Just fried donuts in canola oil and it smelled like I was frying fish. I've read this happens sometimes to canola at high heat. Anyone know w

Here's some more reading on this matter -- a paper from The Journal of American Oil Chemists' Society: http://www.springerlink.com/content/nx8152t42151662q/

When you heat oil, you release aldehydes, a particular kind of organic compound. Many aldehydes have fragrances, which can range from fishy to citrusy to smelling exactly like a banana! You can see a list of aldehydes present in oils and their smells here:

http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4281709/84607_09.pdf

Oils breakdown and develop smells particularly when exposed to direct sunlight, or when they age and become rancid.