I very much doubt he suddenly became cafe aggressive, tbh that breeder is a moron. I've seen her site and completely cringed. I know of her practices and knowledge of rats overall.
So tell us exactly what he was like before he bit, was he gentle, confident, friendly, easy to handle in and out of cage? Did you get him as a baby and was he socialized or nervous with humans?
Then go back to him biting you recently. Did you have your hand in the cage doing something (putting in food, etc)? Did he dash out and chomp then run back? Or did he bite down and his fur was up and once you got him off you his fur was raised, possibly chattering his teeth?
I got Batman when he was a baby. From the start he was a bit less outgoing than the other two (Siamese) rats, who are about the same age as Batman but from a different breeder. I had no trouble handling him and taught him to ride on my shoulder. He seemed to be socialized, never showed a sign of fear or aggression. I would take my rats out to play for a few hours each day. They were in a refurbished large bird cage when I first got them. From the beginning they'd all come to the side of the cage when I entered the room, and I'd give them small treats like pumpkin seeds or shreds of coconut. They always took the treats with no attempt to bite me. Once they got bigger I moved them to a wire dog crate cage. Neither cage move caused any behaviour changes.
Then in early August I became very ill. I was only able to do the food/water change each day. I was too ill to take them out. That lasted about a week. I had bought cc cubes to build them a bigger cage, as they'd grown out of the dog crate. I built the new cage and moved them to it in the third week of August. They seemed fine at first.
Then I noticed that when the other two came to the side of the cage for treats, Batman would stay back, but watch me intently. He'd only take treats that were on the bottom of the cage. I started watching him carefully, wondering if he could be sick. I noticed he was spending most of his time in a cardboard tube that only he could fit inside. Before, he always slept in a heap with the other two. I also noticed him gazing straight upwards a lot. He would sit and just stare at the ceiling. He started coming near the cage bars when I was feeding treats, but still wouldn't take them, in fact he'd back off and shake his head. But he'd stare at my hands and follow them with his nose.
Finally one morning I was unhooking their water bottle from the cage, with my hands on the outside, and Batman leapt at my hand and bit it, hard, through the bars. I yanked it back on reflex. My finger started spouting blood immediately, there was blood all over the place. I was so shocked that at first I didn't know what had hurt my hand. At first I thought it was a fluke, that I must have done something to provoke him without knowing it and he'd be fine the next time.
Next day the two Siamese brothers came to the cage bars as usual, looking for treats. Batman came to the bars as well, pushing his nose through like the others. But when I offered treats, he backed off about an inch but fixated on my fingers. I decided to leave him be and just gave seeds to the other two. But, while I was giving a seed, Batman darted at the bars, pushing his face out and tried to bite my hand again. I don't remember if his hair was raised that time, it happened so fast.
Since then he's bitten me twice more, the latest bite was yesterday. He managed to dash in and bite me while I was picking up something I dropped just beside their cage. I wasn't paying attention. Then yesterday he lunged at me while I had my hand in the cage putting their food dish in, and caught me before I could get the hand out again. He bites HARD, I can feel the muscles in his jaw quivering as if he's biting as hard as I can. The bites are surrounded with bruises from the bite force. He has not latched on to my hand, or maybe I yanked it back before he could get a good grip. I've never seen or heard him chatter his teeth.
So I'm in a bit of a quandary now. I'm not against neutering him if it will help, however, I won't be able to afford it for a few weeks. I'm concerned that his sudden aggression could be caused by the Silvermane gene, in which case neutering won't make a difference. If it is the Silvermane gene, there's a very good chance he will eventually attack and/or kill his cage mates. I have a spare cage and could separate them, but I'd feel badly for Batman being alone, and afraid that it might make his aggression worse. Speaking of afraid, right now I'm pretty reluctant to try handling him, even with gloves on. I've lost fingernails to parrots biting through heavy gloves.
