Cod liver oil generally has a lot of Vitamin D. Generic “fish oil” is usually quite processed and doesn’t contain much nutrients outside of the Omega 3s.
Vitamin D is good and is a common thing to supplement (especially for people who don’t go out much/live in darker areas), but it can be over-consumed. Omega 3s without the Vitamin D is essentially just fat wrapped in gelatin, it can’t really be over-consumed other than just taking in too many calories (which would be hard to do with fish oil supplements).