I wasn't very scientific with the fish oil. The husky was large, over 75 lbs., and I gave her 2 1000mg capsules a day (the dosage recommendation for a human). She didn't like the capsules, so I'd have to open them and squeeze it on her food.
Our springer/pointer likes them so much, I just give her the capsules. I let her sniff the first set, and she got very excited and snatched them out of my hand. She's a smaller dog, and I've been giving her 2 of the 1000mg capsules, though not consistently. The more consistent I am, the better her coat looks.