To improve your suggestion, it's very easy to also get triglyceride non-fish omega-3 (DHA+EPA), so now there shouldn't be less worry about other stuff getting into it.
As far as Omega-3 DHA and EPA, they are. It's just that you also get the algae flavor in concentrated form, and the demand is not high enough for the cost as low as fish-based supplements.
I had looked into it after seeing the modern fishing practices, and even took algae-based DHA supplements for a while. The ones I got did not contain enough EPA though, and that also has an interesting affect on mood. (Maybe I should have taken more ALA from plant sources with curcumin).
