Any fish that can hold its own so the more aggressive cichlids like green terrors , texas cichlids , mabye jaguar could work my mayan cichlids was pretty aggressive and most others are to some are mild mannered but these mayans are pretty rare most are at least some what aggressive but a great cichlid can have some pretty nice colors and they eat a TON
Still not sure why people recommend mixing aggressive species like uros & jags with paper tiger species like GTs.
As for what will work with a young uro, probably lots of things, but they will have to be decently aggressive to keep up. Which leads to problems when all of those aggressive fish hit adulthood. A full grown 14-15" jag probably won't play nice with anything in a 125. Mixing the large aggressive species will have a better chance at working in something larger. Guess you can try it and see what happens since every fish will have it's own personality.
I have Mayans with GTs, JDs, a Firemouth, Texas Cichlids and FHs. There are no problems as of now, but they are all under 5". WHEN the problems start, I will thin out the herd.
yeah the jag was men't as an example they wouldn't work the best as the can be very aggressive and get pretty big and GTs useually hold up pretty we'll but could get beat up
Male mayans get around 12'' females a little smaller so it wouldn't out grow a 125
I would go for around 5 large cichlids in a 125 if you have good filtration and mabye some dithers they would help with aggression