Research shows that 1g/day of omega-3 fatty acids can help slow and prevent OA.
You can get your daily dose from a 3oz serving of salmon, sardines, or mackerel, or from omega-3 supplements.
Supplements should contain both EPA and DHA, two types of omega-3 fatty acids. (The third common type of omega-3, ALA, is found in plants, and has not been shown to be effective for osteoarthritis.)
Here are several well-reviewed options on Amazon: