There are a lot of rules and people saying you cant keep them with this and that, and most of the time they are right.
However every fish is different and a lot of it is down to the individual fish, and setup, its never "black and white" there is a lot of grey area.
There are some fish that are a lot more risky than others like lungfish and puffer fish like MBU's are a very risky mix and i just wouldnt.
But things like peacock bass and gars while still advised against are a lot less risky to try and keep with rays and most of the time these make fine ray companions.
Just use common sense to figure out what is totaly unsuitable but some things can be tried as long as you have the ability to remove the offending fish, and trying stuff, while quite a risk is the only real way to find out.
However every fish is different and a lot of it is down to the individual fish, and setup, its never "black and white" there is a lot of grey area.
There are some fish that are a lot more risky than others like lungfish and puffer fish like MBU's are a very risky mix and i just wouldnt.
But things like peacock bass and gars while still advised against are a lot less risky to try and keep with rays and most of the time these make fine ray companions.
Just use common sense to figure out what is totaly unsuitable but some things can be tried as long as you have the ability to remove the offending fish, and trying stuff, while quite a risk is the only real way to find out.