I’ve heard this recommend. Fish oil has omega 3 fatty acids. These are really good for your brain and your heart, among other things. Taking some kind of supplement with these is a good thing. It does not however have any particular usefulness to your joints or cartilage. Chondroitin is what you want to take for joints.
Again, the poster in the background was not made by me, but rather is used by permission of Mr. Freeny of Moist Productions.