I realized the oscars were guilty and traded them back to the fish store for something that ate plants.
Years later I bought just two and raised them til they were as big as my hand or so. One was bigger than the other and soon was biting it all the time. I eventually had to put the aggressive one in solitary.
When we moved to a different home in the cold of winter the oscars stopped eating and soon died.
Now I have children, grand children and a largish bunny. My Mrs. has a smallish finch type bird.....and a half dozen or so very very hardy plants.
Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.

[SIGPIC]
..I also have a 427 Cobra replica with an aluminum chassis.