Omega Three or even Six ? necsssary if eat fish during week? Major Lack Sun Scotland

I eat eg 5 tins mackeral/sardines and cheap smoked salmon 2 days. Oa is it really benificial to take Omega 3 supplement also. I take Vitamin and D combined. Scotland being my home there is a major Vitamin D deficiency due lack of sunlight a very serious issue of all getting arthritis.Thanks