Do you think this is a Spraying cat or not?

I came home yesterday and i keep my cat in the bathroom because he is a kitten and is feisty and i dont want him to destroy my things and when i came home and let him out the whole bathroom smelled terrible....almost fishy and we have been keeping him in there for a few weeks now and it had never stunk. Do you think it is him spraying or could it be sewer gas coming from the toilet.