If I found mold on my fishsticks what should I do? can i sue for that?

Yes you can sue, but there a lot of questions you don't answer which may be relevant to who to sue and for what.  Did you eat the fishsticks?  Did anyone get sick from them?  How long ago did this occur? Did you buy the fishsticks in a grocery, order them at a restaurant, eat them at a friend's house? Do you know what brand of fishsticks they were?  Had you stored the fishsticks in your refrigerator for a long period of time?  Did you buy them but then not refrigerate them for some time?  Was there a power outage while you were storing the fishsticks?  The bottom line is that if no one was injured by eating the fishsticks, the most you are likely to recover is the cost of the fishsticks.  If you complain to the store or restaurant where you bought them, they are likely to refund your money voluntarily.  The manufacturer, too, might be willing to compensate you.  However, if nobody got sick, it is probably not worth the expense or hassle of a lawsuit.