Is cloudy-looking used peanut oil safe?
May depend on the temp. of your fridge, but when I have stored a brand new (i.e. unused) bottle of peanut oil in my fridge, it has gotten cloudy and thick, especially when the level in the bottle goes a little below full. When I wanted to use it and took the bottle out of the fridge, it "thawed out" as soon as it got warm, and looked &amp; acted just like when I bought it. 

Canola oil does not behave this way for me. So this might just be a property of peanut oil when it gets cold. Does your left over oil thaw out &amp; look clear when you let it get to room temp.? 

On the other hand if you have used it to cook fish, I imagine it will still have at least a slight fishy taste even if it is strained out perfectly. Maybe best not to use it for fine delicately flavored dessert items anyway.