It really comes down more to the animal's diet. Most of the mammals you and I eat are fed grains to the near-exclusion of grasses. Cattle that eat grass have the same mix of omega-3 and omega-6 fatty acids as your typical oceanic fish. The difference that gives us the "fish oils are healthy" idea is that the fish are eating their proper diet, the cattle aren't. Farm-raised fish (fed grain, just like farm-raised cattle) don't have omega 3's in anywhere near the abundance as fish that have grown up eating green plants.
That's very interesting and helpful, thank you very much!
It makes sense.