After salmon has been defrosted it is usually only good for around 2-3 days, so you will need to make sure that you throw it out if it has been in your refrigerator any longer than that. By eating spoiled salmon you can expose yourself to all kinds of bacteria that could potentially cause food poisoning which can lead to fairly serious symptoms.

If you do not plan on eating the salmon which you bring home from the supermarket right away, it is highly advisable that you freeze it so you will be able to keep it around for as long as you need it without having to worry about it going bad.