seperating two aggressive rats

Question
hi i've just had to take one of my rats(i have 19)to the vets with a nasty wound caused by his only cage mate and she advised me to separate them. this will mean that i will have two rats housed on their own (as i've tried introducing new rats to them in the past). how can i tell if they are unhappy on their own?

Answer
 Though it is true that most rats do much better in pairs there are those (usually males) that simply prefer to live alone.  If you've tried and failed to introduce new rats to them, they are fighting constantly with each other and injuring each other then that is their way of telling you they'd rather be alone.  Rats like this do perfectly fine on their own, but just make sure they get lots of handling from you or at the very least some free play time outside of their cage.  I hope this helps, good luck with your rats!