[xAnnaVictoriax]

About a month ago I've adopted 2 new rats after a year without.
Oliver is doing fantastic, and he's about 3 months old. Argotron is about 5 months old, and we got him a week after the first rat.
He was way more timid than Oli, but he seemed to be warming up to us fine.

Their introductions went OK at first, until about a week of switching scents/bathtub meetings. Argo suddenly started getting REALLY aggressive. I had been letting them fight things out, and Oli finally stopped being so dominant and submitted to Argo. This lasted 10 mins, but then Argo just started viciously attacking him out of nowhere..they were eating together and everything, I don't know what triggered it. I separated them as Oli had huge bite marks on his sides. Then about 3 days later, Argo started being aggressive towards my fiance, stopped taking food from us, and just seems super skittish (even more so than usual).

Right now my fiance can't even let Argo sniff him, because he bites really hard and doesn't let go, you have to pry him off. I have trouble keeping him in the cage,because everytime I open it to put food or new toys in, he runs out and I have to grab him with a towel to get him back in..
I don't know what to do...
We have them in the same cage but on different levels (3 level cage, Argo on bottom where he can hide easier and feel more comfortable..piece of slate on the bottom of the top level so he can't pick at Oli's feet and tail like he did the first time.) He also chews the bars relentlessly, even though he has tons of chew toys.

Any tips? We are going to try getting him neutered, though the vet here charges $200+ I just feel so bad for him..
Argotron
Oliver

 

[Rat Daddy]

There are multiple reasons for this kind of problem... A brain tumor or other health issue can come on suddenly and really mess up a rats behavior. Then there is alpha confusion, which is less likely to be this sudden or violent but still an option.

A vet needs to investigate for health causes and alpha confusion can be addressed with extreme immersion or neutering or both...

I'm only going by what you've written, not seeing your rat for myself, but if it is as severe as you make it out, I'd have the vet check him out before you try anything else. Neither neutering or resocialization is likely to help a sick rat. Brain tumors are rare, but they do happen and they look a lot like what you described, so don't panic... but rather to be concerned until it's investigated.

Best luck.