I guess this is a question for Dr. Doug. My wife takes a daily fish oil supplement, and several years ago it was suggested that she share them with our pups, so for the past couple years she has give...
I'm not Dr Doug, and would defer to his knowledge.... but here's a chart to give you a rough idea meanwhile. And it looks like the dosage they recommend is for osteoarthritis. If that is not an issue, and you are just giving it for skin and coat, the dosage may be less.