^ this

First idnetify what kind of passive fish you have...
calls too many raises and folds to too many cbets... widen both your value and bluffing range.
calls too many raises and stations down anything with showdown value... widen your value range and narrow your bluffing range.

And yes, if a passive fish shows aggression, he has either adjusted or he has a big hand, usually the latter. Trim your continuing range accordingly.