I have seen many cases of a single Jar housed with other fish here in Australia succesfully but I have never seen success with two or more Jars housed together.When it comes to conspecifics,they are definatly solitary.Even wild caught specimens often show signs of fresh battle scars.If you have plans on trying to keep a Jar with any other fish species,I would get rid of the dominant ones first IMO and keep the least aggresive.
If you are happy with a single specimen tank,choose the largest most dominant one.
