When you are suspicious about something, probably when it seems dishonest. It is an informal why of saying, when you are doubtful about something. For example,"Elan getting into a business agreement with Susan,sounds fishy" "A rapid increase in Tom's bank balance smell fishy to me" Hope it helps:))

yea....something suspicious, there is something wrong around...

I guess you know that "fishy" in this context means suspicious. It's as if you have smelt something that was "not quite right".

You can say it when your suspicious of something, if something doesn't seem right, or if you smell fish!