My Black Moor Fish is ill, can anyone help?

Ok I bought a small sized black moor from the pet store about a week ago he seemed to be settling into my tank with my other fish quite well. Suddenly tonight i noticed he is having great trouble swimming and he struggles to get to the bottom of the tank and keeps floating up to the top, I turned my filter off to make the current of the water not so strong for him to try and swim against.

There are no other symptoms (like white spotting/discolouing) just the fact that he is swimming at the top and struggling. He is always on one side as well, I keep looking, it looks like he is dead and then when I go near the tank he will start swimming again. I'm really worried. I don't know whether to do a water change or how to treat this. It looks like it might be shimmying disease other wise known as the shimmies, but I don't know if thats a tropical fish disease only.

Could you tell me what caused this, and how to treat it …. and is it infectious?
I dont have a spare tank to quarantine him I looked up swin bladder disease and it looks like thats whats wrong, can I treat him in the same tank with the rest of my fish … I've done this for ich etc before … What do u think?