Packaged fish in lots of liquid - is it safe
Fish is tricky because the smell does not come from bacteria but from degrading enzymes. Cod tends to smell fairly early while being perfectly good to eat.

More generally for food to spoil you need water, warmth, a nutrient and oxygen (in most situations),so in the case of your fish it is likely to be good to eat, being vacuum packed and chilled.

The water in the pack can come from thawing or from 'weak flesh' (eg farmed fish). When this happens to me, I pat it dry with a paper towel and then salt it lightly on all sides as this will firm up the flesh after 10 minutes or so.

Obviously nothing replaces buying a whole fish you've looked at 'in the eyes' and butcher it yourself but we all have to deal with packed fish every now and then...