Fish oil is good for your joints. The good fats found in fish such as salmon and mahi-mahi, and in walnuts, canola oil, flaxseeds, avocados, and DHA supplements as well as the omega-9s and/or polyphenols in olive oil, are good for just about every part of your body. Omega 3s are believed to help provide lubrication that the joints need to function at an effective level while decreasing inflammation. By keeping the joints lubed, you experience less friction, less grinding, and less pain as you age. Another bonus: Fish oil (DHA, or docosahexanoicacid, for you chemistry fans) and fish protein have been shown to regenerate the membrane of the meniscus, which can help if you suffer a painful tear, or have chronic meniscus discomfort.
If you don't like fish, try fish oil capsules -- about 2 grams a day is the equivalent of thirteen ounces of fish a week (and because it is usually metabolically distilled, it comes without the contaminants some fish have). Even better, if you just want the active oil with even less chance of impurities, you can take smaller capsules of DHA, as all you need is 400 milligrams for women and 600 milligrams for men. You can get these purified, from algae (which is a vegetarian or plant source). That's where the fish get these oils from. If you're taking fat soluble vitamins like vitamin D3 and want to absorb them, you need some fat in your stomach and intestines first -- so taking DHA before the rest of your vitamins helps absorb the fat-soluble ones.