Advice needed. Feral/stray

Hi, about 3 weeks ago  i rescued  a cat that just showed up on my deck, trapped later that day. I live in a semi rural area , and  we think it may have been dumped. I have 5  indoor cats , 2 which were feral . I brought  him to the vet to have him neutered and tested, then  put him in a cat condo cage, which is now in my family room. Vet seemed to think  that he  had to have had human contact at some point. At first he was so shy and fearful he would cringe when  i reached in to touch him, but he allowed it and seemed to like it. The past few days he  started hissing and  attacking when i go in to pet him. One of my cats  is very easy going and actually goes in the cage with him, and he seems to like it , although he just  puts his head down and goes to sleep. The other cats  lay by his cage  and i want to let him have free roam of the house soon , but  I am wondering why he has suddenly become aggresive? Has anyone  had any  similiar experience, and could offer some advice, I really don't know what to do next . Thanks so much .

By the way the vet said he is between 12 and 18 months, so  not a kitten.

He may feel trapped by the other cats, even though they seem to getting along.  But five to one and he's in a cage, you know?

It might be better to give him more space - a room to himself, perhaps.  You can also lock the other five in a room and give him some time alone in the house.  If you do let him out of the cage, make sure you can get him again.  He may bolt and find a hiding spot.

The aggression may just be him feeling a little intimidated.  Do you have Feliway or something similar in the house.  This is a plug-in device that has cat pheromones.  It will help all of them all feel calm and help everyone adjust to the newbie.

Thank you for helping him!

Thank you , that makes sense . I did have him in his own room for the first 10 days , and I have a feliway diffuser , I will try to give him some more alone time . Appreciate the help .

You're very welcome.  And welcome to TCS!

I think the aggression is because now he dares.  He didnt dared earlier, he was trying to manage, to try and copy as he could, to survive.  Now he begin to understand there is no real danger for him any longer, he actually is fairly safe.  So now he dares to say no.

I think it is actually a big step forward, NOT a backlash.

(unless he has pains somewhere, but lets hope not).

Just to proceed!    Use your residents as  your ambassadeurs, cuddle them much where he sees you, not least, the one who is beginning to be his pal.

Good luck!

My experience with my indoor feral matches what Stefan says about your kitty feeling bolder.    Initially I had her in a bathroom and she'd scrunch down into a tiny ball in a corner here or there and I could approach her and pet her - she did not strike out though she was hardly purring.  She also never made a sound or tried to get out.  Once she was out in the rest of the house and integrated with my other cats, she did lash out a few times when I pushed petting and I had to wait for her to approach me (winding around my legs so I could reach down to pet her) which took quite a few months.   Have patience in time it'll work out.    Year later now and I can't shut her in a room without her scratching at the door or howling at me.....she feels she's got right now!