Yeah, I noticed a huge difference fairly quickly actually. The kind I buy is by Brunswick (Canadian Co.) 84g can in spring water. I didn't feel that I needed to buy one in an oil since the fish itself has tons. Man are they ever stinky!! So, JLers recommended just dumping the whole can on his food at one meal, but D's stomach can be sensitive so I opted to just give him 2 single sardines from the can once a day (usually 3 days). I start Sundays & don't open another can til the following Sunday.
Just be careful to read the label, some have extra spices, etc. Just get the plain ones, make sure they have the skin & bones for the added good stuff.