Aros borderline imo… there pretty tough and hardy once they hit 18-20”. Will pose no problem together when the oscars are 10-12” and the aro is 28”+… cichlids can be terds tho i agree… but… ur tank should be more than large enough to not worry also. Can always try and watch out for nipped/torn fins then pull the oscars if needed.Now the dilemma..... All along I had full intentions of keeping my Oscars and arowana both in this tank. With that said I have heard stories of Oscars killing much larger arowana so now I'm kind of nervous about putting them together because I love my arowana!!! This tank was built for the him pretty much. My arowana is now roughly 13 to 14 inches and the three Oscar that I plan to put with him now are roughly 5 inches. With the large footprint of the tank I would like to think it would be fine but I have never housed these two species together so was just looking for a little advice from someone with more experience than I lol.