goes on a fish by fish basis, jars are known to be killers. but in some cases not.
I have a theory that I am testing, this came up from another aro keeper. He keep a small jar 6in, with a bunch of dats(3-14in). The jar eventually grew to 24in, he said that the jar has not eaten or beaten any of the fish in his tank. Our theory is that when the jar was young, the larger fish intimidated the jar. That in turn made him a mellow fish. The jar is still in the same 210 with about 12 dats(6-15in).
I also have a 210 with a 10in jar that I have had since 5in, that is keep with larger fish that don't take shiet from anyone. 11in longnose, 13in tropical gar and 3 10in tin foil barbs. Currently I have seen no fights or damaged to any fish. Jar competes for food very well, and swims together with the TFB. I am hoping jar will grow to 20in plus and still be mellow as it is now. it would be an awesome fish.